A reduction of color resolution in digital component video signals in order to accommodate limited storage and bandwidth. The color components are compressed by sampling them at a lower rate than the brightness (luma). Although color information is actually discarded, human eyes are less sensitive to the color components in a video signal than they are to the brightness.
YCbCr Is the Digital Equivalent of YUV
The YUV color space is encoded digitally as YCbCr. The Y is the luma in both, and Cb and Cr are the U and V color difference signals (for details, see YUV).
YCbCr Is Designated as 4:n:n
The 4 is the sampling rate, and the next two "n" digits are the Cb and Cr rate. Review the illustrations below. Each 8x8 matrix represents a "macroblock" of 64 pixels in a video frame. The pink squares are the pixel locations where the sample is taken. Sony's HDCAM uses a different notation because it compresses both the luma and the colors (see 3:1:1).
4:4:4 (Full Rate)
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. Considered very high quality, 4:2:2 is used for prosumer and professional 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.
Engineers use the 4:n:n nomenclature loosely to refer to relative bandwidths of analog signals. For example, if digital RGB signals in the computer are converted to analog color difference signals (YPbPr), they start out at 4:4:4 YPbPr. When filtered prior to sampling, they might be characterized as 4:2:2 YPbPr. See YPbPr
Analog or Digital?
Slightly confusing because the outputs on the back of this DVD player are analog, correctly identified as Y, Pb and Pr, not the digital Y, Cb and Cr.