--- a/v3p/png/pngrtran.c
+++ b/v3p/png/pngrtran.c
@@ -1,11 +1,14 @@
 
 /* pngrtran.c - transforms the data in a row for PNG readers
  *
- * libpng version  1.2.8rc5 - November 29, 2004
- * For conditions of distribution and use, see copyright notice in png.h
- * Copyright (c) 1998-2004 Glenn Randers-Pehrson
+ * Last changed in libpng 1.5.10 [March 8, 2012]
+ * Copyright (c) 1998-2012 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
  *
  * This file contains functions optionally called by an application
  * in order to tell libpng how to handle data when reading a PNG.
@@ -13,55 +16,71 @@
  * in pngtrans.c.
  */
 
-#define PNG_INTERNAL
-#include "png.h"
+#include "pngpriv.h"
+
+#ifdef PNG_READ_SUPPORTED
 
 /* Set the action on getting a CRC error for an ancillary or critical chunk. */
 void PNGAPI
 png_set_crc_action(png_structp png_ptr, int crit_action, int ancil_action)
 {
-   png_debug(1, "in png_set_crc_action\n");
+   png_debug(1, "in png_set_crc_action");
+
+   if (png_ptr == NULL)
+      return;
+
    /* Tell libpng how we react to CRC errors in critical chunks */
    switch (crit_action)
    {
-      case PNG_CRC_NO_CHANGE:                        /* leave setting as is */
+      case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
          break;
-      case PNG_CRC_WARN_USE:                               /* warn/use data */
+
+      case PNG_CRC_WARN_USE:                               /* Warn/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
          break;
-      case PNG_CRC_QUIET_USE:                             /* quiet/use data */
+
+      case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                            PNG_FLAG_CRC_CRITICAL_IGNORE;
          break;
-      case PNG_CRC_WARN_DISCARD:    /* not a valid action for critical data */
-         png_warning(png_ptr, "Can't discard critical data on CRC error.");
-      case PNG_CRC_ERROR_QUIT:                                /* error/quit */
+
+      case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
+         png_warning(png_ptr,
+            "Can't discard critical data on CRC error");
+      case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
+
       case PNG_CRC_DEFAULT:
       default:
          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
          break;
    }
 
+   /* Tell libpng how we react to CRC errors in ancillary chunks */
    switch (ancil_action)
    {
-      case PNG_CRC_NO_CHANGE:                       /* leave setting as is */
+      case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
          break;
-      case PNG_CRC_WARN_USE:                              /* warn/use data */
+
+      case PNG_CRC_WARN_USE:                              /* Warn/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
          break;
-      case PNG_CRC_QUIET_USE:                            /* quiet/use data */
+
+      case PNG_CRC_QUIET_USE:                            /* Quiet/use data */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                            PNG_FLAG_CRC_ANCILLARY_NOWARN;
          break;
-      case PNG_CRC_ERROR_QUIT:                               /* error/quit */
+
+      case PNG_CRC_ERROR_QUIT:                               /* Error/quit */
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
          break;
-      case PNG_CRC_WARN_DISCARD:                      /* warn/discard data */
+
+      case PNG_CRC_WARN_DISCARD:                      /* Warn/discard data */
+
       case PNG_CRC_DEFAULT:
       default:
          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
@@ -69,67 +88,283 @@
    }
 }
 
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
-    defined(PNG_FLOATING_POINT_SUPPORTED)
-/* handle alpha and tRNS via a background color */
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
+/* Handle alpha and tRNS via a background color */
+void PNGFAPI
+png_set_background_fixed(png_structp png_ptr,
+    png_const_color_16p background_color, int background_gamma_code,
+    int need_expand, png_fixed_point background_gamma)
+{
+   png_debug(1, "in png_set_background_fixed");
+
+   if (png_ptr == NULL)
+      return;
+
+   if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
+   {
+      png_warning(png_ptr, "Application must supply a known background gamma");
+      return;
+   }
+
+   png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
+   png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+   png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+
+   png_memcpy(&(png_ptr->background), background_color,
+      png_sizeof(png_color_16));
+   png_ptr->background_gamma = background_gamma;
+   png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
+   if (need_expand)
+      png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
+   else
+      png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
+}
+
+#  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
 png_set_background(png_structp png_ptr,
-                   png_color_16p background_color, int background_gamma_code,
-                   int need_expand, double background_gamma)
+    png_const_color_16p background_color, int background_gamma_code,
+    int need_expand, double background_gamma)
 {
-   png_debug(1, "in png_set_background\n");
-   if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
-   {
-      png_warning(png_ptr, "Application must supply a known background gamma");
+   png_set_background_fixed(png_ptr, background_color, background_gamma_code,
+      need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
+}
+#  endif  /* FLOATING_POINT */
+#endif /* READ_BACKGROUND */
+
+/* Scale 16-bit depth files to 8-bit depth.  If both of these are set then the
+ * one that pngrtran does first (scale) happens.  This is necessary to allow the
+ * TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
+ */
+#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+void PNGAPI
+png_set_scale_16(png_structp png_ptr)
+{
+   png_debug(1, "in png_set_scale_16");
+
+   if (png_ptr == NULL)
       return;
-   }
-
-   png_ptr->transformations |= PNG_BACKGROUND;
-   png_memcpy(&(png_ptr->background), background_color,
-      png_sizeof(png_color_16));
-   png_ptr->background_gamma = (float)background_gamma;
-   png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
-   png_ptr->transformations |= (need_expand ? PNG_BACKGROUND_EXPAND : 0);
-
-   /* Note:  if need_expand is set and color_type is either RGB or RGB_ALPHA
-    * (in which case need_expand is superfluous anyway), the background color
-    * might actually be gray yet not be flagged as such. This is not a problem
-    * for the current code, which uses PNG_BACKGROUND_IS_GRAY only to
-    * decide when to do the png_do_gray_to_rgb() transformation.
-    */
-   if ((need_expand && !(png_ptr->color_type & PNG_COLOR_MASK_COLOR)) ||
-       (!need_expand && background_color->red == background_color->green &&
-        background_color->red == background_color->blue))
-      png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+
+   png_ptr->transformations |= PNG_SCALE_16_TO_8;
 }
 #endif
 
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
-/* strip 16 bit depth files to 8 bit depth */
+#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+/* Chop 16-bit depth files to 8-bit depth */
 void PNGAPI
 png_set_strip_16(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_strip_16\n");
+   png_debug(1, "in png_set_strip_16");
+
+   if (png_ptr == NULL)
+      return;
+
    png_ptr->transformations |= PNG_16_TO_8;
 }
 #endif
 
-#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
 void PNGAPI
 png_set_strip_alpha(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_strip_alpha\n");
-   png_ptr->flags |= PNG_FLAG_STRIP_ALPHA;
+   png_debug(1, "in png_set_strip_alpha");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->transformations |= PNG_STRIP_ALPHA;
 }
 #endif
 
-#if defined(PNG_READ_DITHER_SUPPORTED)
-/* Dither file to 8 bit.  Supply a palette, the current number
+#if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
+static png_fixed_point
+translate_gamma_flags(png_structp png_ptr, png_fixed_point output_gamma,
+   int is_screen)
+{
+   /* Check for flag values.  The main reason for having the old Mac value as a
+    * flag is that it is pretty near impossible to work out what the correct
+    * value is from Apple documentation - a working Mac system is needed to
+    * discover the value!
+    */
+   if (output_gamma == PNG_DEFAULT_sRGB ||
+      output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
+   {
+      /* If there is no sRGB support this just sets the gamma to the standard
+       * sRGB value.  (This is a side effect of using this function!)
+       */
+#     ifdef PNG_READ_sRGB_SUPPORTED
+         png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
+#     endif
+      if (is_screen)
+         output_gamma = PNG_GAMMA_sRGB;
+      else
+         output_gamma = PNG_GAMMA_sRGB_INVERSE;
+   }
+
+   else if (output_gamma == PNG_GAMMA_MAC_18 ||
+      output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
+   {
+      if (is_screen)
+         output_gamma = PNG_GAMMA_MAC_OLD;
+      else
+         output_gamma = PNG_GAMMA_MAC_INVERSE;
+   }
+
+   return output_gamma;
+}
+
+#  ifdef PNG_FLOATING_POINT_SUPPORTED
+static png_fixed_point
+convert_gamma_value(png_structp png_ptr, double output_gamma)
+{
+   /* The following silently ignores cases where fixed point (times 100,000)
+    * gamma values are passed to the floating point API.  This is safe and it
+    * means the fixed point constants work just fine with the floating point
+    * API.  The alternative would just lead to undetected errors and spurious
+    * bug reports.  Negative values fail inside the _fixed API unless they
+    * correspond to the flag values.
+    */
+   if (output_gamma > 0 && output_gamma < 128)
+      output_gamma *= PNG_FP_1;
+
+   /* This preserves -1 and -2 exactly: */
+   output_gamma = floor(output_gamma + .5);
+
+   if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
+      png_fixed_error(png_ptr, "gamma value");
+
+   return (png_fixed_point)output_gamma;
+}
+#  endif
+#endif /* READ_ALPHA_MODE || READ_GAMMA */
+
+#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
+void PNGFAPI
+png_set_alpha_mode_fixed(png_structp png_ptr, int mode,
+   png_fixed_point output_gamma)
+{
+   int compose = 0;
+   png_fixed_point file_gamma;
+
+   png_debug(1, "in png_set_alpha_mode");
+
+   if (png_ptr == NULL)
+      return;
+
+   output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);
+
+   /* Validate the value to ensure it is in a reasonable range. The value
+    * is expected to be 1 or greater, but this range test allows for some
+    * viewing correction values.  The intent is to weed out users of this API
+    * who use the inverse of the gamma value accidentally!  Since some of these
+    * values are reasonable this may have to be changed.
+    */
+   if (output_gamma < 70000 || output_gamma > 300000)
+      png_error(png_ptr, "output gamma out of expected range");
+
+   /* The default file gamma is the inverse of the output gamma; the output
+    * gamma may be changed below so get the file value first:
+    */
+   file_gamma = png_reciprocal(output_gamma);
+
+   /* There are really 8 possibilities here, composed of any combination
+    * of:
+    *
+    *    premultiply the color channels
+    *    do not encode non-opaque pixels
+    *    encode the alpha as well as the color channels
+    *
+    * The differences disappear if the input/output ('screen') gamma is 1.0,
+    * because then the encoding is a no-op and there is only the choice of
+    * premultiplying the color channels or not.
+    *
+    * png_set_alpha_mode and png_set_background interact because both use
+    * png_compose to do the work.  Calling both is only useful when
+    * png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
+    * with a default gamma value.  Otherwise PNG_COMPOSE must not be set.
+    */
+   switch (mode)
+   {
+      case PNG_ALPHA_PNG:        /* default: png standard */
+         /* No compose, but it may be set by png_set_background! */
+         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+         break;
+
+      case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
+         compose = 1;
+         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+         /* The output is linear: */
+         output_gamma = PNG_FP_1;
+         break;
+
+      case PNG_ALPHA_OPTIMIZED:  /* associated, non-opaque pixels linear */
+         compose = 1;
+         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+         png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
+         /* output_gamma records the encoding of opaque pixels! */
+         break;
+
+      case PNG_ALPHA_BROKEN:     /* associated, non-linear, alpha encoded */
+         compose = 1;
+         png_ptr->transformations |= PNG_ENCODE_ALPHA;
+         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+         break;
+
+      default:
+         png_error(png_ptr, "invalid alpha mode");
+   }
+
+   /* Only set the default gamma if the file gamma has not been set (this has
+    * the side effect that the gamma in a second call to png_set_alpha_mode will
+    * be ignored.)
+    */
+   if (png_ptr->gamma == 0)
+      png_ptr->gamma = file_gamma;
+
+   /* But always set the output gamma: */
+   png_ptr->screen_gamma = output_gamma;
+
+   /* Finally, if pre-multiplying, set the background fields to achieve the
+    * desired result.
+    */
+   if (compose)
+   {
+      /* And obtain alpha pre-multiplication by composing on black: */
+      png_memset(&png_ptr->background, 0, sizeof png_ptr->background);
+      png_ptr->background_gamma = png_ptr->gamma; /* just in case */
+      png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
+      png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
+
+      if (png_ptr->transformations & PNG_COMPOSE)
+         png_error(png_ptr,
+            "conflicting calls to set alpha mode and background");
+
+      png_ptr->transformations |= PNG_COMPOSE;
+   }
+
+   /* New API, make sure apps call the correct initializers: */
+   png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
+}
+
+#  ifdef PNG_FLOATING_POINT_SUPPORTED
+void PNGAPI
+png_set_alpha_mode(png_structp png_ptr, int mode, double output_gamma)
+{
+   png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
+      output_gamma));
+}
+#  endif
+#endif
+
+#ifdef PNG_READ_QUANTIZE_SUPPORTED
+/* Dither file to 8-bit.  Supply a palette, the current number
  * of elements in the palette, the maximum number of elements
  * allowed, and a histogram if possible.  If the current number
  * of colors is greater then the maximum number, the palette will be
- * modified to fit in the maximum number.  "full_dither" indicates
- * whether we need a dithering cube set up for RGB images, or if we
+ * modified to fit in the maximum number.  "full_quantize" indicates
+ * whether we need a quantizing cube set up for RGB images, or if we
  * simply are reducing the number of colors in a paletted image.
  */
 
@@ -143,21 +378,25 @@
 typedef png_dsort FAR * FAR * png_dsortpp;
 
 void PNGAPI
-png_set_dither(png_structp png_ptr, png_colorp palette,
-               int num_palette, int maximum_colors, png_uint_16p histogram,
-               int full_dither)
+png_set_quantize(png_structp png_ptr, png_colorp palette,
+    int num_palette, int maximum_colors, png_const_uint_16p histogram,
+    int full_quantize)
 {
-   png_debug(1, "in png_set_dither\n");
-   png_ptr->transformations |= PNG_DITHER;
-
-   if (!full_dither)
+   png_debug(1, "in png_set_quantize");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->transformations |= PNG_QUANTIZE;
+
+   if (!full_quantize)
    {
       int i;
 
-      png_ptr->dither_index = (png_bytep)png_malloc(png_ptr,
-         (png_uint_32)(num_palette * png_sizeof (png_byte)));
+      png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
+          (png_uint_32)(num_palette * png_sizeof(png_byte)));
       for (i = 0; i < num_palette; i++)
-         png_ptr->dither_index[i] = (png_byte)i;
+         png_ptr->quantize_index[i] = (png_byte)i;
    }
 
    if (num_palette > maximum_colors)
@@ -165,61 +404,66 @@
       if (histogram != NULL)
       {
          /* This is easy enough, just throw out the least used colors.
-            Perhaps not the best solution, but good enough. */
+          * Perhaps not the best solution, but good enough.
+          */
 
          int i;
 
-         /* initialize an array to sort colors */
-         png_ptr->dither_sort = (png_bytep)png_malloc(png_ptr,
-            (png_uint_32)(num_palette * png_sizeof (png_byte)));
-
-         /* initialize the dither_sort array */
+         /* Initialize an array to sort colors */
+         png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
+             (png_uint_32)(num_palette * png_sizeof(png_byte)));
+
+         /* Initialize the quantize_sort array */
          for (i = 0; i < num_palette; i++)
-            png_ptr->dither_sort[i] = (png_byte)i;
+            png_ptr->quantize_sort[i] = (png_byte)i;
 
          /* Find the least used palette entries by starting a
-            bubble sort, and running it until we have sorted
-            out enough colors.  Note that we don't care about
-            sorting all the colors, just finding which are
-            least used. */
+          * bubble sort, and running it until we have sorted
+          * out enough colors.  Note that we don't care about
+          * sorting all the colors, just finding which are
+          * least used.
+          */
 
          for (i = num_palette - 1; i >= maximum_colors; i--)
          {
-            int done; /* to stop early if the list is pre-sorted */
+            int done; /* To stop early if the list is pre-sorted */
             int j;
 
             done = 1;
             for (j = 0; j < i; j++)
             {
-               if (histogram[png_ptr->dither_sort[j]]
-                   < histogram[png_ptr->dither_sort[j + 1]])
+               if (histogram[png_ptr->quantize_sort[j]]
+                   < histogram[png_ptr->quantize_sort[j + 1]])
                {
                   png_byte t;
 
-                  t = png_ptr->dither_sort[j];
-                  png_ptr->dither_sort[j] = png_ptr->dither_sort[j + 1];
-                  png_ptr->dither_sort[j + 1] = t;
+                  t = png_ptr->quantize_sort[j];
+                  png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
+                  png_ptr->quantize_sort[j + 1] = t;
                   done = 0;
                }
             }
+
             if (done)
                break;
          }
 
-         /* swap the palette around, and set up a table, if necessary */
-         if (full_dither)
+         /* Swap the palette around, and set up a table, if necessary */
+         if (full_quantize)
          {
             int j = num_palette;
 
-            /* put all the useful colors within the max, but don't
-               move the others */
+            /* Put all the useful colors within the max, but don't
+             * move the others.
+             */
             for (i = 0; i < maximum_colors; i++)
             {
-               if ((int)png_ptr->dither_sort[i] >= maximum_colors)
+               if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                {
                   do
                      j--;
-                  while ((int)png_ptr->dither_sort[j] >= maximum_colors);
+                  while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
+
                   palette[i] = palette[j];
                }
             }
@@ -228,37 +472,38 @@
          {
             int j = num_palette;
 
-            /* move all the used colors inside the max limit, and
-               develop a translation table */
+            /* Move all the used colors inside the max limit, and
+             * develop a translation table.
+             */
             for (i = 0; i < maximum_colors; i++)
             {
-               /* only move the colors we need to */
-               if ((int)png_ptr->dither_sort[i] >= maximum_colors)
+               /* Only move the colors we need to */
+               if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                {
                   png_color tmp_color;
 
                   do
                      j--;
-                  while ((int)png_ptr->dither_sort[j] >= maximum_colors);
+                  while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
 
                   tmp_color = palette[j];
                   palette[j] = palette[i];
                   palette[i] = tmp_color;
-                  /* indicate where the color went */
-                  png_ptr->dither_index[j] = (png_byte)i;
-                  png_ptr->dither_index[i] = (png_byte)j;
-               }
-            }
-
-            /* find closest color for those colors we are not using */
+                  /* Indicate where the color went */
+                  png_ptr->quantize_index[j] = (png_byte)i;
+                  png_ptr->quantize_index[i] = (png_byte)j;
+               }
+            }
+
+            /* Find closest color for those colors we are not using */
             for (i = 0; i < num_palette; i++)
             {
-               if ((int)png_ptr->dither_index[i] >= maximum_colors)
+               if ((int)png_ptr->quantize_index[i] >= maximum_colors)
                {
                   int min_d, k, min_k, d_index;
 
-                  /* find the closest color to one we threw out */
-                  d_index = png_ptr->dither_index[i];
+                  /* Find the closest color to one we threw out */
+                  d_index = png_ptr->quantize_index[i];
                   min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
                   for (k = 1, min_k = 0; k < maximum_colors; k++)
                   {
@@ -272,61 +517,58 @@
                         min_k = k;
                      }
                   }
-                  /* point to closest color */
-                  png_ptr->dither_index[i] = (png_byte)min_k;
-               }
-            }
-         }
-         png_free(png_ptr, png_ptr->dither_sort);
-         png_ptr->dither_sort=NULL;
+                  /* Point to closest color */
+                  png_ptr->quantize_index[i] = (png_byte)min_k;
+               }
+            }
+         }
+         png_free(png_ptr, png_ptr->quantize_sort);
+         png_ptr->quantize_sort = NULL;
       }
       else
       {
          /* This is much harder to do simply (and quickly).  Perhaps
-            we need to go through a median cut routine, but those
-            don't always behave themselves with only a few colors
-            as input.  So we will just find the closest two colors,
-            and throw out one of them (chosen somewhat randomly).
-            [We don't understand this at all, so if someone wants to
-             work on improving it, be our guest - AED, GRP]
-            */
+          * we need to go through a median cut routine, but those
+          * don't always behave themselves with only a few colors
+          * as input.  So we will just find the closest two colors,
+          * and throw out one of them (chosen somewhat randomly).
+          * [We don't understand this at all, so if someone wants to
+          *  work on improving it, be our guest - AED, GRP]
+          */
          int i;
          int max_d;
          int num_new_palette;
          png_dsortp t;
          png_dsortpp hash;
 
-         t=NULL;
-
-         /* initialize palette index arrays */
+         t = NULL;
+
+         /* Initialize palette index arrays */
          png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
-            (png_uint_32)(num_palette * png_sizeof (png_byte)));
+             (png_uint_32)(num_palette * png_sizeof(png_byte)));
          png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
-            (png_uint_32)(num_palette * png_sizeof (png_byte)));
-
-         /* initialize the sort array */
+             (png_uint_32)(num_palette * png_sizeof(png_byte)));
+
+         /* Initialize the sort array */
          for (i = 0; i < num_palette; i++)
          {
             png_ptr->index_to_palette[i] = (png_byte)i;
             png_ptr->palette_to_index[i] = (png_byte)i;
          }
 
-         hash = (png_dsortpp)png_malloc(png_ptr, (png_uint_32)(769 *
-            png_sizeof (png_dsortp)));
-         for (i = 0; i < 769; i++)
-            hash[i] = NULL;
-/*         png_memset(hash, 0, 769 * png_sizeof (png_dsortp)); */
+         hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
+             png_sizeof(png_dsortp)));
 
          num_new_palette = num_palette;
 
-         /* initial wild guess at how far apart the farthest pixel
-            pair we will be eliminating will be.  Larger
-            numbers mean more areas will be allocated, Smaller
-            numbers run the risk of not saving enough data, and
-            having to do this all over again.
-
-            I have not done extensive checking on this number.
-            */
+         /* Initial wild guess at how far apart the farthest pixel
+          * pair we will be eliminating will be.  Larger
+          * numbers mean more areas will be allocated, Smaller
+          * numbers run the risk of not saving enough data, and
+          * having to do this all over again.
+          *
+          * I have not done extensive checking on this number.
+          */
          max_d = 96;
 
          while (num_new_palette > maximum_colors)
@@ -343,10 +585,13 @@
 
                   if (d <= max_d)
                   {
+
                      t = (png_dsortp)png_malloc_warn(png_ptr,
                          (png_uint_32)(png_sizeof(png_dsort)));
+
                      if (t == NULL)
                          break;
+
                      t->next = hash[d];
                      t->left = (png_byte)i;
                      t->right = (png_byte)j;
@@ -386,31 +631,36 @@
 
                         num_new_palette--;
                         palette[png_ptr->index_to_palette[j]]
-                          = palette[num_new_palette];
-                        if (!full_dither)
+                            = palette[num_new_palette];
+                        if (!full_quantize)
                         {
                            int k;
 
                            for (k = 0; k < num_palette; k++)
                            {
-                              if (png_ptr->dither_index[k] ==
+                              if (png_ptr->quantize_index[k] ==
                                   png_ptr->index_to_palette[j])
-                                 png_ptr->dither_index[k] =
-                                    png_ptr->index_to_palette[next_j];
-                              if ((int)png_ptr->dither_index[k] ==
+                                 png_ptr->quantize_index[k] =
+                                     png_ptr->index_to_palette[next_j];
+
+                              if ((int)png_ptr->quantize_index[k] ==
                                   num_new_palette)
-                                 png_ptr->dither_index[k] =
-                                    png_ptr->index_to_palette[j];
+                                 png_ptr->quantize_index[k] =
+                                     png_ptr->index_to_palette[j];
                            }
                         }
 
                         png_ptr->index_to_palette[png_ptr->palette_to_index
-                           [num_new_palette]] = png_ptr->index_to_palette[j];
+                            [num_new_palette]] = png_ptr->index_to_palette[j];
+
                         png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
-                           = png_ptr->palette_to_index[num_new_palette];
-
-                        png_ptr->index_to_palette[j] = (png_byte)num_new_palette;
-                        png_ptr->palette_to_index[num_new_palette] = (png_byte)j;
+                            = png_ptr->palette_to_index[num_new_palette];
+
+                        png_ptr->index_to_palette[j] =
+                            (png_byte)num_new_palette;
+
+                        png_ptr->palette_to_index[num_new_palette] =
+                            (png_byte)j;
                      }
                      if (num_new_palette <= maximum_colors)
                         break;
@@ -439,8 +689,8 @@
          png_free(png_ptr, hash);
          png_free(png_ptr, png_ptr->palette_to_index);
          png_free(png_ptr, png_ptr->index_to_palette);
-         png_ptr->palette_to_index=NULL;
-         png_ptr->index_to_palette=NULL;
+         png_ptr->palette_to_index = NULL;
+         png_ptr->index_to_palette = NULL;
       }
       num_palette = maximum_colors;
    }
@@ -450,40 +700,38 @@
    }
    png_ptr->num_palette = (png_uint_16)num_palette;
 
-   if (full_dither)
+   if (full_quantize)
    {
       int i;
       png_bytep distance;
-      int total_bits = PNG_DITHER_RED_BITS + PNG_DITHER_GREEN_BITS +
-         PNG_DITHER_BLUE_BITS;
-      int num_red = (1 << PNG_DITHER_RED_BITS);
-      int num_green = (1 << PNG_DITHER_GREEN_BITS);
-      int num_blue = (1 << PNG_DITHER_BLUE_BITS);
+      int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
+          PNG_QUANTIZE_BLUE_BITS;
+      int num_red = (1 << PNG_QUANTIZE_RED_BITS);
+      int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
+      int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
       png_size_t num_entries = ((png_size_t)1 << total_bits);
 
-      png_ptr->palette_lookup = (png_bytep )png_malloc(png_ptr,
-         (png_uint_32)(num_entries * png_sizeof (png_byte)));
-
-      png_memset(png_ptr->palette_lookup, 0, num_entries *
-         png_sizeof (png_byte));
+      png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
+          (png_uint_32)(num_entries * png_sizeof(png_byte)));
 
       distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
-         png_sizeof(png_byte)));
+          png_sizeof(png_byte)));
 
       png_memset(distance, 0xff, num_entries * png_sizeof(png_byte));
 
       for (i = 0; i < num_palette; i++)
       {
          int ir, ig, ib;
-         int r = (palette[i].red >> (8 - PNG_DITHER_RED_BITS));
-         int g = (palette[i].green >> (8 - PNG_DITHER_GREEN_BITS));
-         int b = (palette[i].blue >> (8 - PNG_DITHER_BLUE_BITS));
+         int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
+         int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
+         int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));
 
          for (ir = 0; ir < num_red; ir++)
          {
             /* int dr = abs(ir - r); */
             int dr = ((ir > r) ? ir - r : r - ir);
-            int index_r = (ir << (PNG_DITHER_BLUE_BITS + PNG_DITHER_GREEN_BITS));
+            int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
+                PNG_QUANTIZE_GREEN_BITS));
 
             for (ig = 0; ig < num_green; ig++)
             {
@@ -491,7 +739,7 @@
                int dg = ((ig > g) ? ig - g : g - ig);
                int dt = dr + dg;
                int dm = ((dr > dg) ? dr : dg);
-               int index_g = index_r | (ig << PNG_DITHER_BLUE_BITS);
+               int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);
 
                for (ib = 0; ib < num_blue; ib++)
                {
@@ -514,32 +762,59 @@
       png_free(png_ptr, distance);
    }
 }
-#endif
-
-#if defined(PNG_READ_GAMMA_SUPPORTED) && defined(PNG_FLOATING_POINT_SUPPORTED)
-/* Transform the image from the file_gamma to the screen_gamma.  We
- * only do transformations on images where the file_gamma and screen_gamma
- * are not close reciprocals, otherwise it slows things down slightly, and
- * also needlessly introduces small errors.
- *
- * We will turn off gamma transformation later if no semitransparent entries
- * are present in the tRNS array for palette images.  We can't do it here
- * because we don't necessarily have the tRNS chunk yet.
- */
+#endif /* PNG_READ_QUANTIZE_SUPPORTED */
+
+#ifdef PNG_READ_GAMMA_SUPPORTED
+void PNGFAPI
+png_set_gamma_fixed(png_structp png_ptr, png_fixed_point scrn_gamma,
+   png_fixed_point file_gamma)
+{
+   png_debug(1, "in png_set_gamma_fixed");
+
+   if (png_ptr == NULL)
+      return;
+
+   /* New in libpng-1.5.4 - reserve particular negative values as flags. */
+   scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
+   file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);
+
+#if PNG_LIBPNG_VER >= 10600
+   /* Checking the gamma values for being >0 was added in 1.5.4 along with the
+    * premultiplied alpha support; this actually hides an undocumented feature
+    * of the previous implementation which allowed gamma processing to be
+    * disabled in background handling.  There is no evidence (so far) that this
+    * was being used; however, png_set_background itself accepted and must still
+    * accept '0' for the gamma value it takes, because it isn't always used.
+    *
+    * Since this is an API change (albeit a very minor one that removes an
+    * undocumented API feature) it will not be made until libpng-1.6.0.
+    */
+   if (file_gamma <= 0)
+      png_error(png_ptr, "invalid file gamma in png_set_gamma");
+
+   if (scrn_gamma <= 0)
+      png_error(png_ptr, "invalid screen gamma in png_set_gamma");
+#endif
+
+   /* Set the gamma values unconditionally - this overrides the value in the PNG
+    * file if a gAMA chunk was present.  png_set_alpha_mode provides a
+    * different, easier, way to default the file gamma.
+    */
+   png_ptr->gamma = file_gamma;
+   png_ptr->screen_gamma = scrn_gamma;
+}
+
+#  ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
 png_set_gamma(png_structp png_ptr, double scrn_gamma, double file_gamma)
 {
-   png_debug(1, "in png_set_gamma\n");
-   if ((fabs(scrn_gamma * file_gamma - 1.0) > PNG_GAMMA_THRESHOLD) ||
-       (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) ||
-       (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
-     png_ptr->transformations |= PNG_GAMMA;
-   png_ptr->gamma = (float)file_gamma;
-   png_ptr->screen_gamma = (float)scrn_gamma;
+   png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
+      convert_gamma_value(png_ptr, file_gamma));
 }
-#endif
-
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#  endif /* FLOATING_POINT_SUPPORTED */
+#endif /* READ_GAMMA */
+
+#ifdef PNG_READ_EXPAND_SUPPORTED
 /* Expand paletted images to RGB, expand grayscale images of
  * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
  * to alpha channels.
@@ -547,8 +822,13 @@
 void PNGAPI
 png_set_expand(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_expand\n");
-   png_ptr->transformations |= PNG_EXPAND;
+   png_debug(1, "in png_set_expand");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 
 /* GRR 19990627:  the following three functions currently are identical
@@ -563,237 +843,719 @@
  *
  *  More to the point, these functions make it obvious what libpng will be
  *  doing, whereas "expand" can (and does) mean any number of things.
+ *
+ *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
+ *  to expand only the sample depth but not to expand the tRNS to alpha
+ *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
  */
 
 /* Expand paletted images to RGB. */
 void PNGAPI
 png_set_palette_to_rgb(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_expand\n");
-   png_ptr->transformations |= PNG_EXPAND;
+   png_debug(1, "in png_set_palette_to_rgb");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 
 /* Expand grayscale images of less than 8-bit depth to 8 bits. */
 void PNGAPI
-png_set_gray_1_2_4_to_8(png_structp png_ptr)
+png_set_expand_gray_1_2_4_to_8(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_expand\n");
+   png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
+
+   if (png_ptr == NULL)
+      return;
+
    png_ptr->transformations |= PNG_EXPAND;
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
+
+
 
 /* Expand tRNS chunks to alpha channels. */
 void PNGAPI
 png_set_tRNS_to_alpha(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_expand\n");
-   png_ptr->transformations |= PNG_EXPAND;
+   png_debug(1, "in png_set_tRNS_to_alpha");
+
+   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
 }
 #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+/* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
+ * it may not work correctly.)
+ */
+void PNGAPI
+png_set_expand_16(png_structp png_ptr)
+{
+   png_debug(1, "in png_set_expand_16");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
+
+   /* New API, make sure apps call the correct initializers: */
+   png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
+}
+#endif
+
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 void PNGAPI
 png_set_gray_to_rgb(png_structp png_ptr)
 {
-   png_debug(1, "in png_set_gray_to_rgb\n");
-   png_ptr->transformations |= PNG_GRAY_TO_RGB;
+   png_debug(1, "in png_set_gray_to_rgb");
+
+   if (png_ptr != NULL)
+   {
+      /* Because rgb must be 8 bits or more: */
+      png_set_expand_gray_1_2_4_to_8(png_ptr);
+      png_ptr->transformations |= PNG_GRAY_TO_RGB;
+      png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
+   }
 }
 #endif
 
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
-#if defined(PNG_FLOATING_POINT_SUPPORTED)
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
+void PNGFAPI
+png_set_rgb_to_gray_fixed(png_structp png_ptr, int error_action,
+    png_fixed_point red, png_fixed_point green)
+{
+   png_debug(1, "in png_set_rgb_to_gray");
+
+   if (png_ptr == NULL)
+      return;
+
+   switch(error_action)
+   {
+      case PNG_ERROR_ACTION_NONE:
+         png_ptr->transformations |= PNG_RGB_TO_GRAY;
+         break;
+
+      case PNG_ERROR_ACTION_WARN:
+         png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
+         break;
+
+      case PNG_ERROR_ACTION_ERROR:
+         png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
+         break;
+
+      default:
+         png_error(png_ptr, "invalid error action to rgb_to_gray");
+         break;
+   }
+   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
+#ifdef PNG_READ_EXPAND_SUPPORTED
+      png_ptr->transformations |= PNG_EXPAND;
+#else
+   {
+      png_warning(png_ptr,
+        "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED");
+
+      png_ptr->transformations &= ~PNG_RGB_TO_GRAY;
+   }
+#endif
+   {
+      if (red >= 0 && green >= 0 && red + green <= PNG_FP_1)
+      {
+         png_uint_16 red_int, green_int;
+
+         /* NOTE: this calculation does not round, but this behavior is retained
+          * for consistency, the inaccuracy is very small.  The code here always
+          * overwrites the coefficients, regardless of whether they have been
+          * defaulted or set already.
+          */
+         red_int = (png_uint_16)(((png_uint_32)red*32768)/100000);
+         green_int = (png_uint_16)(((png_uint_32)green*32768)/100000);
+
+         png_ptr->rgb_to_gray_red_coeff   = red_int;
+         png_ptr->rgb_to_gray_green_coeff = green_int;
+         png_ptr->rgb_to_gray_coefficients_set = 1;
+      }
+
+      else
+      {
+         if (red >= 0 && green >= 0)
+            png_warning(png_ptr,
+               "ignoring out of range rgb_to_gray coefficients");
+
+         /* Use the defaults, from the cHRM chunk if set, else the historical
+          * values which are close to the sRGB/HDTV/ITU-Rec 709 values.  See
+          * png_do_rgb_to_gray for more discussion of the values.  In this case
+          * the coefficients are not marked as 'set' and are not overwritten if
+          * something has already provided a default.
+          */
+         if (png_ptr->rgb_to_gray_red_coeff == 0 &&
+            png_ptr->rgb_to_gray_green_coeff == 0)
+         {
+            png_ptr->rgb_to_gray_red_coeff   = 6968;
+            png_ptr->rgb_to_gray_green_coeff = 23434;
+            /* png_ptr->rgb_to_gray_blue_coeff  = 2366; */
+         }
+      }
+   }
+}
+
+#ifdef PNG_FLOATING_POINT_SUPPORTED
 /* Convert a RGB image to a grayscale of the same width.  This allows us,
  * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
  */
 
 void PNGAPI
 png_set_rgb_to_gray(png_structp png_ptr, int error_action, double red,
-                    double green)
+   double green)
 {
-      int red_fixed = (int)((float)red*100000.0 + 0.5);
-      int green_fixed = (int)((float)green*100000.0 + 0.5);
-      png_set_rgb_to_gray_fixed(png_ptr, error_action, red_fixed, green_fixed);
+   if (png_ptr == NULL)
+      return;
+
+   png_set_rgb_to_gray_fixed(png_ptr, error_action,
+      png_fixed(png_ptr, red, "rgb to gray red coefficient"),
+      png_fixed(png_ptr, green, "rgb to gray green coefficient"));
 }
-#endif
-
-void PNGAPI
-png_set_rgb_to_gray_fixed(png_structp png_ptr, int error_action,
-                          png_fixed_point red, png_fixed_point green)
-{
-   png_debug(1, "in png_set_rgb_to_gray\n");
-   switch (error_action)
-   {
-      case 1: png_ptr->transformations |= PNG_RGB_TO_GRAY;
-              break;
-      case 2: png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
-              break;
-      case 3: png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
-   }
-   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-#if defined(PNG_READ_EXPAND_SUPPORTED)
-      png_ptr->transformations |= PNG_EXPAND;
-#else
-   {
-      png_warning(png_ptr, "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED.");
-      png_ptr->transformations &= ~PNG_RGB_TO_GRAY;
-   }
-#endif
-   {
-      png_uint_16 red_int, green_int;
-      if (red < 0 || green < 0)
-      {
-         red_int   =  6968; /* .212671 * 32768 + .5 */
-         green_int = 23434; /* .715160 * 32768 + .5 */
-      }
-      else if (red + green < 100000L)
-      {
-        red_int = (png_uint_16)(((png_uint_32)red*32768L)/100000L);
-        green_int = (png_uint_16)(((png_uint_32)green*32768L)/100000L);
-      }
-      else
-      {
-         png_warning(png_ptr, "ignoring out of range rgb_to_gray coefficients");
-         red_int   =  6968;
-         green_int = 23434;
-      }
-      png_ptr->rgb_to_gray_red_coeff   = red_int;
-      png_ptr->rgb_to_gray_green_coeff = green_int;
-      png_ptr->rgb_to_gray_blue_coeff  = (png_uint_16)(32768-red_int-green_int);
-   }
-}
+#endif /* FLOATING POINT */
+
 #endif
 
 #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
-    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED) || \
-    defined(PNG_LEGACY_SUPPORTED)
+    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
 void PNGAPI
 png_set_read_user_transform_fn(png_structp png_ptr, png_user_transform_ptr
-                               read_user_transform_fn)
+    read_user_transform_fn)
 {
-   png_debug(1, "in png_set_read_user_transform_fn\n");
-#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
+   png_debug(1, "in png_set_read_user_transform_fn");
+
+   if (png_ptr == NULL)
+      return;
+
+#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
    png_ptr->transformations |= PNG_USER_TRANSFORM;
    png_ptr->read_user_transform_fn = read_user_transform_fn;
 #endif
-#ifdef PNG_LEGACY_SUPPORTED
-   if (read_user_transform_fn)
-     png_warning(png_ptr,
-                 "This version of libpng does not support user transforms");
-#endif
+}
+#endif
+
+#ifdef PNG_READ_TRANSFORMS_SUPPORTED
+#ifdef PNG_READ_GAMMA_SUPPORTED
+/* In the case of gamma transformations only do transformations on images where
+ * the [file] gamma and screen_gamma are not close reciprocals, otherwise it
+ * slows things down slightly, and also needlessly introduces small errors.
+ */
+static int /* PRIVATE */
+png_gamma_threshold(png_fixed_point screen_gamma, png_fixed_point file_gamma)
+{
+   /* PNG_GAMMA_THRESHOLD is the threshold for performing gamma
+    * correction as a difference of the overall transform from 1.0
+    *
+    * We want to compare the threshold with s*f - 1, if we get
+    * overflow here it is because of wacky gamma values so we
+    * turn on processing anyway.
+    */
+   png_fixed_point gtest;
+   return !png_muldiv(&gtest, screen_gamma, file_gamma, PNG_FP_1) ||
+       png_gamma_significant(gtest);
 }
 #endif
 
 /* Initialize everything needed for the read.  This includes modifying
  * the palette.
  */
+
+/*For the moment 'png_init_palette_transformations' and
+ * 'png_init_rgb_transformations' only do some flag canceling optimizations.
+ * The intent is that these two routines should have palette or rgb operations
+ * extracted from 'png_init_read_transformations'.
+ */
+static void /* PRIVATE */
+png_init_palette_transformations(png_structp png_ptr)
+{
+   /* Called to handle the (input) palette case.  In png_do_read_transformations
+    * the first step is to expand the palette if requested, so this code must
+    * take care to only make changes that are invariant with respect to the
+    * palette expansion, or only do them if there is no expansion.
+    *
+    * STRIP_ALPHA has already been handled in the caller (by setting num_trans
+    * to 0.)
+    */
+   int input_has_alpha = 0;
+   int input_has_transparency = 0;
+
+   if (png_ptr->num_trans > 0)
+   {
+      int i;
+
+      /* Ignore if all the entries are opaque (unlikely!) */
+      for (i=0; i<png_ptr->num_trans; ++i)
+         if (png_ptr->trans_alpha[i] == 255)
+            continue;
+         else if (png_ptr->trans_alpha[i] == 0)
+            input_has_transparency = 1;
+         else
+            input_has_alpha = 1;
+   }
+
+   /* If no alpha we can optimize. */
+   if (!input_has_alpha)
+   {
+      /* Any alpha means background and associative alpha processing is
+       * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
+       * and ENCODE_ALPHA are irrelevant.
+       */
+      png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+      png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+
+      if (!input_has_transparency)
+         png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
+   }
+
+#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
+   /* png_set_background handling - deals with the complexity of whether the
+    * background color is in the file format or the screen format in the case
+    * where an 'expand' will happen.
+    */
+
+   /* The following code cannot be entered in the alpha pre-multiplication case
+    * because PNG_BACKGROUND_EXPAND is cancelled below.
+    */
+   if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
+       (png_ptr->transformations & PNG_EXPAND))
+   {
+      {
+         png_ptr->background.red   =
+             png_ptr->palette[png_ptr->background.index].red;
+         png_ptr->background.green =
+             png_ptr->palette[png_ptr->background.index].green;
+         png_ptr->background.blue  =
+             png_ptr->palette[png_ptr->background.index].blue;
+
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
+        if (png_ptr->transformations & PNG_INVERT_ALPHA)
+        {
+           if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
+           {
+              /* Invert the alpha channel (in tRNS) unless the pixels are
+               * going to be expanded, in which case leave it for later
+               */
+              int i, istop = png_ptr->num_trans;
+
+              for (i=0; i<istop; i++)
+                 png_ptr->trans_alpha[i] = (png_byte)(255 -
+                    png_ptr->trans_alpha[i]);
+           }
+        }
+#endif /* PNG_READ_INVERT_ALPHA_SUPPORTED */
+      }
+   } /* background expand and (therefore) no alpha association. */
+#endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
+}
+
+static void /* PRIVATE */
+png_init_rgb_transformations(png_structp png_ptr)
+{
+   /* Added to libpng-1.5.4: check the color type to determine whether there
+    * is any alpha or transparency in the image and simply cancel the
+    * background and alpha mode stuff if there isn't.
+    */
+   int input_has_alpha = (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0;
+   int input_has_transparency = png_ptr->num_trans > 0;
+
+   /* If no alpha we can optimize. */
+   if (!input_has_alpha)
+   {
+      /* Any alpha means background and associative alpha processing is
+       * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
+       * and ENCODE_ALPHA are irrelevant.
+       */
+#     ifdef PNG_READ_ALPHA_MODE_SUPPORTED
+         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+#     endif
+
+      if (!input_has_transparency)
+         png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
+   }
+
+#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
+   /* png_set_background handling - deals with the complexity of whether the
+    * background color is in the file format or the screen format in the case
+    * where an 'expand' will happen.
+    */
+
+   /* The following code cannot be entered in the alpha pre-multiplication case
+    * because PNG_BACKGROUND_EXPAND is cancelled below.
+    */
+   if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
+       (png_ptr->transformations & PNG_EXPAND) &&
+       !(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
+       /* i.e., GRAY or GRAY_ALPHA */
+   {
+      {
+         /* Expand background and tRNS chunks */
+         int gray = png_ptr->background.gray;
+         int trans_gray = png_ptr->trans_color.gray;
+
+         switch (png_ptr->bit_depth)
+         {
+            case 1:
+               gray *= 0xff;
+               trans_gray *= 0xff;
+               break;
+
+            case 2:
+               gray *= 0x55;
+               trans_gray *= 0x55;
+               break;
+
+            case 4:
+               gray *= 0x11;
+               trans_gray *= 0x11;
+               break;
+
+            default:
+
+            case 8:
+               /* Already 8 bits, fall through */
+
+            case 16:
+               /* Already a full 16 bits */
+               break;
+         }
+
+         png_ptr->background.red = png_ptr->background.green =
+            png_ptr->background.blue = (png_uint_16)gray;
+
+         if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
+         {
+            png_ptr->trans_color.red = png_ptr->trans_color.green =
+               png_ptr->trans_color.blue = (png_uint_16)trans_gray;
+         }
+      }
+   } /* background expand and (therefore) no alpha association. */
+#endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
+}
+
 void /* PRIVATE */
 png_init_read_transformations(png_structp png_ptr)
 {
-   png_debug(1, "in png_init_read_transformations\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (png_ptr != NULL)
-#endif
-  {
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) || defined(PNG_READ_SHIFT_SUPPORTED) \
- || defined(PNG_READ_GAMMA_SUPPORTED)
-   int color_type = png_ptr->color_type;
-#endif
-
-#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
-   if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
-       (png_ptr->transformations & PNG_EXPAND))
-   {
-      if (!(color_type & PNG_COLOR_MASK_COLOR))  /* i.e., GRAY or GRAY_ALPHA */
-      {
-         /* expand background chunk. */
-         switch (png_ptr->bit_depth)
-         {
-            case 1:
-               png_ptr->background.gray *= (png_uint_16)0xff;
-               png_ptr->background.red = png_ptr->background.green
-                 =  png_ptr->background.blue = png_ptr->background.gray;
-               break;
-            case 2:
-               png_ptr->background.gray *= (png_uint_16)0x55;
-               png_ptr->background.red = png_ptr->background.green
-                 = png_ptr->background.blue = png_ptr->background.gray;
-               break;
-            case 4:
-               png_ptr->background.gray *= (png_uint_16)0x11;
-               png_ptr->background.red = png_ptr->background.green
-                 = png_ptr->background.blue = png_ptr->background.gray;
-               break;
-            case 8:
-            case 16:
-               png_ptr->background.red = png_ptr->background.green
-                 = png_ptr->background.blue = png_ptr->background.gray;
-               break;
-         }
-      }
-      else if (color_type == PNG_COLOR_TYPE_PALETTE)
-      {
-         png_ptr->background.red   =
-            png_ptr->palette[png_ptr->background.index].red;
-         png_ptr->background.green =
-            png_ptr->palette[png_ptr->background.index].green;
-         png_ptr->background.blue  =
-            png_ptr->palette[png_ptr->background.index].blue;
-
-#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
-        if (png_ptr->transformations & PNG_INVERT_ALPHA)
-        {
-#if defined(PNG_READ_EXPAND_SUPPORTED)
-           if (!(png_ptr->transformations & PNG_EXPAND))
-#endif
-           {
-           /* invert the alpha channel (in tRNS) unless the pixels are
-              going to be expanded, in which case leave it for later */
-              int i,istop;
-              istop=(int)png_ptr->num_trans;
-              for (i=0; i<istop; i++)
-                 png_ptr->trans[i] = (png_byte)(255 - png_ptr->trans[i]);
-           }
-        }
-#endif
-      }
-   }
-#endif
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) && defined(PNG_READ_GAMMA_SUPPORTED)
-   png_ptr->background_1 = png_ptr->background;
-#endif
-#if defined(PNG_READ_GAMMA_SUPPORTED) && defined(PNG_FLOATING_POINT_SUPPORTED)
-
-   if ((color_type == PNG_COLOR_TYPE_PALETTE && png_ptr->num_trans != 0)
-       && (fabs(png_ptr->screen_gamma * png_ptr->gamma - 1.0)
-         < PNG_GAMMA_THRESHOLD))
-   {
-    int i,k;
-    k=0;
-    for (i=0; i<png_ptr->num_trans; i++)
-    {
-      if (png_ptr->trans[i] != 0 && png_ptr->trans[i] != 0xff)
-        k=1; /* partial transparency is present */
-    }
-    if (k == 0)
-      png_ptr->transformations &= (~PNG_GAMMA);
-   }
-
-   if (png_ptr->transformations & (PNG_GAMMA | PNG_RGB_TO_GRAY))
-   {
-      png_build_gamma_table(png_ptr);
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-      if (png_ptr->transformations & PNG_BACKGROUND)
-      {
-         if (color_type == PNG_COLOR_TYPE_PALETTE)
-         {
-           /* could skip if no transparency and
-           */
+   png_debug(1, "in png_init_read_transformations");
+
+   /* This internal function is called from png_read_start_row in pngrutil.c
+    * and it is called before the 'rowbytes' calculation is done, so the code
+    * in here can change or update the transformations flags.
+    *
+    * First do updates that do not depend on the details of the PNG image data
+    * being processed.
+    */
+
+#ifdef PNG_READ_GAMMA_SUPPORTED
+   /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
+    * png_set_alpha_mode and this is another source for a default file gamma so
+    * the test needs to be performed later - here.  In addition prior to 1.5.4
+    * the tests were repeated for the PALETTE color type here - this is no
+    * longer necessary (and doesn't seem to have been necessary before.)
+    */
+   {
+      /* The following temporary indicates if overall gamma correction is
+       * required.
+       */
+      int gamma_correction = 0;
+
+      if (png_ptr->gamma != 0) /* has been set */
+      {
+         if (png_ptr->screen_gamma != 0) /* screen set too */
+            gamma_correction = png_gamma_threshold(png_ptr->gamma,
+               png_ptr->screen_gamma);
+
+         else
+            /* Assume the output matches the input; a long time default behavior
+             * of libpng, although the standard has nothing to say about this.
+             */
+            png_ptr->screen_gamma = png_reciprocal(png_ptr->gamma);
+      }
+
+      else if (png_ptr->screen_gamma != 0)
+         /* The converse - assume the file matches the screen, note that this
+          * perhaps undesireable default can (from 1.5.4) be changed by calling
+          * png_set_alpha_mode (even if the alpha handling mode isn't required
+          * or isn't changed from the default.)
+          */
+         png_ptr->gamma = png_reciprocal(png_ptr->screen_gamma);
+
+      else /* neither are set */
+         /* Just in case the following prevents any processing - file and screen
+          * are both assumed to be linear and there is no way to introduce a
+          * third gamma value other than png_set_background with 'UNIQUE', and,
+          * prior to 1.5.4
+          */
+         png_ptr->screen_gamma = png_ptr->gamma = PNG_FP_1;
+
+      /* Now turn the gamma transformation on or off as appropriate.  Notice
+       * that PNG_GAMMA just refers to the file->screen correction.  Alpha
+       * composition may independently cause gamma correction because it needs
+       * linear data (e.g. if the file has a gAMA chunk but the screen gamma
+       * hasn't been specified.)  In any case this flag may get turned off in
+       * the code immediately below if the transform can be handled outside the
+       * row loop.
+       */
+      if (gamma_correction)
+         png_ptr->transformations |= PNG_GAMMA;
+
+      else
+         png_ptr->transformations &= ~PNG_GAMMA;
+   }
+#endif
+
+   /* Certain transformations have the effect of preventing other
+    * transformations that happen afterward in png_do_read_transformations,
+    * resolve the interdependencies here.  From the code of
+    * png_do_read_transformations the order is:
+    *
+    *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
+    *  2) PNG_STRIP_ALPHA (if no compose)
+    *  3) PNG_RGB_TO_GRAY
+    *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
+    *  5) PNG_COMPOSE
+    *  6) PNG_GAMMA
+    *  7) PNG_STRIP_ALPHA (if compose)
+    *  8) PNG_ENCODE_ALPHA
+    *  9) PNG_SCALE_16_TO_8
+    * 10) PNG_16_TO_8
+    * 11) PNG_QUANTIZE (converts to palette)
+    * 12) PNG_EXPAND_16
+    * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
+    * 14) PNG_INVERT_MONO
+    * 15) PNG_SHIFT
+    * 16) PNG_PACK
+    * 17) PNG_BGR
+    * 18) PNG_PACKSWAP
+    * 19) PNG_FILLER (includes PNG_ADD_ALPHA)
+    * 20) PNG_INVERT_ALPHA
+    * 21) PNG_SWAP_ALPHA
+    * 22) PNG_SWAP_BYTES
+    * 23) PNG_USER_TRANSFORM [must be last]
+    */
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
+   if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
+      !(png_ptr->transformations & PNG_COMPOSE))
+   {
+      /* Stripping the alpha channel happens immediately after the 'expand'
+       * transformations, before all other transformation, so it cancels out
+       * the alpha handling.  It has the side effect negating the effect of
+       * PNG_EXPAND_tRNS too:
+       */
+      png_ptr->transformations &= ~(PNG_BACKGROUND_EXPAND | PNG_ENCODE_ALPHA |
+         PNG_EXPAND_tRNS);
+      png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+
+      /* Kill the tRNS chunk itself too.  Prior to 1.5.4 this did not happen
+       * so transparency information would remain just so long as it wasn't
+       * expanded.  This produces unexpected API changes if the set of things
+       * that do PNG_EXPAND_tRNS changes (perfectly possible given the
+       * documentation - which says ask for what you want, accept what you
+       * get.)  This makes the behavior consistent from 1.5.4:
+       */
+      png_ptr->num_trans = 0;
+   }
+#endif /* STRIP_ALPHA supported, no COMPOSE */
+
+#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
+   /* If the screen gamma is about 1.0 then the OPTIMIZE_ALPHA and ENCODE_ALPHA
+    * settings will have no effect.
+    */
+   if (!png_gamma_significant(png_ptr->screen_gamma))
+   {
+      png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
+      png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
+   }
+#endif
+
+#if defined(PNG_READ_EXPAND_SUPPORTED) && \
+   defined(PNG_READ_BACKGROUND_SUPPORTED) && \
+   defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+   /* Detect gray background and attempt to enable optimization for
+    * gray --> RGB case.
+    *
+    * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
+    * RGB_ALPHA (in which case need_expand is superfluous anyway), the
+    * background color might actually be gray yet not be flagged as such.
+    * This is not a problem for the current code, which uses
+    * PNG_BACKGROUND_IS_GRAY only to decide when to do the
+    * png_do_gray_to_rgb() transformation.
+    *
+    * TODO: this code needs to be revised to avoid the complexity and
+    * interdependencies.  The color type of the background should be recorded in
+    * png_set_background, along with the bit depth, then the code has a record
+    * of exactly what color space the background is currently in.
+    */
+   if (png_ptr->transformations & PNG_BACKGROUND_EXPAND)
+   {
+      /* PNG_BACKGROUND_EXPAND: the background is in the file color space, so if
+       * the file was grayscale the background value is gray.
+       */
+      if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
+         png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+   }
+
+   else if (png_ptr->transformations & PNG_COMPOSE)
+   {
+      /* PNG_COMPOSE: png_set_background was called with need_expand false,
+       * so the color is in the color space of the output or png_set_alpha_mode
+       * was called and the color is black.  Ignore RGB_TO_GRAY because that
+       * happens before GRAY_TO_RGB.
+       */
+      if (png_ptr->transformations & PNG_GRAY_TO_RGB)
+      {
+         if (png_ptr->background.red == png_ptr->background.green &&
+             png_ptr->background.red == png_ptr->background.blue)
+         {
+            png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+            png_ptr->background.gray = png_ptr->background.red;
+         }
+      }
+   }
+#endif /* PNG_READ_GRAY_TO_RGB_SUPPORTED (etc) */
+
+   /* For indexed PNG data (PNG_COLOR_TYPE_PALETTE) many of the transformations
+    * can be performed directly on the palette, and some (such as rgb to gray)
+    * can be optimized inside the palette.  This is particularly true of the
+    * composite (background and alpha) stuff, which can be pretty much all done
+    * in the palette even if the result is expanded to RGB or gray afterward.
+    *
+    * NOTE: this is Not Yet Implemented, the code behaves as in 1.5.1 and
+    * earlier and the palette stuff is actually handled on the first row.  This
+    * leads to the reported bug that the palette returned by png_get_PLTE is not
+    * updated.
+    */
+   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
+      png_init_palette_transformations(png_ptr);
+
+   else
+      png_init_rgb_transformations(png_ptr);
+
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
+   defined(PNG_READ_EXPAND_16_SUPPORTED)
+   if ((png_ptr->transformations & PNG_EXPAND_16) &&
+      (png_ptr->transformations & PNG_COMPOSE) &&
+      !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
+      png_ptr->bit_depth != 16)
+   {
+      /* TODO: fix this.  Because the expand_16 operation is after the compose
+       * handling the background color must be 8, not 16, bits deep, but the
+       * application will supply a 16-bit value so reduce it here.
+       *
+       * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
+       * present, so that case is ok (until do_expand_16 is moved.)
+       *
+       * NOTE: this discards the low 16 bits of the user supplied background
+       * color, but until expand_16 works properly there is no choice!
+       */
+#     define CHOP(x) (x)=((png_uint_16)(((png_uint_32)(x)*255+32895) >> 16))
+      CHOP(png_ptr->background.red);
+      CHOP(png_ptr->background.green);
+      CHOP(png_ptr->background.blue);
+      CHOP(png_ptr->background.gray);
+#     undef CHOP
+   }
+#endif /* PNG_READ_BACKGROUND_SUPPORTED && PNG_READ_EXPAND_16_SUPPORTED */
+
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
+   (defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
+   defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
+   if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) &&
+      (png_ptr->transformations & PNG_COMPOSE) &&
+      !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
+      png_ptr->bit_depth == 16)
+   {
+      /* On the other hand, if a 16-bit file is to be reduced to 8-bits per
+       * component this will also happen after PNG_COMPOSE and so the background
+       * color must be pre-expanded here.
+       *
+       * TODO: fix this too.
+       */
+      png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
+      png_ptr->background.green =
+         (png_uint_16)(png_ptr->background.green * 257);
+      png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
+      png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
+   }
+#endif
+
+   /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
+    * background support (see the comments in scripts/pnglibconf.dfa), this
+    * allows pre-multiplication of the alpha channel to be implemented as
+    * compositing on black.  This is probably sub-optimal and has been done in
+    * 1.5.4 betas simply to enable external critique and testing (i.e. to
+    * implement the new API quickly, without lots of internal changes.)
+    */
+
+#ifdef PNG_READ_GAMMA_SUPPORTED
+#  ifdef PNG_READ_BACKGROUND_SUPPORTED
+      /* Includes ALPHA_MODE */
+      png_ptr->background_1 = png_ptr->background;
+#  endif
+
+   /* This needs to change - in the palette image case a whole set of tables are
+    * built when it would be quicker to just calculate the correct value for
+    * each palette entry directly.  Also, the test is too tricky - why check
+    * PNG_RGB_TO_GRAY if PNG_GAMMA is not set?  The answer seems to be that
+    * PNG_GAMMA is cancelled even if the gamma is known?  The test excludes the
+    * PNG_COMPOSE case, so apparently if there is no *overall* gamma correction
+    * the gamma tables will not be built even if composition is required on a
+    * gamma encoded value.
+    *
+    * In 1.5.4 this is addressed below by an additional check on the individual
+    * file gamma - if it is not 1.0 both RGB_TO_GRAY and COMPOSE need the
+    * tables.
+    */
+   if ((png_ptr->transformations & PNG_GAMMA)
+      || ((png_ptr->transformations & PNG_RGB_TO_GRAY)
+         && (png_gamma_significant(png_ptr->gamma) ||
+            png_gamma_significant(png_ptr->screen_gamma)))
+      || ((png_ptr->transformations & PNG_COMPOSE)
+         && (png_gamma_significant(png_ptr->gamma)
+            || png_gamma_significant(png_ptr->screen_gamma)
+#  ifdef PNG_READ_BACKGROUND_SUPPORTED
+            || (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_UNIQUE
+               && png_gamma_significant(png_ptr->background_gamma))
+#  endif
+      )) || ((png_ptr->transformations & PNG_ENCODE_ALPHA)
+         && png_gamma_significant(png_ptr->screen_gamma))
+      )
+   {
+      png_build_gamma_table(png_ptr, png_ptr->bit_depth);
+
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
+      if (png_ptr->transformations & PNG_COMPOSE)
+      {
+         /* Issue a warning about this combination: because RGB_TO_GRAY is
+          * optimized to do the gamma transform if present yet do_background has
+          * to do the same thing if both options are set a
+          * double-gamma-correction happens.  This is true in all versions of
+          * libpng to date.
+          */
+         if (png_ptr->transformations & PNG_RGB_TO_GRAY)
+            png_warning(png_ptr,
+               "libpng does not support gamma+background+rgb_to_gray");
+
+         if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
+         {
+            /* We don't get to here unless there is a tRNS chunk with non-opaque
+             * entries - see the checking code at the start of this function.
+             */
             png_color back, back_1;
             png_colorp palette = png_ptr->palette;
             int num_palette = png_ptr->num_palette;
             int i;
             if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
             {
+
                back.red = png_ptr->gamma_table[png_ptr->background.red];
                back.green = png_ptr->gamma_table[png_ptr->background.green];
                back.blue = png_ptr->gamma_table[png_ptr->background.blue];
@@ -804,73 +1566,90 @@
             }
             else
             {
-               double g, gs;
+               png_fixed_point g, gs;
 
                switch (png_ptr->background_gamma_type)
                {
                   case PNG_BACKGROUND_GAMMA_SCREEN:
                      g = (png_ptr->screen_gamma);
-                     gs = 1.0;
+                     gs = PNG_FP_1;
                      break;
+
                   case PNG_BACKGROUND_GAMMA_FILE:
-                     g = 1.0 / (png_ptr->gamma);
-                     gs = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
+                     g = png_reciprocal(png_ptr->gamma);
+                     gs = png_reciprocal2(png_ptr->gamma,
+                        png_ptr->screen_gamma);
                      break;
+
                   case PNG_BACKGROUND_GAMMA_UNIQUE:
-                     g = 1.0 / (png_ptr->background_gamma);
-                     gs = 1.0 / (png_ptr->background_gamma *
-                                 png_ptr->screen_gamma);
+                     g = png_reciprocal(png_ptr->background_gamma);
+                     gs = png_reciprocal2(png_ptr->background_gamma,
+                        png_ptr->screen_gamma);
                      break;
                   default:
-                     g = 1.0;    /* back_1 */
-                     gs = 1.0;   /* back */
-               }
-
-               if ( fabs(gs - 1.0) < PNG_GAMMA_THRESHOLD)
+                     g = PNG_FP_1;    /* back_1 */
+                     gs = PNG_FP_1;   /* back */
+                     break;
+               }
+
+               if (png_gamma_significant(gs))
+               {
+                  back.red = png_gamma_8bit_correct(png_ptr->background.red,
+                      gs);
+                  back.green = png_gamma_8bit_correct(png_ptr->background.green,
+                      gs);
+                  back.blue = png_gamma_8bit_correct(png_ptr->background.blue,
+                      gs);
+               }
+
+               else
                {
                   back.red   = (png_byte)png_ptr->background.red;
                   back.green = (png_byte)png_ptr->background.green;
                   back.blue  = (png_byte)png_ptr->background.blue;
                }
+
+               if (png_gamma_significant(g))
+               {
+                  back_1.red = png_gamma_8bit_correct(png_ptr->background.red,
+                     g);
+                  back_1.green = png_gamma_8bit_correct(
+                     png_ptr->background.green, g);
+                  back_1.blue = png_gamma_8bit_correct(png_ptr->background.blue,
+                     g);
+               }
+
                else
                {
-                  back.red = (png_byte)(pow(
-                     (double)png_ptr->background.red/255, gs) * 255.0 + .5);
-                  back.green = (png_byte)(pow(
-                     (double)png_ptr->background.green/255, gs) * 255.0 + .5);
-                  back.blue = (png_byte)(pow(
-                     (double)png_ptr->background.blue/255, gs) * 255.0 + .5);
-               }
-
-               back_1.red = (png_byte)(pow(
-                  (double)png_ptr->background.red/255, g) * 255.0 + .5);
-               back_1.green = (png_byte)(pow(
-                  (double)png_ptr->background.green/255, g) * 255.0 + .5);
-               back_1.blue = (png_byte)(pow(
-                  (double)png_ptr->background.blue/255, g) * 255.0 + .5);
-            }
+                  back_1.red   = (png_byte)png_ptr->background.red;
+                  back_1.green = (png_byte)png_ptr->background.green;
+                  back_1.blue  = (png_byte)png_ptr->background.blue;
+               }
+            }
+
             for (i = 0; i < num_palette; i++)
             {
-               if (i < (int)png_ptr->num_trans && png_ptr->trans[i] != 0xff)
-               {
-                  if (png_ptr->trans[i] == 0)
+               if (i < (int)png_ptr->num_trans &&
+                   png_ptr->trans_alpha[i] != 0xff)
+               {
+                  if (png_ptr->trans_alpha[i] == 0)
                   {
                      palette[i] = back;
                   }
-                  else /* if (png_ptr->trans[i] != 0xff) */
+                  else /* if (png_ptr->trans_alpha[i] != 0xff) */
                   {
                      png_byte v, w;
 
                      v = png_ptr->gamma_to_1[palette[i].red];
-                     png_composite(w, v, png_ptr->trans[i], back_1.red);
+                     png_composite(w, v, png_ptr->trans_alpha[i], back_1.red);
                      palette[i].red = png_ptr->gamma_from_1[w];
 
                      v = png_ptr->gamma_to_1[palette[i].green];
-                     png_composite(w, v, png_ptr->trans[i], back_1.green);
+                     png_composite(w, v, png_ptr->trans_alpha[i], back_1.green);
                      palette[i].green = png_ptr->gamma_from_1[w];
 
                      v = png_ptr->gamma_to_1[palette[i].blue];
-                     png_composite(w, v, png_ptr->trans[i], back_1.blue);
+                     png_composite(w, v, png_ptr->trans_alpha[i], back_1.blue);
                      palette[i].blue = png_ptr->gamma_from_1[w];
                   }
                }
@@ -881,90 +1660,139 @@
                   palette[i].blue = png_ptr->gamma_table[palette[i].blue];
                }
             }
-         }
+
+            /* Prevent the transformations being done again.
+             *
+             * NOTE: this is highly dubious; it removes the transformations in
+             * place.  This seems inconsistent with the general treatment of the
+             * transformations elsewhere.
+             */
+            png_ptr->transformations &= ~(PNG_COMPOSE | PNG_GAMMA);
+         } /* color_type == PNG_COLOR_TYPE_PALETTE */
+
          /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
-         else
-         /* color_type != PNG_COLOR_TYPE_PALETTE */
-         {
-            double m = (double)(((png_uint_32)1 << png_ptr->bit_depth) - 1);
-            double g = 1.0;
-            double gs = 1.0;
+         else /* color_type != PNG_COLOR_TYPE_PALETTE */
+         {
+            int gs_sig, g_sig;
+            png_fixed_point g = PNG_FP_1;  /* Correction to linear */
+            png_fixed_point gs = PNG_FP_1; /* Correction to screen */
 
             switch (png_ptr->background_gamma_type)
             {
                case PNG_BACKGROUND_GAMMA_SCREEN:
-                  g = (png_ptr->screen_gamma);
-                  gs = 1.0;
+                  g = png_ptr->screen_gamma;
+                  /* gs = PNG_FP_1; */
                   break;
+
                case PNG_BACKGROUND_GAMMA_FILE:
-                  g = 1.0 / (png_ptr->gamma);
-                  gs = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
+                  g = png_reciprocal(png_ptr->gamma);
+                  gs = png_reciprocal2(png_ptr->gamma, png_ptr->screen_gamma);
                   break;
+
                case PNG_BACKGROUND_GAMMA_UNIQUE:
-                  g = 1.0 / (png_ptr->background_gamma);
-                  gs = 1.0 / (png_ptr->background_gamma *
-                     png_ptr->screen_gamma);
+                  g = png_reciprocal(png_ptr->background_gamma);
+                  gs = png_reciprocal2(png_ptr->background_gamma,
+                      png_ptr->screen_gamma);
                   break;
-            }
-
-            png_ptr->background_1.gray = (png_uint_16)(pow(
-               (double)png_ptr->background.gray / m, g) * m + .5);
-            png_ptr->background.gray = (png_uint_16)(pow(
-               (double)png_ptr->background.gray / m, gs) * m + .5);
+
+               default:
+                  png_error(png_ptr, "invalid background gamma type");
+            }
+
+            g_sig = png_gamma_significant(g);
+            gs_sig = png_gamma_significant(gs);
+
+            if (g_sig)
+               png_ptr->background_1.gray = png_gamma_correct(png_ptr,
+                   png_ptr->background.gray, g);
+
+            if (gs_sig)
+               png_ptr->background.gray = png_gamma_correct(png_ptr,
+                   png_ptr->background.gray, gs);
 
             if ((png_ptr->background.red != png_ptr->background.green) ||
                 (png_ptr->background.red != png_ptr->background.blue) ||
                 (png_ptr->background.red != png_ptr->background.gray))
             {
                /* RGB or RGBA with color background */
-               png_ptr->background_1.red = (png_uint_16)(pow(
-                  (double)png_ptr->background.red / m, g) * m + .5);
-               png_ptr->background_1.green = (png_uint_16)(pow(
-                  (double)png_ptr->background.green / m, g) * m + .5);
-               png_ptr->background_1.blue = (png_uint_16)(pow(
-                  (double)png_ptr->background.blue / m, g) * m + .5);
-               png_ptr->background.red = (png_uint_16)(pow(
-                  (double)png_ptr->background.red / m, gs) * m + .5);
-               png_ptr->background.green = (png_uint_16)(pow(
-                  (double)png_ptr->background.green / m, gs) * m + .5);
-               png_ptr->background.blue = (png_uint_16)(pow(
-                  (double)png_ptr->background.blue / m, gs) * m + .5);
-            }
+               if (g_sig)
+               {
+                  png_ptr->background_1.red = png_gamma_correct(png_ptr,
+                      png_ptr->background.red, g);
+
+                  png_ptr->background_1.green = png_gamma_correct(png_ptr,
+                      png_ptr->background.green, g);
+
+                  png_ptr->background_1.blue = png_gamma_correct(png_ptr,
+                      png_ptr->background.blue, g);
+               }
+
+               if (gs_sig)
+               {
+                  png_ptr->background.red = png_gamma_correct(png_ptr,
+                      png_ptr->background.red, gs);
+
+                  png_ptr->background.green = png_gamma_correct(png_ptr,
+                      png_ptr->background.green, gs);
+
+                  png_ptr->background.blue = png_gamma_correct(png_ptr,
+                      png_ptr->background.blue, gs);
+               }
+            }
+
             else
             {
                /* GRAY, GRAY ALPHA, RGB, or RGBA with gray background */
                png_ptr->background_1.red = png_ptr->background_1.green
-                 = png_ptr->background_1.blue = png_ptr->background_1.gray;
+                   = png_ptr->background_1.blue = png_ptr->background_1.gray;
+
                png_ptr->background.red = png_ptr->background.green
-                 = png_ptr->background.blue = png_ptr->background.gray;
-            }
-         }
-      }
+                   = png_ptr->background.blue = png_ptr->background.gray;
+            }
+
+            /* The background is now in screen gamma: */
+            png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
+         } /* color_type != PNG_COLOR_TYPE_PALETTE */
+      }/* png_ptr->transformations & PNG_BACKGROUND */
+
       else
-      /* transformation does not include PNG_BACKGROUND */
+      /* Transformation does not include PNG_BACKGROUND */
 #endif /* PNG_READ_BACKGROUND_SUPPORTED */
-      if (color_type == PNG_COLOR_TYPE_PALETTE)
+      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
+         /* RGB_TO_GRAY needs to have non-gamma-corrected values! */
+         && ((png_ptr->transformations & PNG_EXPAND) == 0 ||
+         (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
+#endif
+         )
       {
          png_colorp palette = png_ptr->palette;
          int num_palette = png_ptr->num_palette;
          int i;
 
+         /*NOTE: there are other transformations that should probably be in here
+          * too.
+          */
          for (i = 0; i < num_palette; i++)
          {
             palette[i].red = png_ptr->gamma_table[palette[i].red];
             palette[i].green = png_ptr->gamma_table[palette[i].green];
             palette[i].blue = png_ptr->gamma_table[palette[i].blue];
          }
-      }
-   }
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+
+         /* Done the gamma correction. */
+         png_ptr->transformations &= ~PNG_GAMMA;
+      } /* color_type == PALETTE && !PNG_BACKGROUND transformation */
+   }
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
    else
 #endif
-#endif /* PNG_READ_GAMMA_SUPPORTED && PNG_FLOATING_POINT_SUPPORTED */
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-   /* No GAMMA transformation */
-   if ((png_ptr->transformations & PNG_BACKGROUND) &&
-       (color_type == PNG_COLOR_TYPE_PALETTE))
+#endif /* PNG_READ_GAMMA_SUPPORTED */
+
+#ifdef PNG_READ_BACKGROUND_SUPPORTED
+   /* No GAMMA transformation (see the hanging else 4 lines above) */
+   if ((png_ptr->transformations & PNG_COMPOSE) &&
+       (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
    {
       int i;
       int istop = (int)png_ptr->num_trans;
@@ -977,54 +1805,71 @@
 
       for (i = 0; i < istop; i++)
       {
-         if (png_ptr->trans[i] == 0)
+         if (png_ptr->trans_alpha[i] == 0)
          {
             palette[i] = back;
          }
-         else if (png_ptr->trans[i] != 0xff)
+
+         else if (png_ptr->trans_alpha[i] != 0xff)
          {
             /* The png_composite() macro is defined in png.h */
             png_composite(palette[i].red, palette[i].red,
-               png_ptr->trans[i], back.red);
+                png_ptr->trans_alpha[i], back.red);
+
             png_composite(palette[i].green, palette[i].green,
-               png_ptr->trans[i], back.green);
+                png_ptr->trans_alpha[i], back.green);
+
             png_composite(palette[i].blue, palette[i].blue,
-               png_ptr->trans[i], back.blue);
-         }
-      }
+                png_ptr->trans_alpha[i], back.blue);
+         }
+      }
+
+      png_ptr->transformations &= ~PNG_COMPOSE;
    }
 #endif /* PNG_READ_BACKGROUND_SUPPORTED */
 
-#if defined(PNG_READ_SHIFT_SUPPORTED)
+#ifdef PNG_READ_SHIFT_SUPPORTED
    if ((png_ptr->transformations & PNG_SHIFT) &&
-      (color_type == PNG_COLOR_TYPE_PALETTE))
-   {
-      png_uint_16 i;
-      png_uint_16 istop = png_ptr->num_palette;
-      int sr = 8 - png_ptr->sig_bit.red;
-      int sg = 8 - png_ptr->sig_bit.green;
-      int sb = 8 - png_ptr->sig_bit.blue;
-
-      if (sr < 0 || sr > 8)
-        sr = 0;
-      if (sg < 0 || sg > 8)
-        sg = 0;
-      if (sb < 0 || sb > 8)
-        sb = 0;
-      for (i = 0; i < istop; i++)
-      {
-         png_ptr->palette[i].red >>= sr;
-         png_ptr->palette[i].green >>= sg;
-         png_ptr->palette[i].blue >>= sb;
+      !(png_ptr->transformations & PNG_EXPAND) &&
+       (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
+   {
+      int i;
+      int istop = png_ptr->num_palette;
+      int shift = 8 - png_ptr->sig_bit.red;
+
+      png_ptr->transformations &= ~PNG_SHIFT;
+
+      /* significant bits can be in the range 1 to 7 for a meaninful result, if
+       * the number of significant bits is 0 then no shift is done (this is an
+       * error condition which is silently ignored.)
+       */
+      if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
+      {
+         int component = png_ptr->palette[i].red;
+
+         component >>= shift;
+         png_ptr->palette[i].red = (png_byte)component;
+      }
+
+      shift = 8 - png_ptr->sig_bit.green;
+      if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
+      {
+         int component = png_ptr->palette[i].green;
+
+         component >>= shift;
+         png_ptr->palette[i].green = (png_byte)component;
+      }
+
+      shift = 8 - png_ptr->sig_bit.blue;
+      if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
+      {
+         int component = png_ptr->palette[i].blue;
+
+         component >>= shift;
+         png_ptr->palette[i].blue = (png_byte)component;
       }
    }
 #endif  /* PNG_READ_SHIFT_SUPPORTED */
- }
-#if !defined(PNG_READ_GAMMA_SUPPORTED) && !defined(PNG_READ_SHIFT_SUPPORTED) \
- && !defined(PNG_READ_BACKGROUND_SUPPORTED)
-   if (png_ptr)
-     return;
-#endif
 }
 
 /* Modify the info structure to reflect the transformations.  The
@@ -1034,132 +1879,196 @@
 void /* PRIVATE */
 png_read_transform_info(png_structp png_ptr, png_infop info_ptr)
 {
-   png_debug(1, "in png_read_transform_info\n");
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+   png_debug(1, "in png_read_transform_info");
+
+#ifdef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND)
    {
       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       {
-         if (png_ptr->num_trans)
+         /* This check must match what actually happens in
+          * png_do_expand_palette; if it ever checks the tRNS chunk to see if
+          * it is all opaque we must do the same (at present it does not.)
+          */
+         if (png_ptr->num_trans > 0)
             info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
+
          else
             info_ptr->color_type = PNG_COLOR_TYPE_RGB;
+
          info_ptr->bit_depth = 8;
          info_ptr->num_trans = 0;
       }
       else
       {
          if (png_ptr->num_trans)
-            info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
+         {
+            if (png_ptr->transformations & PNG_EXPAND_tRNS)
+               info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
+         }
          if (info_ptr->bit_depth < 8)
             info_ptr->bit_depth = 8;
+
          info_ptr->num_trans = 0;
       }
    }
 #endif
 
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-   if (png_ptr->transformations & PNG_BACKGROUND)
-   {
-      info_ptr->color_type &= ~PNG_COLOR_MASK_ALPHA;
-      info_ptr->num_trans = 0;
+#if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
+   defined(PNG_READ_ALPHA_MODE_SUPPORTED)
+   /* The following is almost certainly wrong unless the background value is in
+    * the screen space!
+    */
+   if (png_ptr->transformations & PNG_COMPOSE)
       info_ptr->background = png_ptr->background;
-   }
-#endif
-
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-   if (png_ptr->transformations & PNG_GAMMA)
-   {
-#ifdef PNG_FLOATING_POINT_SUPPORTED
-      info_ptr->gamma = png_ptr->gamma;
-#endif
-#ifdef PNG_FIXED_POINT_SUPPORTED
-      info_ptr->int_gamma = png_ptr->int_gamma;
-#endif
-   }
-#endif
-
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
-   if ((png_ptr->transformations & PNG_16_TO_8) && (info_ptr->bit_depth == 16))
-      info_ptr->bit_depth = 8;
-#endif
-
-#if defined(PNG_READ_DITHER_SUPPORTED)
-   if (png_ptr->transformations & PNG_DITHER)
+#endif
+
+#ifdef PNG_READ_GAMMA_SUPPORTED
+   /* The following used to be conditional on PNG_GAMMA (prior to 1.5.4),
+    * however it seems that the code in png_init_read_transformations, which has
+    * been called before this from png_read_update_info->png_read_start_row
+    * sometimes does the gamma transform and cancels the flag.
+    */
+   info_ptr->gamma = png_ptr->gamma;
+#endif
+
+   if (info_ptr->bit_depth == 16)
+   {
+#  ifdef PNG_READ_16BIT_SUPPORTED
+#     ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+         if (png_ptr->transformations & PNG_SCALE_16_TO_8)
+            info_ptr->bit_depth = 8;
+#     endif
+
+#     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+         if (png_ptr->transformations & PNG_16_TO_8)
+            info_ptr->bit_depth = 8;
+#     endif
+
+#  else
+      /* No 16 bit support: force chopping 16-bit input down to 8, in this case
+       * the app program can chose if both APIs are available by setting the
+       * correct scaling to use.
+       */
+#     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+         /* For compatibility with previous versions use the strip method by
+          * default.  This code works because if PNG_SCALE_16_TO_8 is already
+          * set the code below will do that in preference to the chop.
+          */
+         png_ptr->transformations |= PNG_16_TO_8;
+         info_ptr->bit_depth = 8;
+#     else
+
+#        ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+            png_ptr->transformations |= PNG_SCALE_16_TO_8;
+            info_ptr->bit_depth = 8;
+#        else
+
+            CONFIGURATION ERROR: you must enable at least one 16 to 8 method
+#        endif
+#    endif
+#endif /* !READ_16BIT_SUPPORTED */
+   }
+
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
+      info_ptr->color_type = (png_byte)(info_ptr->color_type |
+         PNG_COLOR_MASK_COLOR);
+#endif
+
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
+   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
+      info_ptr->color_type = (png_byte)(info_ptr->color_type &
+         ~PNG_COLOR_MASK_COLOR);
+#endif
+
+#ifdef PNG_READ_QUANTIZE_SUPPORTED
+   if (png_ptr->transformations & PNG_QUANTIZE)
    {
       if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
-         (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
-         png_ptr->palette_lookup && info_ptr->bit_depth == 8)
+          (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
+          png_ptr->palette_lookup && info_ptr->bit_depth == 8)
       {
          info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
       }
    }
 #endif
 
-#if defined(PNG_READ_PACK_SUPPORTED)
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+   if (png_ptr->transformations & PNG_EXPAND_16 && info_ptr->bit_depth == 8 &&
+      info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
+   {
+      info_ptr->bit_depth = 16;
+   }
+#endif
+
+#ifdef PNG_READ_PACK_SUPPORTED
    if ((png_ptr->transformations & PNG_PACK) && (info_ptr->bit_depth < 8))
       info_ptr->bit_depth = 8;
 #endif
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
-   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
-      info_ptr->color_type |= PNG_COLOR_MASK_COLOR;
-#endif
-
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
-   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
-      info_ptr->color_type &= ~PNG_COLOR_MASK_COLOR;
-#endif
-
    if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       info_ptr->channels = 1;
+
    else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
       info_ptr->channels = 3;
+
    else
       info_ptr->channels = 1;
 
-#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
-   if (png_ptr->flags & PNG_FLAG_STRIP_ALPHA)
-      info_ptr->color_type &= ~PNG_COLOR_MASK_ALPHA;
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
+   if (png_ptr->transformations & PNG_STRIP_ALPHA)
+   {
+      info_ptr->color_type = (png_byte)(info_ptr->color_type &
+         ~PNG_COLOR_MASK_ALPHA);
+      info_ptr->num_trans = 0;
+   }
 #endif
 
    if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
       info_ptr->channels++;
 
-#if defined(PNG_READ_FILLER_SUPPORTED)
+#ifdef PNG_READ_FILLER_SUPPORTED
    /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
    if ((png_ptr->transformations & PNG_FILLER) &&
        ((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
        (info_ptr->color_type == PNG_COLOR_TYPE_GRAY)))
    {
       info_ptr->channels++;
-      /* if adding a true alpha channel not just filler */
-#if !defined(PNG_1_0_X)
+      /* If adding a true alpha channel not just filler */
       if (png_ptr->transformations & PNG_ADD_ALPHA)
-      info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
-#endif
+         info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
    }
 #endif
 
 #if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
 defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
    if (png_ptr->transformations & PNG_USER_TRANSFORM)
-     {
-       if (info_ptr->bit_depth < png_ptr->user_transform_depth)
+   {
+      if (info_ptr->bit_depth < png_ptr->user_transform_depth)
          info_ptr->bit_depth = png_ptr->user_transform_depth;
-       if (info_ptr->channels < png_ptr->user_transform_channels)
+
+      if (info_ptr->channels < png_ptr->user_transform_channels)
          info_ptr->channels = png_ptr->user_transform_channels;
-     }
+   }
 #endif
 
    info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
-      info_ptr->bit_depth);
-
-   info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth,info_ptr->width);
-
-#if !defined(PNG_READ_EXPAND_SUPPORTED)
+       info_ptr->bit_depth);
+
+   info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);
+
+   /* Adding in 1.5.4: cache the above value in png_struct so that we can later
+    * check in png_rowbytes that the user buffer won't get overwritten.  Note
+    * that the field is not always set - if png_read_update_info isn't called
+    * the application has to either not do any transforms or get the calculation
+    * right itself.
+    */
+   png_ptr->info_rowbytes = info_ptr->rowbytes;
+
+#ifndef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr)
-     return;
+      return;
 #endif
 }
 
@@ -1168,231 +2077,297 @@
  * decide how it fits in with the other transformations here.
  */
 void /* PRIVATE */
-png_do_read_transformations(png_structp png_ptr)
+png_do_read_transformations(png_structp png_ptr, png_row_infop row_info)
 {
-   png_debug(1, "in png_do_read_transformations\n");
-#if !defined(PNG_USELESS_TESTS_SUPPORTED)
+   png_debug(1, "in png_do_read_transformations");
+
    if (png_ptr->row_buf == NULL)
    {
-#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
-      char msg[50];
-
-      sprintf(msg, "NULL row buffer for row %ld, pass %d", png_ptr->row_number,
-         png_ptr->pass);
-      png_error(png_ptr, msg);
-#else
+      /* Prior to 1.5.4 this output row/pass where the NULL pointer is, but this
+       * error is incredibly rare and incredibly easy to debug without this
+       * information.
+       */
       png_error(png_ptr, "NULL row buffer");
-#endif
-   }
-#endif
-
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+   }
+
+   /* The following is debugging; prior to 1.5.4 the code was never compiled in;
+    * in 1.5.4 PNG_FLAG_DETECT_UNINITIALIZED was added and the macro
+    * PNG_WARN_UNINITIALIZED_ROW removed.  In 1.5 the new flag is set only for
+    * selected new APIs to ensure that there is no API change.
+    */
+   if ((png_ptr->flags & PNG_FLAG_DETECT_UNINITIALIZED) != 0 &&
+      !(png_ptr->flags & PNG_FLAG_ROW_INIT))
+   {
+      /* Application has failed to call either png_read_start_image() or
+       * png_read_update_info() after setting transforms that expand pixels.
+       * This check added to libpng-1.2.19 (but not enabled until 1.5.4).
+       */
+      png_error(png_ptr, "Uninitialized row");
+   }
+
+#ifdef PNG_READ_EXPAND_SUPPORTED
    if (png_ptr->transformations & PNG_EXPAND)
    {
-      if (png_ptr->row_info.color_type == PNG_COLOR_TYPE_PALETTE)
-      {
-         png_do_expand_palette(&(png_ptr->row_info), png_ptr->row_buf + 1,
-            png_ptr->palette, png_ptr->trans, png_ptr->num_trans);
-      }
+      if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
+      {
+         png_do_expand_palette(row_info, png_ptr->row_buf + 1,
+             png_ptr->palette, png_ptr->trans_alpha, png_ptr->num_trans);
+      }
+
       else
       {
-         if (png_ptr->num_trans)
-            png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
-               &(png_ptr->trans_values));
+         if (png_ptr->num_trans &&
+             (png_ptr->transformations & PNG_EXPAND_tRNS))
+            png_do_expand(row_info, png_ptr->row_buf + 1,
+                &(png_ptr->trans_color));
+
          else
-            png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
-               NULL);
-      }
-   }
-#endif
-
-#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
-   if (png_ptr->flags & PNG_FLAG_STRIP_ALPHA)
-      png_do_strip_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
-         PNG_FLAG_FILLER_AFTER | (png_ptr->flags & PNG_FLAG_STRIP_ALPHA));
-#endif
-
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
+            png_do_expand(row_info, png_ptr->row_buf + 1,
+                NULL);
+      }
+   }
+#endif
+
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
+   if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
+      !(png_ptr->transformations & PNG_COMPOSE) &&
+      (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+      row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
+      png_do_strip_channel(row_info, png_ptr->row_buf + 1,
+         0 /* at_start == false, because SWAP_ALPHA happens later */);
+#endif
+
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    if (png_ptr->transformations & PNG_RGB_TO_GRAY)
    {
       int rgb_error =
-         png_do_rgb_to_gray(png_ptr, &(png_ptr->row_info), png_ptr->row_buf + 1);
+          png_do_rgb_to_gray(png_ptr, row_info,
+              png_ptr->row_buf + 1);
+
       if (rgb_error)
       {
          png_ptr->rgb_to_gray_status=1;
-         if (png_ptr->transformations == PNG_RGB_TO_GRAY_WARN)
-           png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
-         if (png_ptr->transformations == PNG_RGB_TO_GRAY_ERR)
-           png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
-      }
-   }
-#endif
-
-/*
-From Andreas Dilger e-mail to png-implement, 26 March 1998:
-
-  In most cases, the "simple transparency" should be done prior to doing
-  gray-to-RGB, or you will have to test 3x as many bytes to check if a
-  pixel is transparent.  You would also need to make sure that the
-  transparency information is upgraded to RGB.
-
-  To summarize, the current flow is:
-  - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
-                                  with background "in place" if transparent,
-                                  convert to RGB if necessary
-  - Gray + alpha -> composite with gray background and remove alpha bytes,
-                                  convert to RGB if necessary
-
-  To support RGB backgrounds for gray images we need:
-  - Gray + simple transparency -> convert to RGB + simple transparency, compare
-                                  3 or 6 bytes and composite with background
-                                  "in place" if transparent (3x compare/pixel
-                                  compared to doing composite with gray bkgrnd)
-  - Gray + alpha -> convert to RGB + alpha, composite with background and
-                                  remove alpha bytes (3x float operations/pixel
-                                  compared with composite on gray background)
-
-  Greg's change will do this.  The reason it wasn't done before is for
-  performance, as this increases the per-pixel operations.  If we would check
-  in advance if the background was gray or RGB, and position the gray-to-RGB
-  transform appropriately, then it would save a lot of work/time.
+         if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
+             PNG_RGB_TO_GRAY_WARN)
+            png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
+
+         if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
+             PNG_RGB_TO_GRAY_ERR)
+            png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
+      }
+   }
+#endif
+
+/* From Andreas Dilger e-mail to png-implement, 26 March 1998:
+ *
+ *   In most cases, the "simple transparency" should be done prior to doing
+ *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
+ *   pixel is transparent.  You would also need to make sure that the
+ *   transparency information is upgraded to RGB.
+ *
+ *   To summarize, the current flow is:
+ *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
+ *                                   with background "in place" if transparent,
+ *                                   convert to RGB if necessary
+ *   - Gray + alpha -> composite with gray background and remove alpha bytes,
+ *                                   convert to RGB if necessary
+ *
+ *   To support RGB backgrounds for gray images we need:
+ *   - Gray + simple transparency -> convert to RGB + simple transparency,
+ *                                   compare 3 or 6 bytes and composite with
+ *                                   background "in place" if transparent
+ *                                   (3x compare/pixel compared to doing
+ *                                   composite with gray bkgrnd)
+ *   - Gray + alpha -> convert to RGB + alpha, composite with background and
+ *                                   remove alpha bytes (3x float
+ *                                   operations/pixel compared with composite
+ *                                   on gray background)
+ *
+ *  Greg's change will do this.  The reason it wasn't done before is for
+ *  performance, as this increases the per-pixel operations.  If we would check
+ *  in advance if the background was gray or RGB, and position the gray-to-RGB
+ *  transform appropriately, then it would save a lot of work/time.
  */
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
-   /* if gray -> RGB, do so now only if background is non-gray; else do later
-    * for performance reasons */
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+   /* If gray -> RGB, do so now only if background is non-gray; else do later
+    * for performance reasons
+    */
    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
        !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
-      png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-   if ((png_ptr->transformations & PNG_BACKGROUND) &&
-      ((png_ptr->num_trans != 0 ) ||
-      (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)))
-      png_do_background(&(png_ptr->row_info), png_ptr->row_buf + 1,
-         &(png_ptr->trans_values), &(png_ptr->background)
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-         , &(png_ptr->background_1),
-         png_ptr->gamma_table, png_ptr->gamma_from_1,
-         png_ptr->gamma_to_1, png_ptr->gamma_16_table,
-         png_ptr->gamma_16_from_1, png_ptr->gamma_16_to_1,
-         png_ptr->gamma_shift
-#endif
-);
-#endif
-
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+      png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
+#endif
+
+#if (defined PNG_READ_BACKGROUND_SUPPORTED) ||\
+   (defined PNG_READ_ALPHA_MODE_SUPPORTED)
+   if (png_ptr->transformations & PNG_COMPOSE)
+      png_do_compose(row_info, png_ptr->row_buf + 1, png_ptr);
+#endif
+
+#ifdef PNG_READ_GAMMA_SUPPORTED
    if ((png_ptr->transformations & PNG_GAMMA) &&
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-      !((png_ptr->transformations & PNG_BACKGROUND) &&
-      ((png_ptr->num_trans != 0) ||
-      (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
-#endif
-      (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
-      png_do_gamma(&(png_ptr->row_info), png_ptr->row_buf + 1,
-         png_ptr->gamma_table, png_ptr->gamma_16_table,
-         png_ptr->gamma_shift);
-#endif
-
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
+      /* Because RGB_TO_GRAY does the gamma transform. */
+      !(png_ptr->transformations & PNG_RGB_TO_GRAY) &&
+#endif
+#if (defined PNG_READ_BACKGROUND_SUPPORTED) ||\
+   (defined PNG_READ_ALPHA_MODE_SUPPORTED)
+      /* Because PNG_COMPOSE does the gamma transform if there is something to
+       * do (if there is an alpha channel or transparency.)
+       */
+       !((png_ptr->transformations & PNG_COMPOSE) &&
+       ((png_ptr->num_trans != 0) ||
+       (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
+#endif
+      /* Because png_init_read_transformations transforms the palette, unless
+       * RGB_TO_GRAY will do the transform.
+       */
+       (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
+      png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
+#endif
+
+#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
+   if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
+      (png_ptr->transformations & PNG_COMPOSE) &&
+      (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+      row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
+      png_do_strip_channel(row_info, png_ptr->row_buf + 1,
+         0 /* at_start == false, because SWAP_ALPHA happens later */);
+#endif
+
+#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
+   if ((png_ptr->transformations & PNG_ENCODE_ALPHA) &&
+      (row_info->color_type & PNG_COLOR_MASK_ALPHA))
+      png_do_encode_alpha(row_info, png_ptr->row_buf + 1, png_ptr);
+#endif
+
+#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+   if (png_ptr->transformations & PNG_SCALE_16_TO_8)
+      png_do_scale_16_to_8(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+   /* There is no harm in doing both of these because only one has any effect,
+    * by putting the 'scale' option first if the app asks for scale (either by
+    * calling the API or in a TRANSFORM flag) this is what happens.
+    */
    if (png_ptr->transformations & PNG_16_TO_8)
-      png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_DITHER_SUPPORTED)
-   if (png_ptr->transformations & PNG_DITHER)
-   {
-      png_do_dither((png_row_infop)&(png_ptr->row_info), png_ptr->row_buf + 1,
-                    png_ptr->palette_lookup, png_ptr->dither_index);
-      if (png_ptr->row_info.rowbytes == (png_uint_32)0)
-        png_error(png_ptr, "png_do_dither returned rowbytes=0");
-   }
-#endif
-
-#if defined(PNG_READ_INVERT_SUPPORTED)
-   if (png_ptr->transformations & PNG_INVERT_MONO)
-      png_do_invert(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_SHIFT_SUPPORTED)
-   if (png_ptr->transformations & PNG_SHIFT)
-      png_do_unshift(&(png_ptr->row_info), png_ptr->row_buf + 1,
-         &(png_ptr->shift));
-#endif
-
-#if defined(PNG_READ_PACK_SUPPORTED)
-   if (png_ptr->transformations & PNG_PACK)
-      png_do_unpack(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_BGR_SUPPORTED)
-   if (png_ptr->transformations & PNG_BGR)
-      png_do_bgr(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_PACKSWAP_SUPPORTED)
-   if (png_ptr->transformations & PNG_PACKSWAP)
-      png_do_packswap(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
-   /* if gray -> RGB, do so now only if we did not do so above */
+      png_do_chop(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_QUANTIZE_SUPPORTED
+   if (png_ptr->transformations & PNG_QUANTIZE)
+   {
+      png_do_quantize(row_info, png_ptr->row_buf + 1,
+          png_ptr->palette_lookup, png_ptr->quantize_index);
+
+      if (row_info->rowbytes == 0)
+         png_error(png_ptr, "png_do_quantize returned rowbytes=0");
+   }
+#endif /* PNG_READ_QUANTIZE_SUPPORTED */
+
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+   /* Do the expansion now, after all the arithmetic has been done.  Notice
+    * that previous transformations can handle the PNG_EXPAND_16 flag if this
+    * is efficient (particularly true in the case of gamma correction, where
+    * better accuracy results faster!)
+    */
+   if (png_ptr->transformations & PNG_EXPAND_16)
+      png_do_expand_16(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+   /*NOTE: moved here in 1.5.4 (from much later in this list.) */
    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
        (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
-      png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_FILLER_SUPPORTED)
+      png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_INVERT_SUPPORTED
+   if (png_ptr->transformations & PNG_INVERT_MONO)
+      png_do_invert(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_SHIFT_SUPPORTED
+   if (png_ptr->transformations & PNG_SHIFT)
+      png_do_unshift(row_info, png_ptr->row_buf + 1,
+          &(png_ptr->shift));
+#endif
+
+#ifdef PNG_READ_PACK_SUPPORTED
+   if (png_ptr->transformations & PNG_PACK)
+      png_do_unpack(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
+   /* Added at libpng-1.5.10 */
+   if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
+      png_do_check_palette_indexes(png_ptr, row_info);
+#endif
+
+#ifdef PNG_READ_BGR_SUPPORTED
+   if (png_ptr->transformations & PNG_BGR)
+      png_do_bgr(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_PACKSWAP_SUPPORTED
+   if (png_ptr->transformations & PNG_PACKSWAP)
+      png_do_packswap(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_FILLER_SUPPORTED
    if (png_ptr->transformations & PNG_FILLER)
-      png_do_read_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
-         (png_uint_32)png_ptr->filler, png_ptr->flags);
-#endif
-
-#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
+      png_do_read_filler(row_info, png_ptr->row_buf + 1,
+          (png_uint_32)png_ptr->filler, png_ptr->flags);
+#endif
+
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_INVERT_ALPHA)
-      png_do_read_invert_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
+      png_do_read_invert_alpha(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
    if (png_ptr->transformations & PNG_SWAP_ALPHA)
-      png_do_read_swap_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_SWAP_SUPPORTED)
+      png_do_read_swap_alpha(row_info, png_ptr->row_buf + 1);
+#endif
+
+#ifdef PNG_READ_16BIT_SUPPORTED
+#ifdef PNG_READ_SWAP_SUPPORTED
    if (png_ptr->transformations & PNG_SWAP_BYTES)
-      png_do_swap(&(png_ptr->row_info), png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
+      png_do_swap(row_info, png_ptr->row_buf + 1);
+#endif
+#endif
+
+#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
    if (png_ptr->transformations & PNG_USER_TRANSFORM)
     {
       if (png_ptr->read_user_transform_fn != NULL)
-        (*(png_ptr->read_user_transform_fn)) /* user read transform function */
-          (png_ptr,                    /* png_ptr */
-           &(png_ptr->row_info),       /* row_info:     */
-             /*  png_uint_32 width;          width of row */
-             /*  png_uint_32 rowbytes;       number of bytes in row */
-             /*  png_byte color_type;        color type of pixels */
-             /*  png_byte bit_depth;         bit depth of samples */
-             /*  png_byte channels;          number of channels (1-4) */
-             /*  png_byte pixel_depth;       bits per pixel (depth*channels) */
-           png_ptr->row_buf + 1);      /* start of pixel data for row */
-#if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
+         (*(png_ptr->read_user_transform_fn)) /* User read transform function */
+             (png_ptr,     /* png_ptr */
+             row_info,     /* row_info: */
+                /*  png_uint_32 width;       width of row */
+                /*  png_size_t rowbytes;     number of bytes in row */
+                /*  png_byte color_type;     color type of pixels */
+                /*  png_byte bit_depth;      bit depth of samples */
+                /*  png_byte channels;       number of channels (1-4) */
+                /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
+             png_ptr->row_buf + 1);    /* start of pixel data for row */
+#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
       if (png_ptr->user_transform_depth)
-        png_ptr->row_info.bit_depth = png_ptr->user_transform_depth;
+         row_info->bit_depth = png_ptr->user_transform_depth;
+
       if (png_ptr->user_transform_channels)
-        png_ptr->row_info.channels = png_ptr->user_transform_channels;
-#endif
-      png_ptr->row_info.pixel_depth = (png_byte)(png_ptr->row_info.bit_depth *
-         png_ptr->row_info.channels);
-      png_ptr->row_info.rowbytes = PNG_ROWBYTES(png_ptr->row_info.pixel_depth,
-         png_ptr->row_info.width);
+         row_info->channels = png_ptr->user_transform_channels;
+#endif
+      row_info->pixel_depth = (png_byte)(row_info->bit_depth *
+          row_info->channels);
+
+      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_info->width);
    }
 #endif
 }
 
-#if defined(PNG_READ_PACK_SUPPORTED)
+#ifdef PNG_READ_PACK_SUPPORTED
 /* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
  * without changing the actual values.  Thus, if you had a row with
  * a bit depth of 1, you would end up with bytes that only contained
@@ -1402,12 +2377,9 @@
 void /* PRIVATE */
 png_do_unpack(png_row_infop row_info, png_bytep row)
 {
-   png_debug(1, "in png_do_unpack\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (row != NULL && row_info != NULL && row_info->bit_depth < 8)
-#else
+   png_debug(1, "in png_do_unpack");
+
    if (row_info->bit_depth < 8)
-#endif
    {
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;
@@ -1422,11 +2394,13 @@
             for (i = 0; i < row_width; i++)
             {
                *dp = (png_byte)((*sp >> shift) & 0x01);
+
                if (shift == 7)
                {
                   shift = 0;
                   sp--;
                }
+
                else
                   shift++;
 
@@ -1434,19 +2408,23 @@
             }
             break;
          }
+
          case 2:
          {
+
             png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
             png_bytep dp = row + (png_size_t)row_width - 1;
             png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
             for (i = 0; i < row_width; i++)
             {
                *dp = (png_byte)((*sp >> shift) & 0x03);
+
                if (shift == 6)
                {
                   shift = 0;
                   sp--;
                }
+
                else
                   shift += 2;
 
@@ -1454,6 +2432,7 @@
             }
             break;
          }
+
          case 4:
          {
             png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
@@ -1462,11 +2441,13 @@
             for (i = 0; i < row_width; i++)
             {
                *dp = (png_byte)((*sp >> shift) & 0x0f);
+
                if (shift == 4)
                {
                   shift = 0;
                   sp--;
                }
+
                else
                   shift = 4;
 
@@ -1474,6 +2455,9 @@
             }
             break;
          }
+
+         default:
+            break;
       }
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
@@ -1482,164 +2466,201 @@
 }
 #endif
 
-#if defined(PNG_READ_SHIFT_SUPPORTED)
+#ifdef PNG_READ_SHIFT_SUPPORTED
 /* Reverse the effects of png_do_shift.  This routine merely shifts the
  * pixels back to their significant bits values.  Thus, if you have
  * a row of bit depth 8, but only 5 are significant, this will shift
  * the values back to 0 through 31.
  */
 void /* PRIVATE */
-png_do_unshift(png_row_infop row_info, png_bytep row, png_color_8p sig_bits)
+png_do_unshift(png_row_infop row_info, png_bytep row,
+    png_const_color_8p sig_bits)
 {
-   png_debug(1, "in png_do_unshift\n");
-   if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL && sig_bits != NULL &&
-#endif
-       row_info->color_type != PNG_COLOR_TYPE_PALETTE)
+   int color_type;
+
+   png_debug(1, "in png_do_unshift");
+
+   /* The palette case has already been handled in the _init routine. */
+   color_type = row_info->color_type;
+
+   if (color_type != PNG_COLOR_TYPE_PALETTE)
    {
       int shift[4];
       int channels = 0;
-      int c;
-      png_uint_16 value = 0;
-      png_uint_32 row_width = row_info->width;
-
-      if (row_info->color_type & PNG_COLOR_MASK_COLOR)
-      {
-         shift[channels++] = row_info->bit_depth - sig_bits->red;
-         shift[channels++] = row_info->bit_depth - sig_bits->green;
-         shift[channels++] = row_info->bit_depth - sig_bits->blue;
-      }
+      int bit_depth = row_info->bit_depth;
+
+      if (color_type & PNG_COLOR_MASK_COLOR)
+      {
+         shift[channels++] = bit_depth - sig_bits->red;
+         shift[channels++] = bit_depth - sig_bits->green;
+         shift[channels++] = bit_depth - sig_bits->blue;
+      }
+
       else
       {
-         shift[channels++] = row_info->bit_depth - sig_bits->gray;
-      }
-      if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
-      {
-         shift[channels++] = row_info->bit_depth - sig_bits->alpha;
-      }
-
-      for (c = 0; c < channels; c++)
-      {
-         if (shift[c] <= 0)
-            shift[c] = 0;
-         else
-            value = 1;
-      }
-
-      if (!value)
-         return;
-
-      switch (row_info->bit_depth)
-      {
+         shift[channels++] = bit_depth - sig_bits->gray;
+      }
+
+      if (color_type & PNG_COLOR_MASK_ALPHA)
+      {
+         shift[channels++] = bit_depth - sig_bits->alpha;
+      }
+
+      {
+         int c, have_shift;
+
+         for (c = have_shift = 0; c < channels; ++c)
+         {
+            /* A shift of more than the bit depth is an error condition but it
+             * gets ignored here.
+             */
+            if (shift[c] <= 0 || shift[c] >= bit_depth)
+               shift[c] = 0;
+
+            else
+               have_shift = 1;
+         }
+
+         if (!have_shift)
+            return;
+      }
+
+      switch (bit_depth)
+      {
+         default:
+         /* Must be 1bpp gray: should not be here! */
+            /* NOTREACHED */
+            break;
+
          case 2:
-         {
-            png_bytep bp;
-            png_uint_32 i;
-            png_uint_32 istop = row_info->rowbytes;
-
-            for (bp = row, i = 0; i < istop; i++)
-            {
-               *bp >>= 1;
-               *bp++ &= 0x55;
+         /* Must be 2bpp gray */
+         /* assert(channels == 1 && shift[0] == 1) */
+         {
+            png_bytep bp = row;
+            png_bytep bp_end = bp + row_info->rowbytes;
+
+            while (bp < bp_end)
+            {
+               int b = (*bp >> 1) & 0x55;
+               *bp++ = (png_byte)b;
             }
             break;
          }
+
          case 4:
+         /* Must be 4bpp gray */
+         /* assert(channels == 1) */
          {
             png_bytep bp = row;
-            png_uint_32 i;
-            png_uint_32 istop = row_info->rowbytes;
-            png_byte mask = (png_byte)((((int)0xf0 >> shift[0]) & (int)0xf0) |
-               (png_byte)((int)0xf >> shift[0]));
-
-            for (i = 0; i < istop; i++)
-            {
-               *bp >>= shift[0];
-               *bp++ &= mask;
+            png_bytep bp_end = bp + row_info->rowbytes;
+            int gray_shift = shift[0];
+            int mask =  0xf >> gray_shift;
+
+            mask |= mask << 4;
+
+            while (bp < bp_end)
+            {
+               int b = (*bp >> gray_shift) & mask;
+               *bp++ = (png_byte)b;
             }
             break;
          }
+
          case 8:
+         /* Single byte components, G, GA, RGB, RGBA */
          {
             png_bytep bp = row;
-            png_uint_32 i;
-            png_uint_32 istop = row_width * channels;
-
-            for (i = 0; i < istop; i++)
-            {
-               *bp++ >>= shift[i%channels];
+            png_bytep bp_end = bp + row_info->rowbytes;
+            int channel = 0;
+
+            while (bp < bp_end)
+            {
+               int b = *bp >> shift[channel];
+               if (++channel >= channels)
+                  channel = 0;
+               *bp++ = (png_byte)b;
             }
             break;
          }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
          case 16:
+         /* Double byte components, G, GA, RGB, RGBA */
          {
             png_bytep bp = row;
-            png_uint_32 i;
-            png_uint_32 istop = channels * row_width;
-
-            for (i = 0; i < istop; i++)
-            {
-               value = (png_uint_16)((*bp << 8) + *(bp + 1));
-               value >>= shift[i%channels];
+            png_bytep bp_end = bp + row_info->rowbytes;
+            int channel = 0;
+
+            while (bp < bp_end)
+            {
+               int value = (bp[0] << 8) + bp[1];
+
+               value >>= shift[channel];
+               if (++channel >= channels)
+                  channel = 0;
                *bp++ = (png_byte)(value >> 8);
                *bp++ = (png_byte)(value & 0xff);
             }
             break;
          }
+#endif
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_16_TO_8_SUPPORTED)
-/* chop rows of bit depth 16 down to 8 */
+#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
+/* Scale rows of bit depth 16 down to 8 accurately */
 void /* PRIVATE */
-png_do_chop(png_row_infop row_info, png_bytep row)
+png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
 {
-   png_debug(1, "in png_do_chop\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (row != NULL && row_info != NULL && row_info->bit_depth == 16)
-#else
+   png_debug(1, "in png_do_scale_16_to_8");
+
    if (row_info->bit_depth == 16)
-#endif
-   {
-      png_bytep sp = row;
-      png_bytep dp = row;
-      png_uint_32 i;
-      png_uint_32 istop = row_info->width * row_info->channels;
-
-      for (i = 0; i<istop; i++, sp += 2, dp++)
-      {
-#if defined(PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED)
-      /* This does a more accurate scaling of the 16-bit color
-       * value, rather than a simple low-byte truncation.
-       *
-       * What the ideal calculation should be:
-       *   *dp = (((((png_uint_32)(*sp) << 8) |
-       *          (png_uint_32)(*(sp + 1))) * 255 + 127) / (png_uint_32)65535L;
-       *
-       * GRR: no, I think this is what it really should be:
-       *   *dp = (((((png_uint_32)(*sp) << 8) |
-       *           (png_uint_32)(*(sp + 1))) + 128L) / (png_uint_32)257L;
-       *
-       * GRR: here's the exact calculation with shifts:
-       *   temp = (((png_uint_32)(*sp) << 8) | (png_uint_32)(*(sp + 1))) + 128L;
-       *   *dp = (temp - (temp >> 8)) >> 8;
-       *
-       * Approximate calculation with shift/add instead of multiply/divide:
-       *   *dp = ((((png_uint_32)(*sp) << 8) |
-       *          (png_uint_32)((int)(*(sp + 1)) - *sp)) + 128) >> 8;
-       *
-       * What we actually do to avoid extra shifting and conversion:
-       */
-
-         *dp = *sp + ((((int)(*(sp + 1)) - *sp) > 128) ? 1 : 0);
-#else
-       /* Simply discard the low order byte */
-         *dp = *sp;
-#endif
-      }
+   {
+      png_bytep sp = row; /* source */
+      png_bytep dp = row; /* destination */
+      png_bytep ep = sp + row_info->rowbytes; /* end+1 */
+
+      while (sp < ep)
+      {
+         /* The input is an array of 16 bit components, these must be scaled to
+          * 8 bits each.  For a 16 bit value V the required value (from the PNG
+          * specification) is:
+          *
+          *    (V * 255) / 65535
+          *
+          * This reduces to round(V / 257), or floor((V + 128.5)/257)
+          *
+          * Represent V as the two byte value vhi.vlo.  Make a guess that the
+          * result is the top byte of V, vhi, then the correction to this value
+          * is:
+          *
+          *    error = floor(((V-vhi.vhi) + 128.5) / 257)
+          *          = floor(((vlo-vhi) + 128.5) / 257)
+          *
+          * This can be approximated using integer arithmetic (and a signed
+          * shift):
+          *
+          *    error = (vlo-vhi+128) >> 8;
+          *
+          * The approximate differs from the exact answer only when (vlo-vhi) is
+          * 128; it then gives a correction of +1 when the exact correction is
+          * 0.  This gives 128 errors.  The exact answer (correct for all 16 bit
+          * input values) is:
+          *
+          *    error = (vlo-vhi+128)*65535 >> 24;
+          *
+          * An alternative arithmetic calculation which also gives no errors is:
+          *
+          *    (V * 255 + 32895) >> 16
+          */
+
+         png_int_32 tmp = *sp++; /* must be signed! */
+         tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
+         *dp++ = (png_byte)tmp;
+      }
+
       row_info->bit_depth = 8;
       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
       row_info->rowbytes = row_info->width * row_info->channels;
@@ -1647,14 +2668,40 @@
 }
 #endif
 
-#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
+#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
+void /* PRIVATE */
+/* Simply discard the low byte.  This was the default behavior prior
+ * to libpng-1.5.4.
+ */
+png_do_chop(png_row_infop row_info, png_bytep row)
+{
+   png_debug(1, "in png_do_chop");
+
+   if (row_info->bit_depth == 16)
+   {
+      png_bytep sp = row; /* source */
+      png_bytep dp = row; /* destination */
+      png_bytep ep = sp + row_info->rowbytes; /* end+1 */
+
+      while (sp < ep)
+      {
+         *dp++ = *sp;
+         sp += 2; /* skip low byte */
+      }
+
+      row_info->bit_depth = 8;
+      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
+      row_info->rowbytes = row_info->width * row_info->channels;
+   }
+}
+#endif
+
+#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
 void /* PRIVATE */
 png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
 {
-   png_debug(1, "in png_do_read_swap_alpha\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (row != NULL && row_info != NULL)
-#endif
+   png_debug(1, "in png_do_read_swap_alpha");
+
    {
       png_uint_32 row_width = row_info->width;
       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
@@ -1676,6 +2723,8 @@
                *(--dp) = save;
             }
          }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
          /* This converts from RRGGBBAA to AARRGGBB */
          else
          {
@@ -1698,7 +2747,9 @@
                *(--dp) = save[1];
             }
          }
-      }
+#endif
+      }
+
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
       {
          /* This converts from GA to AG */
@@ -1716,6 +2767,8 @@
                *(--dp) = save;
             }
          }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
          /* This converts from GGAA to AAGG */
          else
          {
@@ -1734,133 +2787,137 @@
                *(--dp) = save[1];
             }
          }
+#endif
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
+#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
 void /* PRIVATE */
 png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
 {
-   png_debug(1, "in png_do_read_invert_alpha\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (row != NULL && row_info != NULL)
-#endif
-   {
-      png_uint_32 row_width = row_info->width;
-      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
+   png_uint_32 row_width;
+   png_debug(1, "in png_do_read_invert_alpha");
+
+   row_width = row_info->width;
+   if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
+   {
+      if (row_info->bit_depth == 8)
       {
          /* This inverts the alpha channel in RGBA */
-         if (row_info->bit_depth == 8)
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = (png_byte)(255 - *(--sp));
-
-/*             This does nothing:
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               We can replace it with:
+         png_bytep sp = row + row_info->rowbytes;
+         png_bytep dp = sp;
+         png_uint_32 i;
+
+         for (i = 0; i < row_width; i++)
+         {
+            *(--dp) = (png_byte)(255 - *(--sp));
+
+/*          This does nothing:
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            We can replace it with:
 */
-               sp-=3;
-               dp=sp;
-            }
-         }
-         /* This inverts the alpha channel in RRGGBBAA */
-         else
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = (png_byte)(255 - *(--sp));
-               *(--dp) = (png_byte)(255 - *(--sp));
-
-/*             This does nothing:
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               We can replace it with:
+            sp-=3;
+            dp=sp;
+         }
+      }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
+      /* This inverts the alpha channel in RRGGBBAA */
+      else
+      {
+         png_bytep sp = row + row_info->rowbytes;
+         png_bytep dp = sp;
+         png_uint_32 i;
+
+         for (i = 0; i < row_width; i++)
+         {
+            *(--dp) = (png_byte)(255 - *(--sp));
+            *(--dp) = (png_byte)(255 - *(--sp));
+
+/*          This does nothing:
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            We can replace it with:
 */
-               sp-=6;
-               dp=sp;
-            }
-         }
-      }
-      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
+            sp-=6;
+            dp=sp;
+         }
+      }
+#endif
+   }
+   else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
+   {
+      if (row_info->bit_depth == 8)
       {
          /* This inverts the alpha channel in GA */
-         if (row_info->bit_depth == 8)
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = (png_byte)(255 - *(--sp));
-               *(--dp) = *(--sp);
-            }
-         }
+         png_bytep sp = row + row_info->rowbytes;
+         png_bytep dp = sp;
+         png_uint_32 i;
+
+         for (i = 0; i < row_width; i++)
+         {
+            *(--dp) = (png_byte)(255 - *(--sp));
+            *(--dp) = *(--sp);
+         }
+      }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
+      else
+      {
          /* This inverts the alpha channel in GGAA */
-         else
-         {
-            png_bytep sp  = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = (png_byte)(255 - *(--sp));
-               *(--dp) = (png_byte)(255 - *(--sp));
+         png_bytep sp  = row + row_info->rowbytes;
+         png_bytep dp = sp;
+         png_uint_32 i;
+
+         for (i = 0; i < row_width; i++)
+         {
+            *(--dp) = (png_byte)(255 - *(--sp));
+            *(--dp) = (png_byte)(255 - *(--sp));
 /*
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
+            *(--dp) = *(--sp);
 */
-               sp-=2;
-               dp=sp;
-            }
-         }
-      }
+            sp-=2;
+            dp=sp;
+         }
+      }
+#endif
    }
 }
 #endif
 
-#if defined(PNG_READ_FILLER_SUPPORTED)
+#ifdef PNG_READ_FILLER_SUPPORTED
 /* Add filler channel if we have RGB color */
 void /* PRIVATE */
 png_do_read_filler(png_row_infop row_info, png_bytep row,
-                   png_uint_32 filler, png_uint_32 flags)
+    png_uint_32 filler, png_uint_32 flags)
 {
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
 
+#ifdef PNG_READ_16BIT_SUPPORTED
    png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
+#endif
    png_byte lo_filler = (png_byte)(filler & 0xff);
 
-   png_debug(1, "in png_do_read_filler\n");
+   png_debug(1, "in png_do_read_filler");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL  && row_info != NULL &&
-#endif
        row_info->color_type == PNG_COLOR_TYPE_GRAY)
    {
       if (row_info->bit_depth == 8)
       {
-         /* This changes the data from G to GX */
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
+            /* This changes the data from G to GX */
             png_bytep sp = row + (png_size_t)row_width;
             png_bytep dp =  sp + (png_size_t)row_width;
             for (i = 1; i < row_width; i++)
@@ -1873,9 +2930,10 @@
             row_info->pixel_depth = 16;
             row_info->rowbytes = row_width * 2;
          }
-      /* This changes the data from G to XG */
+
          else
          {
+            /* This changes the data from G to XG */
             png_bytep sp = row + (png_size_t)row_width;
             png_bytep dp = sp  + (png_size_t)row_width;
             for (i = 0; i < row_width; i++)
@@ -1888,11 +2946,13 @@
             row_info->rowbytes = row_width * 2;
          }
       }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
       else if (row_info->bit_depth == 16)
       {
-         /* This changes the data from GG to GGXX */
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
+            /* This changes the data from GG to GGXX */
             png_bytep sp = row + (png_size_t)row_width * 2;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 1; i < row_width; i++)
@@ -1908,9 +2968,10 @@
             row_info->pixel_depth = 32;
             row_info->rowbytes = row_width * 4;
          }
-         /* This changes the data from GG to XXGG */
+
          else
          {
+            /* This changes the data from GG to XXGG */
             png_bytep sp = row + (png_size_t)row_width * 2;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
@@ -1925,14 +2986,15 @@
             row_info->rowbytes = row_width * 4;
          }
       }
+#endif
    } /* COLOR_TYPE == GRAY */
    else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
    {
       if (row_info->bit_depth == 8)
       {
-         /* This changes the data from RGB to RGBX */
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
+            /* This changes the data from RGB to RGBX */
             png_bytep sp = row + (png_size_t)row_width * 3;
             png_bytep dp = sp  + (png_size_t)row_width;
             for (i = 1; i < row_width; i++)
@@ -1947,9 +3009,10 @@
             row_info->pixel_depth = 32;
             row_info->rowbytes = row_width * 4;
          }
-      /* This changes the data from RGB to XRGB */
+
          else
          {
+            /* This changes the data from RGB to XRGB */
             png_bytep sp = row + (png_size_t)row_width * 3;
             png_bytep dp = sp + (png_size_t)row_width;
             for (i = 0; i < row_width; i++)
@@ -1964,11 +3027,13 @@
             row_info->rowbytes = row_width * 4;
          }
       }
+
+#ifdef PNG_READ_16BIT_SUPPORTED
       else if (row_info->bit_depth == 16)
       {
-         /* This changes the data from RRGGBB to RRGGBBXX */
          if (flags & PNG_FLAG_FILLER_AFTER)
          {
+            /* This changes the data from RRGGBB to RRGGBBXX */
             png_bytep sp = row + (png_size_t)row_width * 6;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 1; i < row_width; i++)
@@ -1988,9 +3053,10 @@
             row_info->pixel_depth = 64;
             row_info->rowbytes = row_width * 8;
          }
-         /* This changes the data from RRGGBB to XXRRGGBB */
+
          else
          {
+            /* This changes the data from RRGGBB to XXRRGGBB */
             png_bytep sp = row + (png_size_t)row_width * 6;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
@@ -2004,34 +3070,35 @@
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
             }
+
             row_info->channels = 4;
             row_info->pixel_depth = 64;
             row_info->rowbytes = row_width * 8;
          }
       }
+#endif
    } /* COLOR_TYPE == RGB */
 }
 #endif
 
-#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
-/* expand grayscale files to RGB, with or without alpha */
+#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
+/* Expand grayscale files to RGB, with or without alpha */
 void /* PRIVATE */
 png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
 {
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
 
-   png_debug(1, "in png_do_gray_to_rgb\n");
+   png_debug(1, "in png_do_gray_to_rgb");
+
    if (row_info->bit_depth >= 8 &&
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL &&
-#endif
-      !(row_info->color_type & PNG_COLOR_MASK_COLOR))
+       !(row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          if (row_info->bit_depth == 8)
          {
+            /* This changes G to RGB */
             png_bytep sp = row + (png_size_t)row_width - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
@@ -2041,8 +3108,10 @@
                *(dp--) = *(sp--);
             }
          }
+
          else
          {
+            /* This changes GG to RRGGBB */
             png_bytep sp = row + (png_size_t)row_width * 2 - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 4;
             for (i = 0; i < row_width; i++)
@@ -2056,10 +3125,12 @@
             }
          }
       }
+
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
       {
          if (row_info->bit_depth == 8)
          {
+            /* This changes GA to RGBA */
             png_bytep sp = row + (png_size_t)row_width * 2 - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 2;
             for (i = 0; i < row_width; i++)
@@ -2070,8 +3141,10 @@
                *(dp--) = *(sp--);
             }
          }
+
          else
          {
+            /* This changes GGAA to RRGGBBAA */
             png_bytep sp = row + (png_size_t)row_width * 4 - 1;
             png_bytep dp = sp  + (png_size_t)row_width * 4;
             for (i = 0; i < row_width; i++)
@@ -2087,272 +3160,269 @@
             }
          }
       }
-      row_info->channels += (png_byte)2;
+      row_info->channels = (png_byte)(row_info->channels + 2);
       row_info->color_type |= PNG_COLOR_MASK_COLOR;
       row_info->pixel_depth = (png_byte)(row_info->channels *
-         row_info->bit_depth);
-      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,row_width);
+          row_info->bit_depth);
+      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
    }
 }
 #endif
 
-#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
-/* reduce RGB files to grayscale, with or without alpha
- * using the equation given in Poynton's ColorFAQ at
- * <http://www.inforamp.net/~poynton/>
- * Copyright (c) 1998-01-04 Charles Poynton poynton�inforamp.net
+#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
+/* Reduce RGB files to grayscale, with or without alpha
+ * using the equation given in Poynton's ColorFAQ of 1998-01-04 at
+ * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008 but
+ * versions dated 1998 through November 2002 have been archived at
+ * http://web.archive.org/web/20000816232553/http://www.inforamp.net/
+ * ~poynton/notes/colour_and_gamma/ColorFAQ.txt )
+ * Charles Poynton poynton at poynton.com
  *
  *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
- *
- *  We approximate this with
- *
- *     Y = 0.21268 * R    + 0.7151 * G    + 0.07217 * B
  *
  *  which can be expressed with integers as
  *
  *     Y = (6969 * R + 23434 * G + 2365 * B)/32768
  *
- *  The calculation is to be done in a linear colorspace.
+ * Poynton's current link (as of January 2003 through July 2011):
+ * <http://www.poynton.com/notes/colour_and_gamma/>
+ * has changed the numbers slightly:
  *
- *  Other integer coefficients can be used via png_set_rgb_to_gray().
+ *     Y = 0.2126*R + 0.7152*G + 0.0722*B
+ *
+ *  which can be expressed with integers as
+ *
+ *     Y = (6966 * R + 23436 * G + 2366 * B)/32768
+ *
+ *  Historically, however, libpng uses numbers derived from the ITU-R Rec 709
+ *  end point chromaticities and the D65 white point.  Depending on the
+ *  precision used for the D65 white point this produces a variety of different
+ *  numbers, however if the four decimal place value used in ITU-R Rec 709 is
+ *  used (0.3127,0.3290) the Y calculation would be:
+ *
+ *     Y = (6968 * R + 23435 * G + 2366 * B)/32768
+ *
+ *  While this is correct the rounding results in an overflow for white, because
+ *  the sum of the rounded coefficients is 32769, not 32768.  Consequently
+ *  libpng uses, instead, the closest non-overflowing approximation:
+ *
+ *     Y = (6968 * R + 23434 * G + 2366 * B)/32768
+ *
+ *  Starting with libpng-1.5.5, if the image being converted has a cHRM chunk
+ *  (including an sRGB chunk) then the chromaticities are used to calculate the
+ *  coefficients.  See the chunk handling in pngrutil.c for more information.
+ *
+ *  In all cases the calculation is to be done in a linear colorspace.  If no
+ *  gamma information is available to correct the encoding of the original RGB
+ *  values this results in an implicit assumption that the original PNG RGB
+ *  values were linear.
+ *
+ *  Other integer coefficents can be used via png_set_rgb_to_gray().  Because
+ *  the API takes just red and green coefficients the blue coefficient is
+ *  calculated to make the sum 32768.  This will result in different rounding
+ *  to that used above.
  */
 int /* PRIVATE */
 png_do_rgb_to_gray(png_structp png_ptr, png_row_infop row_info, png_bytep row)
+
 {
-   png_uint_32 i;
-
-   png_uint_32 row_width = row_info->width;
    int rgb_error = 0;
 
-   png_debug(1, "in png_do_rgb_to_gray\n");
-   if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL &&
-#endif
-      (row_info->color_type & PNG_COLOR_MASK_COLOR))
-   {
-      png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
-      png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
-      png_uint_32 bc = png_ptr->rgb_to_gray_blue_coeff;
-
-      if (row_info->color_type == PNG_COLOR_TYPE_RGB)
-      {
-         if (row_info->bit_depth == 8)
-         {
+   png_debug(1, "in png_do_rgb_to_gray");
+
+   if (!(row_info->color_type & PNG_COLOR_MASK_PALETTE) &&
+       (row_info->color_type & PNG_COLOR_MASK_COLOR))
+   {
+      PNG_CONST png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
+      PNG_CONST png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
+      PNG_CONST png_uint_32 bc = 32768 - rc - gc;
+      PNG_CONST png_uint_32 row_width = row_info->width;
+      PNG_CONST int have_alpha =
+         (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
+
+      if (row_info->bit_depth == 8)
+      {
 #if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
-            if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-
-               for (i = 0; i < row_width; i++)
-               {
-                  png_byte red   = png_ptr->gamma_to_1[*(sp++)];
-                  png_byte green = png_ptr->gamma_to_1[*(sp++)];
-                  png_byte blue  = png_ptr->gamma_to_1[*(sp++)];
-                  if (red != green || red != blue)
-                  {
-                     rgb_error |= 1;
-                     *(dp++) = png_ptr->gamma_from_1[
-                       (rc*red+gc*green+bc*blue)>>15];
-                  }
+         /* Notice that gamma to/from 1 are not necessarily inverses (if
+          * there is an overall gamma correction).  Prior to 1.5.5 this code
+          * checked the linearized values for equality; this doesn't match
+          * the documentation, the original values must be checked.
+          */
+         if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
+         {
+            png_bytep sp = row;
+            png_bytep dp = row;
+            png_uint_32 i;
+
+            for (i = 0; i < row_width; i++)
+            {
+               png_byte red   = *(sp++);
+               png_byte green = *(sp++);
+               png_byte blue  = *(sp++);
+
+               if (red != green || red != blue)
+               {
+                  red = png_ptr->gamma_to_1[red];
+                  green = png_ptr->gamma_to_1[green];
+                  blue = png_ptr->gamma_to_1[blue];
+
+                  rgb_error |= 1;
+                  *(dp++) = png_ptr->gamma_from_1[
+                      (rc*red + gc*green + bc*blue + 16384)>>15];
+               }
+
+               else
+               {
+                  /* If there is no overall correction the table will not be
+                   * set.
+                   */
+                  if (png_ptr->gamma_table != NULL)
+                     red = png_ptr->gamma_table[red];
+
+                  *(dp++) = red;
+               }
+
+               if (have_alpha)
+                  *(dp++) = *(sp++);
+            }
+         }
+         else
+#endif
+         {
+            png_bytep sp = row;
+            png_bytep dp = row;
+            png_uint_32 i;
+
+            for (i = 0; i < row_width; i++)
+            {
+               png_byte red   = *(sp++);
+               png_byte green = *(sp++);
+               png_byte blue  = *(sp++);
+
+               if (red != green || red != blue)
+               {
+                  rgb_error |= 1;
+                  /*NOTE: this is the historical approach which simply
+                   * truncates the results.
+                   */
+                  *(dp++) = (png_byte)((rc*red + gc*green + bc*blue)>>15);
+               }
+
+               else
+                  *(dp++) = red;
+
+               if (have_alpha)
+                  *(dp++) = *(sp++);
+            }
+         }
+      }
+
+      else /* RGB bit_depth == 16 */
+      {
+#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
+         if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
+         {
+            png_bytep sp = row;
+            png_bytep dp = row;
+            png_uint_32 i;
+
+            for (i = 0; i < row_width; i++)
+            {
+               png_uint_16 red, green, blue, w;
+
+               red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
+               green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
+               blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
+
+               if (red == green && red == blue)
+               {
+                  if (png_ptr->gamma_16_table != NULL)
+                     w = png_ptr->gamma_16_table[(red&0xff)
+                         >> png_ptr->gamma_shift][red>>8];
+
                   else
-                     *(dp++) = *(sp-1);
-               }
-            }
-            else
-#endif
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_byte red   = *(sp++);
-                  png_byte green = *(sp++);
-                  png_byte blue  = *(sp++);
-                  if (red != green || red != blue)
-                  {
-                     rgb_error |= 1;
-                     *(dp++) = (png_byte)((rc*red+gc*green+bc*blue)>>15);
-                  }
-                  else
-                     *(dp++) = *(sp-1);
-               }
-            }
-         }
-
-         else /* RGB bit_depth == 16 */
-         {
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
-            if (png_ptr->gamma_16_to_1 != NULL &&
-                png_ptr->gamma_16_from_1 != NULL)
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 red, green, blue, w;
-
-                  red   = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-                  green = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-                  blue  = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-
-                  if (red == green && red == blue)
                      w = red;
-                  else
-                  {
-                     png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff) >>
-                                  png_ptr->gamma_shift][red>>8];
-                     png_uint_16 green_1 = png_ptr->gamma_16_to_1[(green&0xff) >>
-                                  png_ptr->gamma_shift][green>>8];
-                     png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff) >>
-                                  png_ptr->gamma_shift][blue>>8];
-                     png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
-                                  + bc*blue_1)>>15);
-                     w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
-                         png_ptr->gamma_shift][gray16 >> 8];
-                     rgb_error |= 1;
-                  }
-
-                  *(dp++) = (png_byte)((w>>8) & 0xff);
-                  *(dp++) = (png_byte)(w & 0xff);
-               }
-            }
-            else
-#endif
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 red, green, blue, gray16;
-
-                  red   = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-                  green = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-                  blue  = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-
-                  if (red != green || red != blue)
-                    rgb_error |= 1;
-                  gray16  = (png_uint_16)((rc*red + gc*green + bc*blue)>>15);
-                  *(dp++) = (png_byte)((gray16>>8) & 0xff);
-                  *(dp++) = (png_byte)(gray16 & 0xff);
-               }
-            }
-         }
-      }
-      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
-      {
-         if (row_info->bit_depth == 8)
-         {
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
-            if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_byte red   = png_ptr->gamma_to_1[*(sp++)];
-                  png_byte green = png_ptr->gamma_to_1[*(sp++)];
-                  png_byte blue  = png_ptr->gamma_to_1[*(sp++)];
-                  if (red != green || red != blue)
-                    rgb_error |= 1;
-                  *(dp++) =  png_ptr->gamma_from_1
-                             [(rc*red + gc*green + bc*blue)>>15];
-                  *(dp++) = *(sp++);  /* alpha */
-               }
-            }
-            else
-#endif
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_byte red   = *(sp++);
-                  png_byte green = *(sp++);
-                  png_byte blue  = *(sp++);
-                  if (red != green || red != blue)
-                    rgb_error |= 1;
-                  *(dp++) =  (png_byte)((rc*red + gc*green + bc*blue)>>15);
-                  *(dp++) = *(sp++);  /* alpha */
-               }
-            }
-         }
-         else /* RGBA bit_depth == 16 */
-         {
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
-            if (png_ptr->gamma_16_to_1 != NULL &&
-                png_ptr->gamma_16_from_1 != NULL)
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 red, green, blue, w;
-
-                  red   = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-                  green = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-                  blue  = (png_uint_16)(((*(sp))<<8) | *(sp+1)); sp+=2;
-
-                  if (red == green && red == blue)
-                    w = red;
-                  else
-                  {
-                     png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff) >>
-                                  png_ptr->gamma_shift][red>>8];
-                     png_uint_16 green_1 = png_ptr->gamma_16_to_1[(green&0xff) >>
-                                  png_ptr->gamma_shift][green>>8];
-                     png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff) >>
-                                  png_ptr->gamma_shift][blue>>8];
-                     png_uint_16 gray16  = (png_uint_16)((rc * red_1
-                                  + gc * green_1 + bc * blue_1)>>15);
-                     w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
-                         png_ptr->gamma_shift][gray16 >> 8];
-                     rgb_error |= 1;
-                  }
-
-                  *(dp++) = (png_byte)((w>>8) & 0xff);
-                  *(dp++) = (png_byte)(w & 0xff);
-                  *(dp++) = *(sp++);  /* alpha */
+               }
+
+               else
+               {
+                  png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff)
+                      >> png_ptr->gamma_shift][red>>8];
+                  png_uint_16 green_1 =
+                      png_ptr->gamma_16_to_1[(green&0xff) >>
+                      png_ptr->gamma_shift][green>>8];
+                  png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff)
+                      >> png_ptr->gamma_shift][blue>>8];
+                  png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
+                      + bc*blue_1 + 16384)>>15);
+                  w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
+                      png_ptr->gamma_shift][gray16 >> 8];
+                  rgb_error |= 1;
+               }
+
+               *(dp++) = (png_byte)((w>>8) & 0xff);
+               *(dp++) = (png_byte)(w & 0xff);
+
+               if (have_alpha)
+               {
                   *(dp++) = *(sp++);
-               }
-            }
-            else
-#endif
-            {
-               png_bytep sp = row;
-               png_bytep dp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 red, green, blue, gray16;
-                  red   = (png_uint_16)((*(sp)<<8) | *(sp+1)); sp+=2;
-                  green = (png_uint_16)((*(sp)<<8) | *(sp+1)); sp+=2;
-                  blue  = (png_uint_16)((*(sp)<<8) | *(sp+1)); sp+=2;
-                  if (red != green || red != blue)
-                    rgb_error |= 1;
-                  gray16  = (png_uint_16)((rc*red + gc*green + bc*blue)>>15);
-                  *(dp++) = (png_byte)((gray16>>8) & 0xff);
-                  *(dp++) = (png_byte)(gray16 & 0xff);
-                  *(dp++) = *(sp++);  /* alpha */
                   *(dp++) = *(sp++);
                }
             }
          }
-      }
-   row_info->channels -= (png_byte)2;
-      row_info->color_type &= ~PNG_COLOR_MASK_COLOR;
+         else
+#endif
+         {
+            png_bytep sp = row;
+            png_bytep dp = row;
+            png_uint_32 i;
+
+            for (i = 0; i < row_width; i++)
+            {
+               png_uint_16 red, green, blue, gray16;
+
+               red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
+               green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
+               blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
+
+               if (red != green || red != blue)
+                  rgb_error |= 1;
+
+               /* From 1.5.5 in the 16 bit case do the accurate conversion even
+                * in the 'fast' case - this is because this is where the code
+                * ends up when handling linear 16 bit data.
+                */
+               gray16  = (png_uint_16)((rc*red + gc*green + bc*blue + 16384) >>
+                  15);
+               *(dp++) = (png_byte)((gray16>>8) & 0xff);
+               *(dp++) = (png_byte)(gray16 & 0xff);
+
+               if (have_alpha)
+               {
+                  *(dp++) = *(sp++);
+                  *(dp++) = *(sp++);
+               }
+            }
+         }
+      }
+
+      row_info->channels = (png_byte)(row_info->channels - 2);
+      row_info->color_type = (png_byte)(row_info->color_type &
+          ~PNG_COLOR_MASK_COLOR);
       row_info->pixel_depth = (png_byte)(row_info->channels *
-         row_info->bit_depth);
-      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,row_width);
+          row_info->bit_depth);
+      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
    }
    return rgb_error;
 }
 #endif
-
+#endif /* PNG_READ_TRANSFORMS_SUPPORTED */
+
+#ifdef PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED
 /* Build a grayscale palette.  Palette is assumed to be 1 << bit_depth
  * large of png_color.  This lets grayscale images be treated as
  * paletted.  Most useful for gamma correction and simplification
- * of code.
+ * of code.  This API is not used internally.
  */
 void PNGAPI
 png_build_grayscale_palette(int bit_depth, png_colorp palette)
@@ -2362,7 +3432,8 @@
    int i;
    int v;
 
-   png_debug(1, "in png_do_build_grayscale_palette\n");
+   png_debug(1, "in png_do_build_grayscale_palette");
+
    if (palette == NULL)
       return;
 
@@ -2372,18 +3443,22 @@
          num_palette = 2;
          color_inc = 0xff;
          break;
+
       case 2:
          num_palette = 4;
          color_inc = 0x55;
          break;
+
       case 4:
          num_palette = 16;
          color_inc = 0x11;
          break;
+
       case 8:
          num_palette = 256;
          color_inc = 1;
          break;
+
       default:
          num_palette = 0;
          color_inc = 0;
@@ -2397,217 +3472,37 @@
       palette[i].blue = (png_byte)v;
    }
 }
-
-/* This function is currently unused.  Do we really need it? */
-#if defined(PNG_READ_DITHER_SUPPORTED) && defined(PNG_CORRECT_PALETTE_SUPPORTED)
-void /* PRIVATE */
-png_correct_palette(png_structp png_ptr, png_colorp palette,
-                    int num_palette)
-{
-   png_debug(1, "in png_correct_palette\n");
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
-    defined(PNG_READ_GAMMA_SUPPORTED) && defined(PNG_FLOATING_POINT_SUPPORTED)
-   if (png_ptr->transformations & (PNG_GAMMA | PNG_BACKGROUND))
-   {
-      png_color back, back_1;
-
-      if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
-      {
-         back.red = png_ptr->gamma_table[png_ptr->background.red];
-         back.green = png_ptr->gamma_table[png_ptr->background.green];
-         back.blue = png_ptr->gamma_table[png_ptr->background.blue];
-
-         back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
-         back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
-         back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
-      }
-      else
-      {
-         double g;
-
-         g = 1.0 / (png_ptr->background_gamma * png_ptr->screen_gamma);
-
-         if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_SCREEN ||
-             fabs(g - 1.0) < PNG_GAMMA_THRESHOLD)
-         {
-            back.red = png_ptr->background.red;
-            back.green = png_ptr->background.green;
-            back.blue = png_ptr->background.blue;
-         }
-         else
-         {
-            back.red =
-               (png_byte)(pow((double)png_ptr->background.red/255, g) *
-                255.0 + 0.5);
-            back.green =
-               (png_byte)(pow((double)png_ptr->background.green/255, g) *
-                255.0 + 0.5);
-            back.blue =
-               (png_byte)(pow((double)png_ptr->background.blue/255, g) *
-                255.0 + 0.5);
-         }
-
-         g = 1.0 / png_ptr->background_gamma;
-
-         back_1.red =
-            (png_byte)(pow((double)png_ptr->background.red/255, g) *
-             255.0 + 0.5);
-         back_1.green =
-            (png_byte)(pow((double)png_ptr->background.green/255, g) *
-             255.0 + 0.5);
-         back_1.blue =
-            (png_byte)(pow((double)png_ptr->background.blue/255, g) *
-             255.0 + 0.5);
-      }
-
-      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-      {
-         png_uint_32 i;
-
-         for (i = 0; i < (png_uint_32)num_palette; i++)
-         {
-            if (i < png_ptr->num_trans && png_ptr->trans[i] == 0)
-            {
-               palette[i] = back;
-            }
-            else if (i < png_ptr->num_trans && png_ptr->trans[i] != 0xff)
-            {
-               png_byte v, w;
-
-               v = png_ptr->gamma_to_1[png_ptr->palette[i].red];
-               png_composite(w, v, png_ptr->trans[i], back_1.red);
-               palette[i].red = png_ptr->gamma_from_1[w];
-
-               v = png_ptr->gamma_to_1[png_ptr->palette[i].green];
-               png_composite(w, v, png_ptr->trans[i], back_1.green);
-               palette[i].green = png_ptr->gamma_from_1[w];
-
-               v = png_ptr->gamma_to_1[png_ptr->palette[i].blue];
-               png_composite(w, v, png_ptr->trans[i], back_1.blue);
-               palette[i].blue = png_ptr->gamma_from_1[w];
-            }
-            else
-            {
-               palette[i].red = png_ptr->gamma_table[palette[i].red];
-               palette[i].green = png_ptr->gamma_table[palette[i].green];
-               palette[i].blue = png_ptr->gamma_table[palette[i].blue];
-            }
-         }
-      }
-      else
-      {
-         int i;
-
-         for (i = 0; i < num_palette; i++)
-         {
-            if (palette[i].red == (png_byte)png_ptr->trans_values.gray)
-            {
-               palette[i] = back;
-            }
-            else
-            {
-               palette[i].red = png_ptr->gamma_table[palette[i].red];
-               palette[i].green = png_ptr->gamma_table[palette[i].green];
-               palette[i].blue = png_ptr->gamma_table[palette[i].blue];
-            }
-         }
-      }
-   }
-   else
-#endif
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-   if (png_ptr->transformations & PNG_GAMMA)
-   {
-      int i;
-
-      for (i = 0; i < num_palette; i++)
-      {
-         palette[i].red = png_ptr->gamma_table[palette[i].red];
-         palette[i].green = png_ptr->gamma_table[palette[i].green];
-         palette[i].blue = png_ptr->gamma_table[palette[i].blue];
-      }
-   }
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-   else
-#endif
-#endif
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
-   if (png_ptr->transformations & PNG_BACKGROUND)
-   {
-      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-      {
-         png_color back;
-
-         back.red   = (png_byte)png_ptr->background.red;
-         back.green = (png_byte)png_ptr->background.green;
-         back.blue  = (png_byte)png_ptr->background.blue;
-
-         for (i = 0; i < (int)png_ptr->num_trans; i++)
-         {
-            if (png_ptr->trans[i] == 0)
-            {
-               palette[i].red = back.red;
-               palette[i].green = back.green;
-               palette[i].blue = back.blue;
-            }
-            else if (png_ptr->trans[i] != 0xff)
-            {
-               png_composite(palette[i].red, png_ptr->palette[i].red,
-                  png_ptr->trans[i], back.red);
-               png_composite(palette[i].green, png_ptr->palette[i].green,
-                  png_ptr->trans[i], back.green);
-               png_composite(palette[i].blue, png_ptr->palette[i].blue,
-                  png_ptr->trans[i], back.blue);
-            }
-         }
-      }
-      else /* assume grayscale palette (what else could it be?) */
-      {
-         int i;
-
-         for (i = 0; i < num_palette; i++)
-         {
-            if (i == (png_byte)png_ptr->trans_values.gray)
-            {
-               palette[i].red = (png_byte)png_ptr->background.red;
-               palette[i].green = (png_byte)png_ptr->background.green;
-               palette[i].blue = (png_byte)png_ptr->background.blue;
-            }
-         }
-      }
-   }
-#endif
-}
-#endif
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED)
+#endif
+
+
+#ifdef PNG_READ_TRANSFORMS_SUPPORTED
+#if (defined PNG_READ_BACKGROUND_SUPPORTED) ||\
+   (defined PNG_READ_ALPHA_MODE_SUPPORTED)
 /* Replace any alpha or transparency with the supplied background color.
  * "background" is already in the screen gamma, while "background_1" is
  * at a gamma of 1.0.  Paletted files have already been taken care of.
  */
 void /* PRIVATE */
-png_do_background(png_row_infop row_info, png_bytep row,
-                  png_color_16p trans_values, png_color_16p background
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-   , png_color_16p background_1,
-   png_bytep gamma_table, png_bytep gamma_from_1, png_bytep gamma_to_1,
-   png_uint_16pp gamma_16, png_uint_16pp gamma_16_from_1,
-   png_uint_16pp gamma_16_to_1, int gamma_shift
-#endif
-   )
+png_do_compose(png_row_infop row_info, png_bytep row, png_structp png_ptr)
 {
-   png_bytep sp, dp;
+#ifdef PNG_READ_GAMMA_SUPPORTED
+   png_const_bytep gamma_table = png_ptr->gamma_table;
+   png_const_bytep gamma_from_1 = png_ptr->gamma_from_1;
+   png_const_bytep gamma_to_1 = png_ptr->gamma_to_1;
+   png_const_uint_16pp gamma_16 = png_ptr->gamma_16_table;
+   png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
+   png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
+   int gamma_shift = png_ptr->gamma_shift;
+#endif
+
+   png_bytep sp;
    png_uint_32 i;
-   png_uint_32 row_width=row_info->width;
+   png_uint_32 row_width = row_info->width;
+   int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
    int shift;
 
-   png_debug(1, "in png_do_background\n");
-   if (background != NULL &&
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL &&
-#endif
-      (!(row_info->color_type & PNG_COLOR_MASK_ALPHA) ||
-      (row_info->color_type != PNG_COLOR_TYPE_PALETTE && trans_values)))
+   png_debug(1, "in png_do_compose");
+
    {
       switch (row_info->color_type)
       {
@@ -2622,24 +3517,27 @@
                   for (i = 0; i < row_width; i++)
                   {
                      if ((png_uint_16)((*sp >> shift) & 0x01)
-                        == trans_values->gray)
+                        == png_ptr->trans_color.gray)
                      {
                         *sp &= (png_byte)((0x7f7f >> (7 - shift)) & 0xff);
-                        *sp |= (png_byte)(background->gray << shift);
+                        *sp |= (png_byte)(png_ptr->background.gray << shift);
                      }
+
                      if (!shift)
                      {
                         shift = 7;
                         sp++;
                      }
+
                      else
                         shift--;
                   }
                   break;
                }
+
                case 2:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
@@ -2647,11 +3545,12 @@
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x03)
-                            == trans_values->gray)
+                            == png_ptr->trans_color.gray)
                         {
                            *sp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
-                           *sp |= (png_byte)(background->gray << shift);
+                           *sp |= (png_byte)(png_ptr->background.gray << shift);
                         }
+
                         else
                         {
                            png_byte p = (png_byte)((*sp >> shift) & 0x03);
@@ -2660,15 +3559,18 @@
                            *sp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
                            *sp |= (png_byte)(g << shift);
                         }
+
                         if (!shift)
                         {
                            shift = 6;
                            sp++;
                         }
+
                         else
                            shift -= 2;
                      }
                   }
+
                   else
 #endif
                   {
@@ -2677,25 +3579,28 @@
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x03)
-                            == trans_values->gray)
+                            == png_ptr->trans_color.gray)
                         {
                            *sp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
-                           *sp |= (png_byte)(background->gray << shift);
+                           *sp |= (png_byte)(png_ptr->background.gray << shift);
                         }
+
                         if (!shift)
                         {
                            shift = 6;
                            sp++;
                         }
+
                         else
                            shift -= 2;
                      }
                   }
                   break;
                }
+
                case 4:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
@@ -2703,28 +3608,32 @@
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x0f)
-                            == trans_values->gray)
+                            == png_ptr->trans_color.gray)
                         {
                            *sp &= (png_byte)((0xf0f >> (4 - shift)) & 0xff);
-                           *sp |= (png_byte)(background->gray << shift);
+                           *sp |= (png_byte)(png_ptr->background.gray << shift);
                         }
+
                         else
                         {
                            png_byte p = (png_byte)((*sp >> shift) & 0x0f);
                            png_byte g = (png_byte)((gamma_table[p |
-                             (p << 4)] >> 4) & 0x0f);
+                               (p << 4)] >> 4) & 0x0f);
                            *sp &= (png_byte)((0xf0f >> (4 - shift)) & 0xff);
                            *sp |= (png_byte)(g << shift);
                         }
+
                         if (!shift)
                         {
                            shift = 4;
                            sp++;
                         }
+
                         else
                            shift -= 4;
                      }
                   }
+
                   else
 #endif
                   {
@@ -2733,38 +3642,38 @@
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x0f)
-                            == trans_values->gray)
+                            == png_ptr->trans_color.gray)
                         {
                            *sp &= (png_byte)((0xf0f >> (4 - shift)) & 0xff);
-                           *sp |= (png_byte)(background->gray << shift);
+                           *sp |= (png_byte)(png_ptr->background.gray << shift);
                         }
+
                         if (!shift)
                         {
                            shift = 4;
                            sp++;
                         }
+
                         else
                            shift -= 4;
                      }
                   }
                   break;
                }
+
                case 8:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp++)
                      {
-                        if (*sp == trans_values->gray)
-                        {
-                           *sp = (png_byte)background->gray;
-                        }
+                        if (*sp == png_ptr->trans_color.gray)
+                           *sp = (png_byte)png_ptr->background.gray;
+
                         else
-                        {
                            *sp = gamma_table[*sp];
-                        }
                      }
                   }
                   else
@@ -2773,17 +3682,16 @@
                      sp = row;
                      for (i = 0; i < row_width; i++, sp++)
                      {
-                        if (*sp == trans_values->gray)
-                        {
-                           *sp = (png_byte)background->gray;
-                        }
+                        if (*sp == png_ptr->trans_color.gray)
+                           *sp = (png_byte)png_ptr->background.gray;
                      }
                   }
                   break;
                }
+
                case 16:
                {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_16 != NULL)
                   {
                      sp = row;
@@ -2792,12 +3700,14 @@
                         png_uint_16 v;
 
                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-                        if (v == trans_values->gray)
+
+                        if (v == png_ptr->trans_color.gray)
                         {
-                           /* background is already in screen gamma */
-                           *sp = (png_byte)((background->gray >> 8) & 0xff);
-                           *(sp + 1) = (png_byte)(background->gray & 0xff);
+                           /* Background is already in screen gamma */
+                           *sp = (png_byte)((png_ptr->background.gray >> 8) & 0xff);
+                           *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                         }
+
                         else
                         {
                            v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
@@ -2815,36 +3725,42 @@
                         png_uint_16 v;
 
                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-                        if (v == trans_values->gray)
+
+                        if (v == png_ptr->trans_color.gray)
                         {
-                           *sp = (png_byte)((background->gray >> 8) & 0xff);
-                           *(sp + 1) = (png_byte)(background->gray & 0xff);
+                           *sp = (png_byte)((png_ptr->background.gray >> 8) & 0xff);
+                           *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                         }
                      }
                   }
                   break;
                }
+
+               default:
+                  break;
             }
             break;
          }
+
          case PNG_COLOR_TYPE_RGB:
          {
             if (row_info->bit_depth == 8)
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_table != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 3)
                   {
-                     if (*sp == trans_values->red &&
-                        *(sp + 1) == trans_values->green &&
-                        *(sp + 2) == trans_values->blue)
+                     if (*sp == png_ptr->trans_color.red &&
+                         *(sp + 1) == png_ptr->trans_color.green &&
+                         *(sp + 2) == png_ptr->trans_color.blue)
                      {
-                        *sp = (png_byte)background->red;
-                        *(sp + 1) = (png_byte)background->green;
-                        *(sp + 2) = (png_byte)background->blue;
+                        *sp = (png_byte)png_ptr->background.red;
+                        *(sp + 1) = (png_byte)png_ptr->background.green;
+                        *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
+
                      else
                      {
                         *sp = gamma_table[*sp];
@@ -2859,108 +3775,125 @@
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 3)
                   {
-                     if (*sp == trans_values->red &&
-                        *(sp + 1) == trans_values->green &&
-                        *(sp + 2) == trans_values->blue)
+                     if (*sp == png_ptr->trans_color.red &&
+                         *(sp + 1) == png_ptr->trans_color.green &&
+                         *(sp + 2) == png_ptr->trans_color.blue)
                      {
-                        *sp = (png_byte)background->red;
-                        *(sp + 1) = (png_byte)background->green;
-                        *(sp + 2) = (png_byte)background->blue;
+                        *sp = (png_byte)png_ptr->background.red;
+                        *(sp + 1) = (png_byte)png_ptr->background.green;
+                        *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
                   }
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 6)
                   {
                      png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-                     png_uint_16 g = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
-                     png_uint_16 b = (png_uint_16)(((*(sp+4)) << 8) + *(sp+5));
-                     if (r == trans_values->red && g == trans_values->green &&
-                        b == trans_values->blue)
+
+                     png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
+                         + *(sp + 3));
+
+                     png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
+                         + *(sp + 5));
+
+                     if (r == png_ptr->trans_color.red &&
+                         g == png_ptr->trans_color.green &&
+                         b == png_ptr->trans_color.blue)
                      {
-                        /* background is already in screen gamma */
-                        *sp = (png_byte)((background->red >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(background->red & 0xff);
-                        *(sp + 2) = (png_byte)((background->green >> 8) & 0xff);
-                        *(sp + 3) = (png_byte)(background->green & 0xff);
-                        *(sp + 4) = (png_byte)((background->blue >> 8) & 0xff);
-                        *(sp + 5) = (png_byte)(background->blue & 0xff);
+                        /* Background is already in screen gamma */
+                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
+                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(png_ptr->background.green & 0xff);
+                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
+
                      else
                      {
                         png_uint_16 v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                         *sp = (png_byte)((v >> 8) & 0xff);
                         *(sp + 1) = (png_byte)(v & 0xff);
+
                         v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 3) = (png_byte)(v & 0xff);
+
                         v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                         *(sp + 5) = (png_byte)(v & 0xff);
                      }
                   }
                }
+
                else
 #endif
                {
                   sp = row;
                   for (i = 0; i < row_width; i++, sp += 6)
                   {
-                     png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp+1));
-                     png_uint_16 g = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
-                     png_uint_16 b = (png_uint_16)(((*(sp+4)) << 8) + *(sp+5));
-
-                     if (r == trans_values->red && g == trans_values->green &&
-                        b == trans_values->blue)
+                     png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
+
+                     png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
+                         + *(sp + 3));
+
+                     png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
+                         + *(sp + 5));
+
+                     if (r == png_ptr->trans_color.red &&
+                         g == png_ptr->trans_color.green &&
+                         b == png_ptr->trans_color.blue)
                      {
-                        *sp = (png_byte)((background->red >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(background->red & 0xff);
-                        *(sp + 2) = (png_byte)((background->green >> 8) & 0xff);
-                        *(sp + 3) = (png_byte)(background->green & 0xff);
-                        *(sp + 4) = (png_byte)((background->blue >> 8) & 0xff);
-                        *(sp + 5) = (png_byte)(background->blue & 0xff);
+                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
+                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(png_ptr->background.green & 0xff);
+                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
                   }
                }
             }
             break;
          }
+
          case PNG_COLOR_TYPE_GRAY_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                    gamma_table != NULL)
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 2, dp++)
+                  for (i = 0; i < row_width; i++, sp += 2)
                   {
                      png_uint_16 a = *(sp + 1);
 
                      if (a == 0xff)
-                     {
-                        *dp = gamma_table[*sp];
-                     }
+                        *sp = gamma_table[*sp];
+
                      else if (a == 0)
                      {
-                        /* background is already in screen gamma */
-                        *dp = (png_byte)background->gray;
+                        /* Background is already in screen gamma */
+                        *sp = (png_byte)png_ptr->background.gray;
                      }
+
                      else
                      {
                         png_byte v, w;
 
                         v = gamma_to_1[*sp];
-                        png_composite(w, v, a, background_1->gray);
-                        *dp = gamma_from_1[w];
+                        png_composite(w, v, a, png_ptr->background_1.gray);
+                        if (!optimize)
+                           w = gamma_from_1[w];
+                        *sp = w;
                      }
                   }
                }
@@ -2968,151 +3901,137 @@
 #endif
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 2, dp++)
+                  for (i = 0; i < row_width; i++, sp += 2)
                   {
                      png_byte a = *(sp + 1);
 
-                     if (a == 0xff)
-                     {
-                        *dp = *sp;
-                     }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-                     else if (a == 0)
-                     {
-                        *dp = (png_byte)background->gray;
-                     }
-                     else
-                     {
-                        png_composite(*dp, *sp, a, background_1->gray);
-                     }
-#else
-                     *dp = (png_byte)background->gray;
-#endif
+                     if (a == 0)
+                        *sp = (png_byte)png_ptr->background.gray;
+
+                     else if (a < 0xff)
+                        png_composite(*sp, *sp, a, png_ptr->background_1.gray);
                   }
                }
             }
             else /* if (png_ptr->bit_depth == 16) */
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                    gamma_16_to_1 != NULL)
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 4, dp += 2)
+                  for (i = 0; i < row_width; i++, sp += 4)
                   {
-                     png_uint_16 a = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
+                     png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
+                         + *(sp + 3));
 
                      if (a == (png_uint_16)0xffff)
                      {
                         png_uint_16 v;
 
                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
-                        *dp = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(v & 0xff);
+                        *sp = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(v & 0xff);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+
                      else if (a == 0)
-#else
-                     else
-#endif
                      {
-                        /* background is already in screen gamma */
-                        *dp = (png_byte)((background->gray >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(background->gray & 0xff);
+                        /* Background is already in screen gamma */
+                        *sp = (png_byte)((png_ptr->background.gray >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+
                      else
                      {
                         png_uint_16 g, v, w;
 
                         g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
-                        png_composite_16(v, g, a, background_1->gray);
-                        w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
-                        *dp = (png_byte)((w >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(w & 0xff);
+                        png_composite_16(v, g, a, png_ptr->background_1.gray);
+                        if (optimize)
+                           w = v;
+                        else
+                           w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
+                        *sp = (png_byte)((w >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(w & 0xff);
                      }
-#endif
                   }
                }
                else
 #endif
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 4, dp += 2)
+                  for (i = 0; i < row_width; i++, sp += 4)
                   {
-                     png_uint_16 a = (png_uint_16)(((*(sp+2)) << 8) + *(sp+3));
-                     if (a == (png_uint_16)0xffff)
+                     png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
+                         + *(sp + 3));
+
+                     if (a == 0)
                      {
-                        png_memcpy(dp, sp, 2);
+                        *sp = (png_byte)((png_ptr->background.gray >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                      }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-                     else if (a == 0)
-#else
-                     else
-#endif
-                     {
-                        *dp = (png_byte)((background->gray >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(background->gray & 0xff);
-                     }
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-                     else
+
+                     else if (a < 0xffff)
                      {
                         png_uint_16 g, v;
 
                         g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-                        png_composite_16(v, g, a, background_1->gray);
-                        *dp = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(v & 0xff);
+                        png_composite_16(v, g, a, png_ptr->background_1.gray);
+                        *sp = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(v & 0xff);
                      }
-#endif
                   }
                }
             }
             break;
          }
+
          case PNG_COLOR_TYPE_RGB_ALPHA:
          {
             if (row_info->bit_depth == 8)
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                    gamma_table != NULL)
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 4, dp += 3)
+                  for (i = 0; i < row_width; i++, sp += 4)
                   {
                      png_byte a = *(sp + 3);
 
                      if (a == 0xff)
                      {
-                        *dp = gamma_table[*sp];
-                        *(dp + 1) = gamma_table[*(sp + 1)];
-                        *(dp + 2) = gamma_table[*(sp + 2)];
+                        *sp = gamma_table[*sp];
+                        *(sp + 1) = gamma_table[*(sp + 1)];
+                        *(sp + 2) = gamma_table[*(sp + 2)];
                      }
+
                      else if (a == 0)
                      {
-                        /* background is already in screen gamma */
-                        *dp = (png_byte)background->red;
-                        *(dp + 1) = (png_byte)background->green;
-                        *(dp + 2) = (png_byte)background->blue;
+                        /* Background is already in screen gamma */
+                        *sp = (png_byte)png_ptr->background.red;
+                        *(sp + 1) = (png_byte)png_ptr->background.green;
+                        *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
+
                      else
                      {
                         png_byte v, w;
 
                         v = gamma_to_1[*sp];
-                        png_composite(w, v, a, background_1->red);
-                        *dp = gamma_from_1[w];
+                        png_composite(w, v, a, png_ptr->background_1.red);
+                        if (!optimize) w = gamma_from_1[w];
+                        *sp = w;
+
                         v = gamma_to_1[*(sp + 1)];
-                        png_composite(w, v, a, background_1->green);
-                        *(dp + 1) = gamma_from_1[w];
+                        png_composite(w, v, a, png_ptr->background_1.green);
+                        if (!optimize) w = gamma_from_1[w];
+                        *(sp + 1) = w;
+
                         v = gamma_to_1[*(sp + 2)];
-                        png_composite(w, v, a, background_1->blue);
-                        *(dp + 2) = gamma_from_1[w];
+                        png_composite(w, v, a, png_ptr->background_1.blue);
+                        if (!optimize) w = gamma_from_1[w];
+                        *(sp + 2) = w;
                      }
                   }
                }
@@ -3120,115 +4039,120 @@
 #endif
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 4, dp += 3)
+                  for (i = 0; i < row_width; i++, sp += 4)
                   {
                      png_byte a = *(sp + 3);
 
-                     if (a == 0xff)
+                     if (a == 0)
                      {
-                        *dp = *sp;
-                        *(dp + 1) = *(sp + 1);
-                        *(dp + 2) = *(sp + 2);
+                        *sp = (png_byte)png_ptr->background.red;
+                        *(sp + 1) = (png_byte)png_ptr->background.green;
+                        *(sp + 2) = (png_byte)png_ptr->background.blue;
                      }
-                     else if (a == 0)
+
+                     else if (a < 0xff)
                      {
-                        *dp = (png_byte)background->red;
-                        *(dp + 1) = (png_byte)background->green;
-                        *(dp + 2) = (png_byte)background->blue;
-                     }
-                     else
-                     {
-                        png_composite(*dp, *sp, a, background->red);
-                        png_composite(*(dp + 1), *(sp + 1), a,
-                           background->green);
-                        png_composite(*(dp + 2), *(sp + 2), a,
-                           background->blue);
+                        png_composite(*sp, *sp, a, png_ptr->background.red);
+
+                        png_composite(*(sp + 1), *(sp + 1), a,
+                            png_ptr->background.green);
+
+                        png_composite(*(sp + 2), *(sp + 2), a,
+                            png_ptr->background.blue);
                      }
                   }
                }
             }
             else /* if (row_info->bit_depth == 16) */
             {
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                    gamma_16_to_1 != NULL)
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 8, dp += 6)
+                  for (i = 0; i < row_width; i++, sp += 8)
                   {
                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                          << 8) + (png_uint_16)(*(sp + 7)));
+
                      if (a == (png_uint_16)0xffff)
                      {
                         png_uint_16 v;
 
                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
-                        *dp = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(v & 0xff);
+                        *sp = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(v & 0xff);
+
                         v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
-                        *(dp + 2) = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 3) = (png_byte)(v & 0xff);
+                        *(sp + 2) = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(v & 0xff);
+
                         v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
-                        *(dp + 4) = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 5) = (png_byte)(v & 0xff);
+                        *(sp + 4) = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(v & 0xff);
                      }
+
                      else if (a == 0)
                      {
-                        /* background is already in screen gamma */
-                        *dp = (png_byte)((background->red >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(background->red & 0xff);
-                        *(dp + 2) = (png_byte)((background->green >> 8) & 0xff);
-                        *(dp + 3) = (png_byte)(background->green & 0xff);
-                        *(dp + 4) = (png_byte)((background->blue >> 8) & 0xff);
-                        *(dp + 5) = (png_byte)(background->blue & 0xff);
+                        /* Background is already in screen gamma */
+                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
+                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(png_ptr->background.green & 0xff);
+                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
+
                      else
                      {
-                        png_uint_16 v, w, x;
+                        png_uint_16 v, w;
 
                         v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
-                        png_composite_16(w, v, a, background_1->red);
-                        x = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
-                        *dp = (png_byte)((x >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(x & 0xff);
+                        png_composite_16(w, v, a, png_ptr->background_1.red);
+                        if (!optimize)
+                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
+                        *sp = (png_byte)((w >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(w & 0xff);
+
                         v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
-                        png_composite_16(w, v, a, background_1->green);
-                        x = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
-                        *(dp + 2) = (png_byte)((x >> 8) & 0xff);
-                        *(dp + 3) = (png_byte)(x & 0xff);
+                        png_composite_16(w, v, a, png_ptr->background_1.green);
+                        if (!optimize)
+                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
+
+                        *(sp + 2) = (png_byte)((w >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(w & 0xff);
+
                         v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
-                        png_composite_16(w, v, a, background_1->blue);
-                        x = gamma_16_from_1[(w & 0xff) >> gamma_shift][w >> 8];
-                        *(dp + 4) = (png_byte)((x >> 8) & 0xff);
-                        *(dp + 5) = (png_byte)(x & 0xff);
+                        png_composite_16(w, v, a, png_ptr->background_1.blue);
+                        if (!optimize)
+                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
+
+                        *(sp + 4) = (png_byte)((w >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(w & 0xff);
                      }
                   }
                }
+
                else
 #endif
                {
                   sp = row;
-                  dp = row;
-                  for (i = 0; i < row_width; i++, sp += 8, dp += 6)
+                  for (i = 0; i < row_width; i++, sp += 8)
                   {
                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
-                        << 8) + (png_uint_16)(*(sp + 7)));
-                     if (a == (png_uint_16)0xffff)
+                         << 8) + (png_uint_16)(*(sp + 7)));
+
+                     if (a == 0)
                      {
-                        png_memcpy(dp, sp, 6);
+                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
+                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(png_ptr->background.green & 0xff);
+                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                      }
-                     else if (a == 0)
-                     {
-                        *dp = (png_byte)((background->red >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(background->red & 0xff);
-                        *(dp + 2) = (png_byte)((background->green >> 8) & 0xff);
-                        *(dp + 3) = (png_byte)(background->green & 0xff);
-                        *(dp + 4) = (png_byte)((background->blue >> 8) & 0xff);
-                        *(dp + 5) = (png_byte)(background->blue & 0xff);
-                     }
-                     else
+
+                     else if (a < 0xffff)
                      {
                         png_uint_16 v;
 
@@ -3238,36 +4162,32 @@
                         png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                             + *(sp + 5));
 
-                        png_composite_16(v, r, a, background->red);
-                        *dp = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 1) = (png_byte)(v & 0xff);
-                        png_composite_16(v, g, a, background->green);
-                        *(dp + 2) = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 3) = (png_byte)(v & 0xff);
-                        png_composite_16(v, b, a, background->blue);
-                        *(dp + 4) = (png_byte)((v >> 8) & 0xff);
-                        *(dp + 5) = (png_byte)(v & 0xff);
+                        png_composite_16(v, r, a, png_ptr->background.red);
+                        *sp = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 1) = (png_byte)(v & 0xff);
+
+                        png_composite_16(v, g, a, png_ptr->background.green);
+                        *(sp + 2) = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 3) = (png_byte)(v & 0xff);
+
+                        png_composite_16(v, b, a, png_ptr->background.blue);
+                        *(sp + 4) = (png_byte)((v >> 8) & 0xff);
+                        *(sp + 5) = (png_byte)(v & 0xff);
                      }
                   }
                }
             }
             break;
          }
-      }
-
-      if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
-      {
-         row_info->color_type &= ~PNG_COLOR_MASK_ALPHA;
-         row_info->channels--;
-         row_info->pixel_depth = (png_byte)(row_info->channels *
-            row_info->bit_depth);
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,row_width);
+
+         default:
+            break;
       }
    }
 }
-#endif
-
-#if defined(PNG_READ_GAMMA_SUPPORTED)
+#endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_READ_ALPHA_MODE_SUPPORTED */
+
+#ifdef PNG_READ_GAMMA_SUPPORTED
 /* Gamma correct the image, avoiding the alpha channel.  Make sure
  * you do this after you deal with the transparency issue on grayscale
  * or RGB images. If your bit depth is 8, use gamma_table, if it
@@ -3275,21 +4195,20 @@
  * build_gamma_table().
  */
 void /* PRIVATE */
-png_do_gamma(png_row_infop row_info, png_bytep row,
-             png_bytep gamma_table, png_uint_16pp gamma_16_table,
-             int gamma_shift)
+png_do_gamma(png_row_infop row_info, png_bytep row, png_structp png_ptr)
 {
+   png_const_bytep gamma_table = png_ptr->gamma_table;
+   png_const_uint_16pp gamma_16_table = png_ptr->gamma_16_table;
+   int gamma_shift = png_ptr->gamma_shift;
+
    png_bytep sp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
-   png_debug(1, "in png_do_gamma\n");
-   if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL &&
-#endif
-       ((row_info->bit_depth <= 8 && gamma_table != NULL) ||
-        (row_info->bit_depth == 16 && gamma_16_table != NULL)))
+   png_debug(1, "in png_do_gamma");
+
+   if (((row_info->bit_depth <= 8 && gamma_table != NULL) ||
+       (row_info->bit_depth == 16 && gamma_16_table != NULL)))
    {
       switch (row_info->color_type)
       {
@@ -3308,6 +4227,7 @@
                   sp++;
                }
             }
+
             else /* if (row_info->bit_depth == 16) */
             {
                sp = row;
@@ -3319,10 +4239,12 @@
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
+
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
+
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
@@ -3331,6 +4253,7 @@
             }
             break;
          }
+
          case PNG_COLOR_TYPE_RGB_ALPHA:
          {
             if (row_info->bit_depth == 8)
@@ -3340,13 +4263,17 @@
                {
                   *sp = gamma_table[*sp];
                   sp++;
+
                   *sp = gamma_table[*sp];
                   sp++;
+
                   *sp = gamma_table[*sp];
                   sp++;
+
                   sp++;
                }
             }
+
             else /* if (row_info->bit_depth == 16) */
             {
                sp = row;
@@ -3356,10 +4283,12 @@
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
+
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
                   sp += 2;
+
                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                   *sp = (png_byte)((v >> 8) & 0xff);
                   *(sp + 1) = (png_byte)(v & 0xff);
@@ -3368,6 +4297,7 @@
             }
             break;
          }
+
          case PNG_COLOR_TYPE_GRAY_ALPHA:
          {
             if (row_info->bit_depth == 8)
@@ -3379,6 +4309,7 @@
                   sp += 2;
                }
             }
+
             else /* if (row_info->bit_depth == 16) */
             {
                sp = row;
@@ -3392,6 +4323,7 @@
             }
             break;
          }
+
          case PNG_COLOR_TYPE_GRAY:
          {
             if (row_info->bit_depth == 2)
@@ -3405,13 +4337,14 @@
                   int d = *sp & 0x03;
 
                   *sp = (png_byte)(
-                        ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
-                        ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
-                        ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
-                        ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
+                      ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
+                      ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
+                      ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
+                      ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
                   sp++;
                }
             }
+
             if (row_info->bit_depth == 4)
             {
                sp = row;
@@ -3421,10 +4354,11 @@
                   int lsb = *sp & 0x0f;
 
                   *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
-                          | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
+                      | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
                   sp++;
                }
             }
+
             else if (row_info->bit_depth == 8)
             {
                sp = row;
@@ -3434,6 +4368,7 @@
                   sp++;
                }
             }
+
             else if (row_info->bit_depth == 16)
             {
                sp = row;
@@ -3447,30 +4382,97 @@
             }
             break;
          }
+
+         default:
+            break;
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_EXPAND_SUPPORTED)
+#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
+/* Encode the alpha channel to the output gamma (the input channel is always
+ * linear.)  Called only with color types that have an alpha channel.  Needs the
+ * from_1 tables.
+ */
+void /* PRIVATE */
+png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structp png_ptr)
+{
+   png_uint_32 row_width = row_info->width;
+
+   png_debug(1, "in png_do_encode_alpha");
+
+   if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
+   {
+      if (row_info->bit_depth == 8)
+      {
+         PNG_CONST png_bytep table = png_ptr->gamma_from_1;
+
+         if (table != NULL)
+         {
+            PNG_CONST int step =
+               (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
+
+            /* The alpha channel is the last component: */
+            row += step - 1;
+
+            for (; row_width > 0; --row_width, row += step)
+               *row = table[*row];
+
+            return;
+         }
+      }
+
+      else if (row_info->bit_depth == 16)
+      {
+         PNG_CONST png_uint_16pp table = png_ptr->gamma_16_from_1;
+         PNG_CONST int gamma_shift = png_ptr->gamma_shift;
+
+         if (table != NULL)
+         {
+            PNG_CONST int step =
+               (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
+
+            /* The alpha channel is the last component: */
+            row += step - 2;
+
+            for (; row_width > 0; --row_width, row += step)
+            {
+               png_uint_16 v;
+
+               v = table[*(row + 1) >> gamma_shift][*row];
+               *row = (png_byte)((v >> 8) & 0xff);
+               *(row + 1) = (png_byte)(v & 0xff);
+            }
+
+            return;
+         }
+      }
+   }
+
+   /* Only get to here if called with a weird row_info; no harm has been done,
+    * so just issue a warning.
+    */
+   png_warning(png_ptr, "png_do_encode_alpha: unexpected call");
+}
+#endif
+
+#ifdef PNG_READ_EXPAND_SUPPORTED
 /* Expands a palette row to an RGB or RGBA row depending
  * upon whether you supply trans and num_trans.
  */
 void /* PRIVATE */
 png_do_expand_palette(png_row_infop row_info, png_bytep row,
-                      png_colorp palette, png_bytep trans, int num_trans)
+   png_const_colorp palette, png_const_bytep trans_alpha, int num_trans)
 {
    int shift, value;
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
-   png_debug(1, "in png_do_expand_palette\n");
-   if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL &&
-#endif
-       row_info->color_type == PNG_COLOR_TYPE_PALETTE)
+   png_debug(1, "in png_do_expand_palette");
+
+   if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
    {
       if (row_info->bit_depth < 8)
       {
@@ -3485,13 +4487,16 @@
                {
                   if ((*sp >> shift) & 0x01)
                      *dp = 1;
+
                   else
                      *dp = 0;
+
                   if (shift == 7)
                   {
                      shift = 0;
                      sp--;
                   }
+
                   else
                      shift++;
 
@@ -3499,6 +4504,7 @@
                }
                break;
             }
+
             case 2:
             {
                sp = row + (png_size_t)((row_width - 1) >> 2);
@@ -3513,6 +4519,7 @@
                      shift = 0;
                      sp--;
                   }
+
                   else
                      shift += 2;
 
@@ -3520,6 +4527,7 @@
                }
                break;
             }
+
             case 4:
             {
                sp = row + (png_size_t)((row_width - 1) >> 1);
@@ -3534,6 +4542,7 @@
                      shift = 0;
                      sp--;
                   }
+
                   else
                      shift += 4;
 
@@ -3541,16 +4550,19 @@
                }
                break;
             }
+
+            default:
+               break;
          }
          row_info->bit_depth = 8;
          row_info->pixel_depth = 8;
          row_info->rowbytes = row_width;
       }
-      switch (row_info->bit_depth)
-      {
-         case 8:
-         {
-            if (trans != NULL)
+
+      if (row_info->bit_depth == 8)
+      {
+         {
+            if (num_trans > 0)
             {
                sp = row + (png_size_t)row_width - 1;
                dp = row + (png_size_t)(row_width << 2) - 1;
@@ -3559,8 +4571,10 @@
                {
                   if ((int)(*sp) >= num_trans)
                      *dp-- = 0xff;
+
                   else
-                     *dp-- = trans[*sp];
+                     *dp-- = trans_alpha[*sp];
+
                   *dp-- = palette[*sp].blue;
                   *dp-- = palette[*sp].green;
                   *dp-- = palette[*sp].red;
@@ -3572,6 +4586,7 @@
                row_info->color_type = 6;
                row_info->channels = 4;
             }
+
             else
             {
                sp = row + (png_size_t)row_width - 1;
@@ -3584,38 +4599,36 @@
                   *dp-- = palette[*sp].red;
                   sp--;
                }
+
                row_info->bit_depth = 8;
                row_info->pixel_depth = 24;
                row_info->rowbytes = row_width * 3;
                row_info->color_type = 2;
                row_info->channels = 3;
             }
-            break;
          }
       }
    }
 }
 
-/* If the bit depth < 8, it is expanded to 8.  Also, if the
- * transparency value is supplied, an alpha channel is built.
+/* If the bit depth < 8, it is expanded to 8.  Also, if the already
+ * expanded transparency value is supplied, an alpha channel is built.
  */
 void /* PRIVATE */
 png_do_expand(png_row_infop row_info, png_bytep row,
-              png_color_16p trans_value)
+    png_const_color_16p trans_color)
 {
    int shift, value;
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
-   png_debug(1, "in png_do_expand\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (row != NULL && row_info != NULL)
-#endif
+   png_debug(1, "in png_do_expand");
+
    {
       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
-         png_uint_16 gray = (png_uint_16)(trans_value ? trans_value->gray : 0);
+         png_uint_16 gray = (png_uint_16)(trans_color ? trans_color->gray : 0);
 
          if (row_info->bit_depth < 8)
          {
@@ -3623,7 +4636,7 @@
             {
                case 1:
                {
-                  gray = (png_uint_16)(gray*0xff);
+                  gray = (png_uint_16)((gray & 0x01) * 0xff);
                   sp = row + (png_size_t)((row_width - 1) >> 3);
                   dp = row + (png_size_t)row_width - 1;
                   shift = 7 - (int)((row_width + 7) & 0x07);
@@ -3631,13 +4644,16 @@
                   {
                      if ((*sp >> shift) & 0x01)
                         *dp = 0xff;
+
                      else
                         *dp = 0;
+
                      if (shift == 7)
                      {
                         shift = 0;
                         sp--;
                      }
+
                      else
                         shift++;
 
@@ -3645,9 +4661,10 @@
                   }
                   break;
                }
+
                case 2:
                {
-                  gray = (png_uint_16)(gray*0x55);
+                  gray = (png_uint_16)((gray & 0x03) * 0x55);
                   sp = row + (png_size_t)((row_width - 1) >> 2);
                   dp = row + (png_size_t)row_width - 1;
                   shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
@@ -3661,6 +4678,7 @@
                         shift = 0;
                         sp--;
                      }
+
                      else
                         shift += 2;
 
@@ -3668,9 +4686,10 @@
                   }
                   break;
                }
+
                case 4:
                {
-                  gray = (png_uint_16)(gray*0x11);
+                  gray = (png_uint_16)((gray & 0x0f) * 0x11);
                   sp = row + (png_size_t)((row_width - 1) >> 1);
                   dp = row + (png_size_t)row_width - 1;
                   shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
@@ -3683,6 +4702,7 @@
                         shift = 0;
                         sp--;
                      }
+
                      else
                         shift = 4;
 
@@ -3690,48 +4710,61 @@
                   }
                   break;
                }
-            }
+
+               default:
+                  break;
+            }
+
             row_info->bit_depth = 8;
             row_info->pixel_depth = 8;
             row_info->rowbytes = row_width;
          }
 
-         if (trans_value != NULL)
+         if (trans_color != NULL)
          {
             if (row_info->bit_depth == 8)
             {
+               gray = gray & 0xff;
                sp = row + (png_size_t)row_width - 1;
                dp = row + (png_size_t)(row_width << 1) - 1;
+
                for (i = 0; i < row_width; i++)
                {
                   if (*sp == gray)
                      *dp-- = 0;
+
                   else
                      *dp-- = 0xff;
+
                   *dp-- = *sp--;
                }
             }
+
             else if (row_info->bit_depth == 16)
             {
+               png_byte gray_high = (png_byte)((gray >> 8) & 0xff);
+               png_byte gray_low = (png_byte)(gray & 0xff);
                sp = row + row_info->rowbytes - 1;
                dp = row + (row_info->rowbytes << 1) - 1;
                for (i = 0; i < row_width; i++)
                {
-                  if (((png_uint_16)*(sp) |
-                     ((png_uint_16)*(sp - 1) << 8)) == gray)
+                  if (*(sp - 1) == gray_high && *(sp) == gray_low)
                   {
                      *dp-- = 0;
                      *dp-- = 0;
                   }
+
                   else
                   {
                      *dp-- = 0xff;
                      *dp-- = 0xff;
                   }
+
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                }
             }
+
             row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
             row_info->channels = 2;
             row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
@@ -3739,20 +4772,23 @@
                row_width);
          }
       }
-      else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_value)
+      else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_color)
       {
          if (row_info->bit_depth == 8)
          {
+            png_byte red = (png_byte)(trans_color->red & 0xff);
+            png_byte green = (png_byte)(trans_color->green & 0xff);
+            png_byte blue = (png_byte)(trans_color->blue & 0xff);
             sp = row + (png_size_t)row_info->rowbytes - 1;
             dp = row + (png_size_t)(row_width << 2) - 1;
             for (i = 0; i < row_width; i++)
             {
-               if (*(sp - 2) == trans_value->red &&
-                  *(sp - 1) == trans_value->green &&
-                  *(sp - 0) == trans_value->blue)
+               if (*(sp - 2) == red && *(sp - 1) == green && *(sp) == blue)
                   *dp-- = 0;
+
                else
                   *dp-- = 0xff;
+
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
@@ -3760,25 +4796,33 @@
          }
          else if (row_info->bit_depth == 16)
          {
+            png_byte red_high = (png_byte)((trans_color->red >> 8) & 0xff);
+            png_byte green_high = (png_byte)((trans_color->green >> 8) & 0xff);
+            png_byte blue_high = (png_byte)((trans_color->blue >> 8) & 0xff);
+            png_byte red_low = (png_byte)(trans_color->red & 0xff);
+            png_byte green_low = (png_byte)(trans_color->green & 0xff);
+            png_byte blue_low = (png_byte)(trans_color->blue & 0xff);
             sp = row + row_info->rowbytes - 1;
             dp = row + (png_size_t)(row_width << 3) - 1;
             for (i = 0; i < row_width; i++)
             {
-               if ((((png_uint_16)*(sp - 4) |
-                  ((png_uint_16)*(sp - 5) << 8)) == trans_value->red) &&
-                  (((png_uint_16)*(sp - 2) |
-                  ((png_uint_16)*(sp - 3) << 8)) == trans_value->green) &&
-                  (((png_uint_16)*(sp - 0) |
-                  ((png_uint_16)*(sp - 1) << 8)) == trans_value->blue))
+               if (*(sp - 5) == red_high &&
+                   *(sp - 4) == red_low &&
+                   *(sp - 3) == green_high &&
+                   *(sp - 2) == green_low &&
+                   *(sp - 1) == blue_high &&
+                   *(sp    ) == blue_low)
                {
                   *dp-- = 0;
                   *dp-- = 0;
                }
+
                else
                {
                   *dp-- = 0xff;
                   *dp-- = 0xff;
                }
+
                *dp-- = *sp--;
                *dp-- = *sp--;
                *dp-- = *sp--;
@@ -3790,28 +4834,57 @@
          row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
          row_info->channels = 4;
          row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,row_width);
+         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
    }
 }
 #endif
 
-#if defined(PNG_READ_DITHER_SUPPORTED)
+#ifdef PNG_READ_EXPAND_16_SUPPORTED
+/* If the bit depth is 8 and the color type is not a palette type expand the
+ * whole row to 16 bits.  Has no effect otherwise.
+ */
 void /* PRIVATE */
-png_do_dither(png_row_infop row_info, png_bytep row,
-              png_bytep palette_lookup, png_bytep dither_lookup)
+png_do_expand_16(png_row_infop row_info, png_bytep row)
+{
+   if (row_info->bit_depth == 8 &&
+      row_info->color_type != PNG_COLOR_TYPE_PALETTE)
+   {
+      /* The row have a sequence of bytes containing [0..255] and we need
+       * to turn it into another row containing [0..65535], to do this we
+       * calculate:
+       *
+       *  (input / 255) * 65535
+       *
+       *  Which happens to be exactly input * 257 and this can be achieved
+       *  simply by byte replication in place (copying backwards).
+       */
+      png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
+      png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
+      while (dp > sp)
+         dp[-2] = dp[-1] = *--sp, dp -= 2;
+
+      row_info->rowbytes *= 2;
+      row_info->bit_depth = 16;
+      row_info->pixel_depth = (png_byte)(row_info->channels * 16);
+   }
+}
+#endif
+
+#ifdef PNG_READ_QUANTIZE_SUPPORTED
+void /* PRIVATE */
+png_do_quantize(png_row_infop row_info, png_bytep row,
+    png_const_bytep palette_lookup, png_const_bytep quantize_lookup)
 {
    png_bytep sp, dp;
    png_uint_32 i;
    png_uint_32 row_width=row_info->width;
 
-   png_debug(1, "in png_do_dither\n");
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-   if (row != NULL && row_info != NULL)
-#endif
-   {
-      if (row_info->color_type == PNG_COLOR_TYPE_RGB &&
-         palette_lookup && row_info->bit_depth == 8)
+   png_debug(1, "in png_do_quantize");
+
+   if (row_info->bit_depth == 8)
+   {
+      if (row_info->color_type == PNG_COLOR_TYPE_RGB && palette_lookup)
       {
          int r, g, b, p;
          sp = row;
@@ -3822,31 +4895,33 @@
             g = *sp++;
             b = *sp++;
 
-            /* this looks real messy, but the compiler will reduce
-               it down to a reasonable formula.  For example, with
-               5 bits per color, we get:
-               p = (((r >> 3) & 0x1f) << 10) |
-                  (((g >> 3) & 0x1f) << 5) |
-                  ((b >> 3) & 0x1f);
-               */
-            p = (((r >> (8 - PNG_DITHER_RED_BITS)) &
-               ((1 << PNG_DITHER_RED_BITS) - 1)) <<
-               (PNG_DITHER_GREEN_BITS + PNG_DITHER_BLUE_BITS)) |
-               (((g >> (8 - PNG_DITHER_GREEN_BITS)) &
-               ((1 << PNG_DITHER_GREEN_BITS) - 1)) <<
-               (PNG_DITHER_BLUE_BITS)) |
-               ((b >> (8 - PNG_DITHER_BLUE_BITS)) &
-               ((1 << PNG_DITHER_BLUE_BITS) - 1));
+            /* This looks real messy, but the compiler will reduce
+             * it down to a reasonable formula.  For example, with
+             * 5 bits per color, we get:
+             * p = (((r >> 3) & 0x1f) << 10) |
+             *    (((g >> 3) & 0x1f) << 5) |
+             *    ((b >> 3) & 0x1f);
+             */
+            p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
+                ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
+                (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
+                (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
+                ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
+                (PNG_QUANTIZE_BLUE_BITS)) |
+                ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
+                ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
 
             *dp++ = palette_lookup[p];
          }
+
          row_info->color_type = PNG_COLOR_TYPE_PALETTE;
          row_info->channels = 1;
          row_info->pixel_depth = row_info->bit_depth;
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,row_width);
-      }
+         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
+      }
+
       else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
-         palette_lookup != NULL && row_info->bit_depth == 8)
+         palette_lookup != NULL)
       {
          int r, g, b, p;
          sp = row;
@@ -3858,269 +4933,52 @@
             b = *sp++;
             sp++;
 
-            p = (((r >> (8 - PNG_DITHER_RED_BITS)) &
-               ((1 << PNG_DITHER_RED_BITS) - 1)) <<
-               (PNG_DITHER_GREEN_BITS + PNG_DITHER_BLUE_BITS)) |
-               (((g >> (8 - PNG_DITHER_GREEN_BITS)) &
-               ((1 << PNG_DITHER_GREEN_BITS) - 1)) <<
-               (PNG_DITHER_BLUE_BITS)) |
-               ((b >> (8 - PNG_DITHER_BLUE_BITS)) &
-               ((1 << PNG_DITHER_BLUE_BITS) - 1));
+            p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
+                ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
+                (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
+                (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
+                ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
+                (PNG_QUANTIZE_BLUE_BITS)) |
+                ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
+                ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
 
             *dp++ = palette_lookup[p];
          }
+
          row_info->color_type = PNG_COLOR_TYPE_PALETTE;
          row_info->channels = 1;
          row_info->pixel_depth = row_info->bit_depth;
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,row_width);
-      }
+         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
+      }
+
       else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
-         dither_lookup && row_info->bit_depth == 8)
+         quantize_lookup)
       {
          sp = row;
+
          for (i = 0; i < row_width; i++, sp++)
          {
-            *sp = dither_lookup[*sp];
+            *sp = quantize_lookup[*sp];
          }
       }
    }
 }
-#endif
-
-#ifdef PNG_FLOATING_POINT_SUPPORTED
-#if defined(PNG_READ_GAMMA_SUPPORTED)
-static int png_gamma_shift[] =
-   {0x10, 0x21, 0x42, 0x84, 0x110, 0x248, 0x550, 0xff0};
-
-/* We build the 8- or 16-bit gamma tables here.  Note that for 16-bit
- * tables, we don't make a full table if we are reducing to 8-bit in
- * the future.  Note also how the gamma_16 tables are segmented so that
- * we don't need to allocate > 64K chunks for a full 16-bit table.
- */
-void /* PRIVATE */
-png_build_gamma_table(png_structp png_ptr)
-{
-  png_debug(1, "in png_build_gamma_table\n");
-  if (png_ptr->gamma != 0.0)
-  {
-   if (png_ptr->bit_depth <= 8)
-   {
-      int i;
-      double g;
-
-      if (png_ptr->screen_gamma > .000001)
-         g = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
-      else
-         g = 1.0;
-
-      png_ptr->gamma_table = (png_bytep)png_malloc(png_ptr,
-         (png_uint_32)256);
-
-      for (i = 0; i < 256; i++)
-      {
-         png_ptr->gamma_table[i] = (png_byte)(pow((double)i / 255.0,
-            g) * 255.0 + .5);
-      }
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
-    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
-      if (png_ptr->transformations & ((PNG_BACKGROUND) | PNG_RGB_TO_GRAY))
-      {
-         g = 1.0 / (png_ptr->gamma);
-
-         png_ptr->gamma_to_1 = (png_bytep)png_malloc(png_ptr,
-            (png_uint_32)256);
-
-         for (i = 0; i < 256; i++)
-         {
-            png_ptr->gamma_to_1[i] = (png_byte)(pow((double)i / 255.0,
-               g) * 255.0 + .5);
-         }
-
-
-         png_ptr->gamma_from_1 = (png_bytep)png_malloc(png_ptr,
-            (png_uint_32)256);
-
-         if (png_ptr->screen_gamma > 0.000001)
-           g = 1.0 / png_ptr->screen_gamma;
-         else
-            g = png_ptr->gamma;   /* probably doing rgb_to_gray */
-
-         for (i = 0; i < 256; i++)
-         {
-            png_ptr->gamma_from_1[i] = (png_byte)(pow((double)i / 255.0,
-               g) * 255.0 + .5);
-         }
-      }
-#endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_RGB_TO_GRAY_SUPPORTED */
-   }
-   else
-   {
-      double g;
-      int i, j, shift, num;
-      int sig_bit;
-      png_uint_32 ig;
-
-      if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
-      {
-         sig_bit = (int)png_ptr->sig_bit.red;
-         if ((int)png_ptr->sig_bit.green > sig_bit)
-            sig_bit = png_ptr->sig_bit.green;
-         if ((int)png_ptr->sig_bit.blue > sig_bit)
-            sig_bit = png_ptr->sig_bit.blue;
-      }
-      else
-      {
-         sig_bit = (int)png_ptr->sig_bit.gray;
-      }
-
-      if (sig_bit > 0)
-         shift = 16 - sig_bit;
-      else
-         shift = 0;
-
-      if (png_ptr->transformations & PNG_16_TO_8)
-      {
-         if (shift < (16 - PNG_MAX_GAMMA_8))
-            shift = (16 - PNG_MAX_GAMMA_8);
-      }
-
-      if (shift > 8)
-         shift = 8;
-      if (shift < 0)
-         shift = 0;
-
-      png_ptr->gamma_shift = (png_byte)shift;
-
-      num = (1 << (8 - shift));
-
-      if (png_ptr->screen_gamma > .000001)
-         g = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
-      else
-         g = 1.0;
-
-      png_ptr->gamma_16_table = (png_uint_16pp)png_malloc(png_ptr,
-         (png_uint_32)(num * png_sizeof (png_uint_16p)));
-
-      if (png_ptr->transformations & (PNG_16_TO_8 | PNG_BACKGROUND))
-      {
-         double fin, fout;
-         png_uint_32 last, max;
-
-         for (i = 0; i < num; i++)
-         {
-            png_ptr->gamma_16_table[i] = (png_uint_16p)png_malloc(png_ptr,
-               (png_uint_32)(256 * png_sizeof (png_uint_16)));
-         }
-
-         g = 1.0 / g;
-         last = 0;
-         for (i = 0; i < 256; i++)
-         {
-            fout = ((double)i + 0.5) / 256.0;
-            fin = pow(fout, g);
-            max = (png_uint_32)(fin * (double)((png_uint_32)num << 8));
-            while (last <= max)
-            {
-               png_ptr->gamma_16_table[(int)(last & (0xff >> shift))]
-                  [(int)(last >> (8 - shift))] = (png_uint_16)(
-                  (png_uint_16)i | ((png_uint_16)i << 8));
-               last++;
-            }
-         }
-         while (last < ((png_uint_32)num << 8))
-         {
-            png_ptr->gamma_16_table[(int)(last & (0xff >> shift))]
-               [(int)(last >> (8 - shift))] = (png_uint_16)65535L;
-            last++;
-         }
-      }
-      else
-      {
-         for (i = 0; i < num; i++)
-         {
-            png_ptr->gamma_16_table[i] = (png_uint_16p)png_malloc(png_ptr,
-               (png_uint_32)(256 * png_sizeof (png_uint_16)));
-
-            ig = (((png_uint_32)i * (png_uint_32)png_gamma_shift[shift]) >> 4);
-            for (j = 0; j < 256; j++)
-            {
-               png_ptr->gamma_16_table[i][j] =
-                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
-                     65535.0, g) * 65535.0 + .5);
-            }
-         }
-      }
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
-    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
-      if (png_ptr->transformations & (PNG_BACKGROUND | PNG_RGB_TO_GRAY))
-      {
-         g = 1.0 / (png_ptr->gamma);
-
-         png_ptr->gamma_16_to_1 = (png_uint_16pp)png_malloc(png_ptr,
-            (png_uint_32)(num * png_sizeof (png_uint_16p )));
-
-         for (i = 0; i < num; i++)
-         {
-            png_ptr->gamma_16_to_1[i] = (png_uint_16p)png_malloc(png_ptr,
-               (png_uint_32)(256 * png_sizeof (png_uint_16)));
-
-            ig = (((png_uint_32)i *
-               (png_uint_32)png_gamma_shift[shift]) >> 4);
-            for (j = 0; j < 256; j++)
-            {
-               png_ptr->gamma_16_to_1[i][j] =
-                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
-                     65535.0, g) * 65535.0 + .5);
-            }
-         }
-
-         if (png_ptr->screen_gamma > 0.000001)
-           g = 1.0 / png_ptr->screen_gamma;
-         else
-           g = png_ptr->gamma;   /* probably doing rgb_to_gray */
-
-         png_ptr->gamma_16_from_1 = (png_uint_16pp)png_malloc(png_ptr,
-            (png_uint_32)(num * png_sizeof (png_uint_16p)));
-
-         for (i = 0; i < num; i++)
-         {
-            png_ptr->gamma_16_from_1[i] = (png_uint_16p)png_malloc(png_ptr,
-               (png_uint_32)(256 * png_sizeof (png_uint_16)));
-
-            ig = (((png_uint_32)i *
-               (png_uint_32)png_gamma_shift[shift]) >> 4);
-            for (j = 0; j < 256; j++)
-            {
-               png_ptr->gamma_16_from_1[i][j] =
-                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
-                     65535.0, g) * 65535.0 + .5);
-            }
-         }
-      }
-#endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_RGB_TO_GRAY_SUPPORTED */
-   }
- }
-}
-#endif
-/* To do: install integer version of png_build_gamma_table here */
-#endif
-
-#if defined(PNG_MNG_FEATURES_SUPPORTED)
-/* undoes intrapixel differencing  */
+#endif /* PNG_READ_QUANTIZE_SUPPORTED */
+#endif /* PNG_READ_TRANSFORMS_SUPPORTED */
+
+#ifdef PNG_MNG_FEATURES_SUPPORTED
+/* Undoes intrapixel differencing  */
 void /* PRIVATE */
 png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
 {
-   png_debug(1, "in png_do_read_intrapixel\n");
+   png_debug(1, "in png_do_read_intrapixel");
+
    if (
-#if defined(PNG_USELESS_TESTS_SUPPORTED)
-       row != NULL && row_info != NULL &&
-#endif
        (row_info->color_type & PNG_COLOR_MASK_COLOR))
    {
       int bytes_per_pixel;
       png_uint_32 row_width = row_info->width;
+
       if (row_info->bit_depth == 8)
       {
          png_bytep rp;
@@ -4128,15 +4986,17 @@
 
          if (row_info->color_type == PNG_COLOR_TYPE_RGB)
             bytes_per_pixel = 3;
+
          else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
             bytes_per_pixel = 4;
+
          else
             return;
 
          for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
          {
-            *(rp) = (png_byte)((256 + *rp + *(rp+1))&0xff);
-            *(rp+2) = (png_byte)((256 + *(rp+2) + *(rp+1))&0xff);
+            *(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);
+            *(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);
          }
       }
       else if (row_info->bit_depth == 16)
@@ -4146,24 +5006,27 @@
 
          if (row_info->color_type == PNG_COLOR_TYPE_RGB)
             bytes_per_pixel = 6;
+
          else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
             bytes_per_pixel = 8;
+
          else
             return;
 
          for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
          {
-            png_uint_32 s0   = (*(rp  ) << 8) | *(rp+1);
-            png_uint_32 s1   = (*(rp+2) << 8) | *(rp+3);
-            png_uint_32 s2   = (*(rp+4) << 8) | *(rp+5);
-            png_uint_32 red  = (png_uint_32)((s0+s1+65536L) & 0xffffL);
-            png_uint_32 blue = (png_uint_32)((s2+s1+65536L) & 0xffffL);
-            *(rp  ) = (png_byte)((red >> 8) & 0xff);
-            *(rp+1) = (png_byte)(red & 0xff);
-            *(rp+4) = (png_byte)((blue >> 8) & 0xff);
-            *(rp+5) = (png_byte)(blue & 0xff);
+            png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);
+            png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);
+            png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
+            png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;
+            png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
+            *(rp    ) = (png_byte)((red >> 8) & 0xff);
+            *(rp + 1) = (png_byte)(red & 0xff);
+            *(rp + 4) = (png_byte)((blue >> 8) & 0xff);
+            *(rp + 5) = (png_byte)(blue & 0xff);
          }
       }
    }
 }
 #endif /* PNG_MNG_FEATURES_SUPPORTED */
+#endif /* PNG_READ_SUPPORTED */