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The scope of the terms Y′UV, YUV, YCbCr, YPbPr, etc., is sometimes ambiguous and overlapping. Y′UV is the separation used in PAL.; YDbDr is the format used in SECAM and PAL-N, unusually based on non-gamma-corrected (linear) RGB, making the Y component true luminance.
The three values of the YCoCg color model are calculated as follows from the three color values of the RGB color model: [2] [] = [] [] The values of Y are in the range from 0 to 1, while Co and Cg are in the range of −0.5 to 0.5, as is typical with "YCC" color models such as YCbCr.
YCbCr is sometimes abbreviated to YCC.Typically the terms Y′CbCr, YCbCr, YPbPr and YUV are used interchangeably, leading to some confusion. The main difference is that YPbPr is used with analog images and YCbCr with digital images, leading to different scaling values for U max and V max (in YCbCr both are ) when converting to/from YUV.
For example, applying a histogram equalization directly to the channels in an RGB image would alter the color balance of the image. Instead, the histogram equalization is applied to the Y channel of the YIQ or YUV representation of the image, which only normalizes the brightness levels of the image.
Judd was the first to employ this type of transformation, and many others were to follow. Converting this RGB space to chromaticities one finds [4] [clarification needed The following formulae do not agree with u=R/(R+G+B) and v=G/(R+G+B)] Judd's UCS, with the Planckian locus and the isotherms from 1,000K to 10,000K, perpendicular to the locus.
As the value increases above 50%, it has the effect of tinting, and full lightness produces white. At zero saturation, lightness controls the resulting shade of gray. A value of zero still produces black, and full lightness still produces white. The midpoint value results in the "middle" shade of gray, with an RGB value of (128,128,128).
Rec. 2020 allows for RGB and luma-chroma signal formats with 4:4:4 full-resolution sampling and luma-chroma signal formats with 4:2:2 and 4:2:0 chroma subsampling. [2] It supports two types of luma-chroma signals, called YCbCr and YcCbcCrc. YCbCr may be used when the top priority is compatibility with existing SDTV and HDTV operating practices.
A popular way to make a color space like RGB into an absolute color is to define an ICC profile, which contains the attributes of the RGB. This is not the only way to express an absolute color, but it is the standard in many industries. RGB colors defined by widely accepted profiles include sRGB and Adobe RGB.