[Gimp-developer] (no subject)

[Elle Stone <l elle stone gmail com>]

Hello Gimp Developers,

I compiled Gimp, Babl, and Gegl from git (last compilation was June
12, 2012) and did some testing. I posted my findings to a temporary
web page: http://ninedegreesbelow.com/temp/gimp29.html

I do understand that Gimp 2.9 from git is undergoing heavy development
and so it changes frequently. My apologies if I'm reporting on stuff
you already know. But here is a summary of what I've found so far:

(1) Color space conversions result in lost colors, whether done at 8-,
16-, or 32-bits, floating or integer. At first I thought it was a
result of converting to and from a linear-gamma color space. But
actually the color space gamma makes no difference.

(2) All the color space conversions that I used involved matrix
profiles. For a matrix profile, the only valid type of color space
conversion is "colorimetric". I used "relative colorimetric" color
space conversion exclusively. The color space conversion results
varied depending on whether I used black point compensation or not.
However, if the color spaces involved all have the same black point,
using or not using black point compensation should not make any
difference whatsoever.

(3) Eric Brasseur's image scaling test produced very odd image
discolorations, regardless of what color space (linear or nonlinear
gamma) or image depth (8-bit integer or 32-bit floating) was used.

(4) Although Gimp 2.9 correctly opens 8-bit tiffs, when opening any
16-bit tiff, the image is subjected to a roughly gamma=2.2 curve. All
RGB colors are altered (it's not just a display problem), so the
resulting image is too light.

Again, my apologies if I'm reporting issues of which you are already aware.

Kind regards,
Elle Stone