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Concept
YUV
Résumé
Y′UV, also written YUV, is the color model found in the PAL analogue color TV standard (excluding PAL-N). A color is described as a Y′ component (luma) and two chroma components U and V. The prime symbol (') denotes that the luma is calculated from gamma-corrected RGB input and that it is different from true luminance. Today, the term YUV is commonly used in the computer industry to describe colorspaces that are encoded using YCbCr.
In TV formats, color information (U and V) was added separately via a subcarrier so that a black-and-white receiver would still be able to receive and display a color picture transmission in the receiver's native black-and-white format, with no need for extra transmission bandwidth.
As for etymology, Y, Y′, U, and V are not abbreviations. The use of the letter Y for luminance can be traced back to the choice of XYZ primaries. This lends itself naturally to the usage of the same letter in luma (Y′), which approximates a perceptually uniform correlate of luminance. Likewise, U and V were chosen to differentiate the U and V axes from those in other spaces, such as the x and y chromaticity space. See the equations below or compare the historical development of the math.
The scope of the terms Y′UV, YUV, YCbCr, YPbPr, etc., is sometimes ambiguous and overlapping.
Y′UV is the separation used in PAL.
Y'PbPr is the separation used in component video.
Y′CbCr is any digital encoding of Y'PbPr suited for video and image compression and transmission formats such as MPEG and JPEG.
YDbDr is the format used in SECAM and PAL-N, unusually based on non-gamma-corrected (linear) RGB, making the Y component true luminance.
Y′IQ is the format used in NTSC television.
All these formats are based on a luma component and two chroma components describing the color difference from grey. In all formats other than Y′IQ, each chroma component is a scaled version of the difference between red/blue and Y; the main difference lies in the scaling factors used, which is determined by color primaries and the intended numeric range (compare the use of Umax and Vmax in with a fixed 1/2 in ).
Source officielle
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