ImageReader : Conform lower case "r", "g", "b" and "a" to upper #5868
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The EXR standard states that it is only the upper case "R", "G", "B" and "A" that have a predefined interpretation, and that is how we treat channels in GafferImage. But in the last week I've received files from two different sources both using lower-case, so this seems worth fixing up on load. In the latter case, the file was from Blender and only the Cryptomatte channels were lowercased. To my surprise, that is actually enshrined in the Cryptomatte specification. I can't find a source for _why_, but based on Psyop/Cryptomatte#35 it seems that _maybe_ it's to disable lossy DWA compression when the DCC won't let you control that per-file or per-part? That seems to call into question the entire idea of using RGBA to represent ID and coverage in the first place, which I believe was originally to play well in apps that only recognised RGBA. In conjunction with GafferHQ#5867, this fixes GafferHQ#5866.
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LGTM - it's no more hacky than any of the other heuristics. |
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The EXR standard states that it is only the upper case "R", "G", "B" and "A" that have a predefined interpretation, and that is how we treat channels in GafferImage. But in the last week I've received files from two different sources both using lower-case, so this seems worth fixing up on load.
In the latter case, the file was from Blender and only the Cryptomatte channels were lowercased. To my surprise, that is actually enshrined in the Cryptomatte specification. I can't find a source for why, but based on Psyop/Cryptomatte#35 it seems that maybe it's to disable lossy DWA compression when the DCC won't let you control that per-file or per-part? That seems to call into question the entire idea of using RGBA to represent ID and coverage in the first place, which I believe was originally to play well in apps that only recognised RGBA.
In conjunction with #5867, this fixes #5866.