Slight change in gray scale values after an ICC profile conversion when using babl color transforms
Submitted by Elle Stone
Created attachment 370824 screenshots of using vs disabling the babl color transforms
This is an obscure bug, but here goes:
- Start GIMP with the babl color transforms disabled using these lines in a "start GIMP" script:
GIMP_COLOR_TRANSFORM_DISABLE_BABL=yes export GIMP_COLOR_TRANSFORM_DISABLE_BABL
Make a 32f linear precision solid white image. Color pick to confirm that the "Pixel" readout is R=G=B=1.000000.
Change the precision to "Perceptual" and then do an ICC profile conversion to my "V4" linear gamma sRGB profile from disk - sRGB-elle-V4-g10.icc
Color pick again, and the "Pixel" readout is still R=G=B=1.000000, as expected, given that the XYZ values in the built-in GIMP sRGB profiles are an exact match to my "on disk" sRGB profiles.
Now close GIMP, comment out the two "DISABLE_BABL" lines in the "start GIMP" script, restart GIMP, and repeat as above. This time, after step 4, the "Pixel" readout is R=G=B=0.999985
I noticed this peculiarity while trying to check how default GIMP handles drawing a gradient on a mask since the latest changes in how layer masks are handled. This is repeatable at will.