Re: [Gimp-print-devel] Printing RGB layers in B&W.

[Robert L K. <rl...@al...>]

   Date: Wed, 01 Mar 2000 12:28:22 +0000
   From: Dave Hill <da...@mi...>

   The problem seems to be that after you have merged the layers
   (which you have to do by hand in Gimp 1.0.4), the image is
   "RGB-Alpha". If you just draw on the background, the image is
   "RGB" and works OK. So the problem is in "rgb_to_gray()" which
   isn't handling the alpha channel properly.

OK, I think I know what's wrong here.  I was dividing by the wrong
constant.  I believe that this happened initially when I was
converting everything from 8 to 16 bits of precision.  Around 1.74 I
"fixed" the constant from 25500 to 255, which was incorrect.  I've
tested this and committed it to the mainline (at first I thought the
constant was supposed to be 100, but that definitely didn't work :-)

Mitch or Sven, could you apply this to 3.0 when you get

diff -u -r1.79 print-util.c
--- print-util.c        2000/02/29 02:59:14     1.79
+++ print-util.c        2000/03/01 12:47:41
@@ -809,7 +809,7 @@
          *gray = vars->lut.composite[((rgb[0] * LUM_RED +
                                        rgb[1] * LUM_GREEN +
                                        rgb[2] * LUM_BLUE) *
-                                      rgb[3] / 255 + 255 - rgb[3])];
+                                      rgb[3] / 25500 + 255 - rgb[3])];
          gray ++;
          rgb += bpp;
          width --;

-- 
Robert Krawitz <rl...@al...>      http://www.tiac.net/users/rlk/

Tall Clubs International  --  http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail lp...@uu...
Project lead for The Gimp Print --  http://gimp-print.sourceforge.net

"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton