Reading some of the talking-past-each-other dialogue at DPReview about Hybrid Log-Gamma, looking at the curve of it I thought it did a better job of the high end than a bog-standard 2.2 exponential gamma. So, using the magic that is LittleCMS, I took one of Elle’s sRGB profiles and substituted the gamma tone curve with a 1D HLG LUT:
Indeed. I just really did this to stir a pot at DPReview, thread in the Photographic Science and Technology forum on HEIF, wandered into colorspaces and TRCs.
Although, looking at renditions with it from rawproc, I might start using this instead of ‘standard’ sRGB for my export profile…
Interestingly, I had thought that I’d done something similar to this in Commits · Entropy512/elles_icc_profiles · GitHub, but it looks like I didn’t. I can’t remember if this is because HLG can’t be approximated by the various parametric profiles in lcms2 (lcms2 supports a lot of parametric profiles that the ICC standard itself seems to just say “well you can add other parametric formats as extensions”, and I’m not sure what other software implements those extended parametric formats).
I might have implemented an HLG tonecurve-based profile elsewhere, I’m POSITIVE I’ve done it but… I can’t find evidence of me doing it.
I agree that HLG + Rec. 2020 is more “standard” and “typical” than HLG + sRGB (HLG + P3 is a lot less common), however HLG + sRGB primaries has a better chance of “not looking like total garbage” in fallback mode on a non-color-managed application.
HLG is one of the more efficient methods of storing more usable (as in, better than the human banding threshold) dynamic range than sRGB’s transfer function. Sony S-Log2 is actually slightly better, however in practice that’s usually generated by Sony cameras, which don’t let you combine that TRC with Rec. 2020 primaries, and Sony’s S-Gamut colorspaces are WAY too wide for 8 bit encoding leading to annoying color quantization behaviors. Rec. 2020 is pushing things a bit, but overall seems to be one of the best compromises for 8-bit encoding. That’s why setting Sony cameras to HLG mode is popular even when people DO intend to perform further color grading in a video editor.
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