ICC profile generation issues

[hpd]

Hello,

We've run into some problems with the content and structure of the ICC profiles created by 'ociobakelut' from the ACES OCIO config.

The issues are reported below.

1. The profile specification version is 4.2.0, but the A2B0 transforms have a black point of 0. This is in violation of the 4.2.0 specification, which requires that perceptual intent transforms render to the v4 perceptual reference medium, which is defined in section 6.3.3 of ICC.1 2004-10 (the 4.2.0 spec.)
   • This issue could be addressed by packaging the transforms as v2 A2B0 tags and changing the specification version to 2.x.x
2. The chad tags in the profiles are all identical, and convert the PCS white point to XYZ = {0.950153, 1.00013, 1.0884} in the device space. I do not think this is correct for the following reasons:
   • The chad tag matrix is supposed to be normalized so the converted Y value is 1.
   • The device space normalized tristimulus values are close to D65 but not exactly D65, which does not make sense. I would think the device space normalized tristimulus values should be as follows: DCDM, P3-D60, Rec.709 (D60 sim.), sRGB (D60 sim.) - D60 P3-DCI - DCI white point Rec.709, Rec.2020 - D65
   • This issue could be addressed by either correcting the chad tags, or by removing them and indicating a profile specification version of 2.0.0.
3. The B2A0 transforms do not invert the A2B0 transforms.
   • This issue will need to be addressed by providing inverse transforms which roundtrip with reasonable accuracy over the gamut and dynamic range of the specified output device.

The ACES OCIO config currently lives in my fork https://github.com/hpd/OpenColorIO-Configs/tree/master/aces_1.0.0

An example command line used to generate the ICC profiles in the baked/photoshop folder is as follows: ociobakelut --iconfig config/config.ocio -v --inputspace ACEScc --outputspace "Rec.709 - Full" --description "ACES 1.0 Output - Rec.709 - Full for ACEScc data" --shaperspace "Output Shaper" --shapersize 1024 --cubesize 33 --format icc "config/baked/photoshop/Rec.709 - Full for ACEScc.icc"

• We should use the whitepoint flag here.

Thanks for your help, HP