YUV is a basic color model used in analog color TV broadcasting, YCbCr is a scaled and offset version of the YUV color space, used in digital video applications.(Reference:Video Demysitified, p.19)
Component Video is known as YPbPr. YPbPr is the analog version of YCbCr digital video. (YCbCr is often called YPbPr when used for analog component video)
The YUV color space is used by the PAL (Phase Alternation Line), NTSC (National Television System Committee), and SECAM (Sequentiel Couleur Avec Mémoire or Sequential Color with Memory) composite color video standards. The black-and-white system used only luma (Y) information; color information (U and V) was added in such a way that a black-and-white receiver would still display a normal black-and-white picture.(Reference:Keith Jack(2007) Video Demysitified, 4th Ed p.17)
The YCbCr color space was developed as part of ITU-R BT.601 during the development of a world-wide digital component video standard (discussed in Chapter 4). YCbCr is a scaled and offset version of the YUV color space. Y is defined to have a nominal 8-bit range of 16–235; Cb and Cr are defined to have a nominal range of 16–240. There are several YCbCr sampling formats, such as 4:4:4, 4:2:2, 4:1:1, and 4:2:0.(Reference:Keith Jack(2007) Video Demysitified, 4th Ed p.19)
The various subsampling formats can be pictorially described as follows:
Source:Borivoje Furht Encyclopedia of multimedia p.875
The YCbCr 4:4:4 format has four Cb and four Cr pixels for every 2x2
block of Y pixels, the YCbCr 4:2:2 format has two Cb and two Cr pixels for every 2x2
block of Y pixels, and the YCbCr 4:2:0 format has one Cb and one Cr pixels for every 2x2
block of Y pixels. All the three formats have the Y component at the full picture
resolution. The difference in the formats is that the YCbCr 4:2:2 and YCbCr 4:2:0 formats
have the chroma components at a reduced resolution. The human eye cannot perceive
the difference when chroma is sub sampled. In fact, even the YCbCr 4:2:0 format with
chroma V4 of the luma resolution is sufficient to please the human eye. The YCbCr 4:2:0
format is the predominantly used format and is used in applications such as DVD, digital
TVs, and HDTVs. The YCbCr 4:2:2 is typically used for studio quality applications and
YCbCr 4:4:4 is hardly used. The use of YCbCr 4:2:0 instead of the RGB color space
represents a 50% reduction in image size and is a direct result of exploiting the
perceptual redundancies of the human visual system.( quoted from: Borivoje Furht Encyclopedia of multimedia p.875)
Source: David J. Katz, Rick Gentile Embedded media processing , p.200
Packed and Planar Formats:
YUV formats fall into two distinct groups, the packed formats where Y, U (Cb) and V (Cr) samples are packed together into macropixels which are stored in a single array, and the planar formats where each component is stored as a separate array, the final image being a fusing of the three separate planes. (Ref: fourcc.org )
Subsampling intervals in the horizontal and vertical directions may merit some explanation. The horizontal subsampling interval describes how frequently across a line a sample of that component is taken while the vertical interval describes on which lines samples are taken. For example, UYVY format has a horizontal subsampling period of 2 for both the U and V components indicating that U and V samples are taken for every second pixel across a line. Their vertical subsampling period is 1 indicating that U and V samples are taken on each line of the image. (Ref: fourcc.org )
See also: Discussion of YUV subsampling in The image processing handbook p.36
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