Notice of Meeting - ACES Gamut Compression Implementation VWG - Meeting #17 - July 22, 2021

ACES Gamut Compression Implementation VWG Meeting #17

Thursday, July 22, 2021
9:30 - 10:30am Pacific Time

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  • Focusing on fleshing out the User Guide before the Implementation Guide - as we’ve got a few implementations coming out soon
  • CLF test pattern is good, but with very large values as well as NaNs and infs - which aren’t good for the gamut compression.
  • @nick has designed one for our uses, with patches & ramps of hue and saturation sweeps.
  • Then run the oiiotool command line comparison with the relative difference settings set by the CLF group.
  • @nick will post the oiiotool and the python code to generate the test image.
  • @joseph - do we also want to test with highly saturated commercial colors (Coke red, etc)
  • Should we ship a plotting tool / visual comparison aide? Possibly a colab using the python colour science library?


Here is a link to a Google Colab version of the code to generate (a slightly tweaked version of) the test pattern I showed in the meeting. It also includes CIExy plots of the original and compressed pattern.

Because OpenImageIO is needed to write an ACES compliant EXR, and that will nor run in a Colab, I have commented out the OpenImageIO based lines, and added some code which uses ImageIO to write a 32-bit PIZ compressed EXR.

Here is a proper ACES EXR of the test pattern, together with gamut compressed versions made using ctlrender and BlinkScript.

For testing an implementation the following command line (based on what @ChrisD and @doug_walker created for the CLF VWG) should be used:

oiiotool gc_test_image_v006_comp_ctl.exr --dup gc_test_image_v006_comp_blink.exr --absdiff --swap --abs --maxc 0.1 --div --rangecheck 0,0,0 .002,.002,.002 -o /tmp/tmp.exr

This will produce the following output if the images match:

       0  < 0,0,0
       0  > .002,.002,.002
 2073600  within range

We would be grateful if people could take a look at the proposed test pattern, so we can get feedback for discussion in this week’s meeting. In particular, input from @michaelch, @bill, @ptr, @daniele and @doug_walker would be greatly appreciated.

Here is an updated version of the Colab where the image is displayed with an (approximate) sRGB Output Transform before and after gamut compression.