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phil harbath
4:4:4
on Jun 11, 2004 at 8:04:57 pm

could someone please explain the difference between 4:4:4, and 4:2:2. are most video playback cards 4:2:2?

thanks
phil harbath
jamination


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tquinn
Re: 4:4:4
on Jul 19, 2004 at 9:46:38 pm

Phil,

Sorry, the physicist has to reply.

4:4:4 and 4:2:2 are shorthand experessions for digital video standards. The numbers specifially refer to the sampling frequency ratios for, respectively, the luminance and color difference components (Y, R-Y, B-Y) of a component video signal

Thus a 4:4:4 format takes twice as many chrominance samples per unit time as a 4:2:2. Generally, 4:2:2 is considered better than the average person can see (and so really the "standard" for high-quality sampling. 4:4:4 is the "gold standard" of sampling and you'll usually only see it in really high end studio-type systems or systems where the engineer knows that she / he is going to do a LOT of fiddiling and converting later.

This is all described in an absolutely riveting technical specification known, endearingly, as ITU-R BT.601-5, and available at: http://www.itu.int/home/index.html (for a small fee.)

HINT: The most important reason for you to pay attention to this spec is that 4:2:2 is (at least IMHO) the lowest you'll want to go if you intend to do any downstream chroma-keying with your video. 4:1:1 won't chroma-key well.

Have Fun

Thomas


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