[OctDev] image reading/writing patches

[Debian U. <st...@su...>]

Hi everyone

I recently proposed changing the image reading/writing routines to use
a common image structure.  This patch is an attempt in that direction.

Currently, a gray scale image is a matrix with values in [0,255] while
an RGB image consists of three such gray-scale images.  Some image
routines expect values between [0,1] while others prefer [0,255].  By
using the appropriate numerical classes, I hope to remove this
inconsistency.

The suggested image format (as used by the other brand) is:

Image Type      Matrix Size        Numerical Class
--------------------------------------------------
B&W             MxN                logical
Gray-level      MxN                uint8 or uint16 (depends on depth)
RGB             MxNx3              uint8 or uint16 (depends on depth)

I attach two functions which achieve this: imread2.m (a replacement for
imread.m) and imshow2.m (a wrapper for imshow.m).  'imshow2' can be
installed using dispatch:

  dispatch('imshow', 'imshow2', 'any')

imread2 uses pngread and jpgread when available, or otherwise resorts
to the ImageMagick utilities 'convert' and 'identify'.  Paul mentioned
that we might want to look at libgd.  This is a good idea because of
two reasons I can think of immediately:

1. Fast image loading of multiple formats

While ImageMagick supports many formats, it forces us to convert
images to raw portable gray-maps before loading them into octave.
libgd supports many formats and can be linked directly into an
oct-file.

2. Image manipulation

libgd has built-in support for popular image processing functions,
such as histogram equilization.  Also, lines, text and other
primitives can be drawn onto images.  These functions can simply be
wrapped in .oct files.

I have not updated all the functions in the image toolbox to use the
new format.  I will do so once we all agree on the image structure.  I
would like some ideas on the use of colour-maps and how they fit into
the bigger picture.

Regards
Stefan