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RE: 601 versus 709 (formerly YUV/RGB) Color Space Issues



As Bill Miller of SMPTE/ABC points out, there are two effects of the
different matrices - one is the colorimetry, which some people believe is
quite perceptible (and many don't).  The other is the fact that the chroma
components are typically filtered and then resampled (from 4:4:4 to 4:2:2).
One of these matrices pushes a lot of green information into the "2:2"
channels; the low pass filtering then results in a VERY noticeable loss of
resolution when the imagery is finally reconstructed back up to 4:4:4 RGB
space for final display and consumption.

Actually, there is a third combined effect that makes it all much worse.
Assuming everything's gone digital, the numeric precision of all of the
concatenated transforms mentioned above coupled with the limited dynamic
range of the "16 to 235" problem (and potentially negative values in some
implementations) produces even more obvious changes between the two matrix
domains when you go through the whole transfer function and then try to
match two clips.

This whole thing is a real mess.



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