chroma subsampling images

4:4:4 (Cb/Cr Same as Luma) Cb and Cr are sampled at the same full rate as the luma. MPEG-2 supports 4:4:4 coding, but having the same number of color difference samples as the luma is considered overkill and not worth the additional bandwidth to transmit it. When video is converted from one color space to another, it is often resampled to 4:4:4 first.

4:2:2 (1/2 the Luma Samples) Cb and Cr are sampled at half the horizontal resolution of Y. Co-sited means that Cb/Cr samples are taken at the same time as Y. 4:2:2 color sampling is widely used and considered very high quality. It is used for prosumer and professional digital video recording, including DV (at 50 Mbps), Digital Betacam and DVCPRO 50 and is an option in MPEG-2.

4:1:1 (1/4 the Luma Samples) Cb and Cr are sampled at one quarter the horizontal resolution. Co-sited means that Cb/Cr samples are taken at the same time as the Y. Co-sited 4:1:1 is used in DV, DVCAM and DVCPRO formats.

4:2:0 (1/4 the Luma Samples) The zero in 4:2:0 means that Cb and Cr are sampled at half the vertical resolution of Y. MPEG-1 and MPEG-2 use 4:2:0, but the samples are taken at different intervals. By the time MPEG-2 came along, it was known that 4:2:2 coding was often converted to 4:2:0, which is why MPEG-2 sampling more closely lines up with the 4:2:2 pattern. H.261/263 also uses 4:2:0. Analog Too Engineers use the 4:n:n nomenclature loosely to refer to relative bandwidths of analog signals. For example, if digital RGB signals (computer graphics) are converted to analog color difference signals (YPbPr), it starts off at 4:4:4 YPbPr. When appropriately filtered prior to sampling, it might be characterized as 4:2:2 YPbPr, which is not an accurate use of the terminology because it is not digital, but it is used. See YCbCr, ITU-R BT.601 and YUV.

Analog or Digital?

No wonder confusion reigns. These outputs on the back of this DVD player are analog, correctly identified as Y, Pb and Pr, not the digital Y, Cb and Cr.

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