Make Khronos PBR Neutral invertable #4716
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See if you can tell the difference. Updated: The largest output difference due to this change (not this image, but for all possible input colors) is less than 1%. |
romainguy
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Mar 18, 2024
Based on model-viewer's change at google/model-viewer#4716
romainguy
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Based on model-viewer's change at google/model-viewer#4716
JL-Vidinoti
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Apr 22, 2024
* verified inverse * update Khronos PBR Neutral tone mapper * update docs
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Feedback from Autodesk was that the ability to analytically invert a tone mapping function has a lot of important use cases through the industry. It turns out my tone mapper was quite difficult to invert, but a very small and almost imperceptible change made it trivial to invert. The key is making the desaturation step not change the compressed brightness value, so instead of mixing toward pure white
[1, 1, 1], instead go towardpeak * [1, 1, 1]. Anywhere the mix is significant,peakis already very close to 1, so this is a minor change, but it helps enormously with invertibility since these asymptotes become so sensitive when inverted.I've included an analytical inverse function in
lut-writer.mjsand verified the round-trip relative error is less than2e-10.