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Why 4:2:2 and never 4:4:0?


pietz

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knowing how chroma subsampling works i often ask myself why 4:2:2 is the (semi) professional standard in case 4:4:4 is not an option. it bothers me to imagine that the color information will be full in vertical terms but only half in horizontal direction. and why does everybody use 4:2:2 and nobody ever talks about 4:4:0? why is the vertical color information more important than the horizontal? to my understanding it should be the other way around. since most of the motion in a film is horizontal, shouldnt be the horizontal color information be full instead of the vertical?

somebody here that can elaborate? :) would be highly appreciated.

-Pietz

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This is probably for historical reasons and is related to interlaced video.

With interlaced, each of the two fields is subsampled separately (because the fields represent different time moments and subsampling them the same way as with progressive images would introduce chroma artifacts related to motion). Now, because each field is subsampled separately, if you use one of the subsampling methods with only half the vertical resolution, for example 4:2:0 or 4:4:0, this would result in gaps of two lines with no chroma samples.

Here is how a column of 4 neighbor pixels looks like in this case:

Field 1 Top row (chroma sample)

Field 2 Top row (chroma sample)

Field 1 Bottom row (no chroma sample)

Field 2 Bottom row (no chroma sample)

 

But if you use full vertical sampling, as in 4:2:2, there is no such issue. You only get 1 sample gaps horizontally, and no gaps vertically when applying 4:2:2 to interlaced video.

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wow, this makes complete sense. thank you for your time!

so why is everybody so psyched about 4:2:2 these days? sure its twice as much color information compared to 4:2:0, but i never looked at footage (even graded material) saying "4:2:2 or 4:4:4 would have helped to make this look any better." if the lack of color information bothers you in 4:2:0, it should also bother you in the horizontal of 4:2:2. why favor the quality of vertical color information over horizontal? and yet all editing codec come at least with 4:2:2. i dont get it.

i think it makes a lot of sense to start delivering 10bit to semi professional cameras internally, but 4:2:2 i can easily live without. from what ive experienced theres just no good point in using it...

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with 4:4:4 and 4:2:2 over 4:2:0 it's more than color, it's also brightness. 

So say you shot something too dark, you can brighten it up easier with less noise if you shot at 4:2:2 or 4:4:4

So it is worth it.

Can you make something 4:2:0 look amazing - of course - and you can make something 4:4:4 look terrible.

It's just a nice thing to have.

So is 10-bit or 12-bit color space over 8-bit color space - you have more color to play with.

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