[PD] Colour in Digital Video

Mathieu Bouchard matju at artengine.ca
Fri Dec 21 21:04:05 CET 2007

On Fri, 21 Dec 2007, vade wrote:

> These reduced candences can significantly effect any attempts to do good 
> chromakeying or color work, why after effects and other applications that are 
> not strictly editors typically work at 4:4:4 RGB. Anyway, Its definitely an 
> interesting to know, and can significantly help make footage you are working 
> with look better.

Yeah, I've encountered problems with that. GridFlow naturally treats all 
YUV as 4:4:4, but I was still inputting from a YUV 4:2:0 stream which was 
a recombination of a RGBG (double green) matrix. The RGBG thing is similar 
to YUV 4:2:2 as you get more resolution for one channel than the other, 
but because this is not the same channel, some further information is 
lost, and on top of that, YUV 4:2:0 discards even more information 
compared to YUV 4:2:2 or RGBG. This caused me trouble for an application 
that was very relying on the chroma... you can think of it as a chroma 
key, though I was not using it to make transparencies nor even any video 

> P.S., there was some discussion concerning the difference of human 
> genetics not being accounted for.

I only mentioned it briefly and so far you're the first one to actually 
exchange about it. (I've always found it weird that the word "discussion" 
is used for something in which there are not already two persons 
exchanging, but quite a few textbooks use it like that, so...)

> The older broadcast formats for NTSC/PAL and SECAM are not ... final, 
> per se. There are variants of all of these, and the YUV components can 
> vary quite differently depending on what version of NTSC/PAL etc you 
> want to use in what nation/geography.

I don't think that most of the difference is in genetics of whole 
populations. It might be plain statistical error due to the sample size or 
the choice of the sample, or it could be the way to extract a typical 
measure (mean vs median vs mode), or it could be an instrumentation error 
(or just a choice in how it should be done, in the case where it's not 
clear that only one way is not a mistake), for example, filtering out high 
violet by using the wrong kind of glass (it happened).

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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada

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