[Dogway]

Originally Posted by StvG

Quick test changing kb and kr to 0.0722 and 0.2126.

https://imgbox.com/g/MClMislf6m

Results aren't identical but there is no visible difference.

I get kr=0.212649 and kb=0.072182 for Rec709. Also this is the transformation matrix from Rec601 to Rec709, unless I got the SMPTE-C primaries wrong:

0.9395467042922974, 0.017773162573575974, -0.0016219262033700943
0.05017891526222229, 0.9657943844795227, -0.004370423033833504
0.010274499654769897, 0.01643248274922371, 1.0059921741485596

SMPTE-C Primaries:

[0.630,  0.340]
[0.310,  0.595]
[0.155,  0.070]

EDIT: By the way, plot twist. Rec601 doesn't use SMPTE-C based kb and kr coefficients, they kept those from SMPTE 470M, the old 1953 NTSC from the FCC. Those are kr=0.298967, kg=0.586421 and kb=0.114612. Updated the code according.