I’ve just pushed CAM DRT v042-pex3 to my repo.
v042-pex3 version brings the following changes:
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New chroma scaling with the exponent suggested by @luke.hellwig.
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New in-gamut compression algorithm that matches the look of the previous versions. It first expands colorfulness a little bit in the darker colors, and then compresses to create the path to white. The in-gamut compression no longer pushes values outside spectral locus (or is minimal compared to previous versions).
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New HDR/SDR appearance match technique. The old technique of rescaling the tonescale to bring the chroma scaling ratios closer to 100 nits tonescale is no longer used. Instead, the ratios are used as is and the tonescale is not touched. The match is created by scaling the in-gamut compression parameters automatically by the peak luminance. This is simpler than the previous one.
LUTs
LUTs and DCTLs are available in my repo for Rec.709, Rec.709 sim and Rec.2100 P3Limited.
Look compared to v035
v042-pex3:
v035:
Effect of in-gamut compression to values close to spectral locus
Input image:
Input chromaticities:
Scaled chromaticities (using the new exponent):
Fully chroma compressed chromaticities:
Then comparing to v035. v035 fully chroma compressed chromaticities:
The last two images show the difference between v042-pex3 and v035, and the problem that the older versions had that @alexfry has been talking about. In v042-pex3 the chromaticities are no longer pushed outward, or is only minimal compared to older versions.