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you have to think about chroma unless you are using a 2020cl matrix, which is linear, just like Lab
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Rec2020 has two matrices: linear (Yc'Cbc'Crc') and the traditional non-linear (Y'Cb'Cr'). See page 4 of
ITU-R BT.2020-1. I'm always confused by this stuff, is the following understanding correct?
A dvd/blu-ray is encoded in non-linear Y'Cb'Cr'. So you convert to R'G'B', convert that to linear RGB (= undo gamma) and convert back to linear Yc'Cbc'Crc' [except it's Rec601/709 instead of Rec2020, but that's not the point]. Then you can apply the smoothing and resizing, etc ... ??
I'm a bit puzzled by the derivation of Cbc'Crc' though. I expected it would be something like: Cbc' = (B-Yc')/(1-Kb), but it's not.
@StainlessS, where do you see tau mentioned in the docs? I thought i removed that. Will look at your other issue later.