Editing Chroma subsampling (section)

=== Different Cb and Cr rates ===
A number of legacy schemes allow different subsampling factors in Cb and Cr, similar to how a different amount of bandwidth is allocated to the two chroma values in broadcast systems such as [[CCIR System M]]. These schemes are not expressible in ''J:a:b'' notation. Instead, they adopt a ''Y:Cb:Cr'' notation, with each part describing the amount of resolution for the corresponding component. It is unspecified whether the resolution reduction happens in the horizontal or vertical direction.

* In JPEG, 4:4:2 and 4:2:1 half the vertical resolution of ''Cb'' compared to 4:4:4 and 4:4:0.<ref>{{cite web |title=Support decoding yuv442 and yuv421 jpeg images. · FFmpeg/FFmpeg@387d860 |url=https://github.com/FFmpeg/FFmpeg/commit/387d86077f5237e53cec7a4ed31f5531224feebf |website=GitHub |language=en}}</ref> 
* In another version of {{vanchor|4:2:1}}, '''Cb''' horizontal resolution is half that of '''Cr''' (and a quarter of the horizontal resolution of '''Y''').
* 4:1:0.5 or 4:1:0.25 are variants of 4:1:0 with reduced horizontal resolution on Cb, similar to VHS quality.