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YUV is a color space typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, thereby typically enabling transmission errors or compression artifacts to be more efficiently masked by the human perception than using a "direct" RGB-representation. Other color spaces have similar properties, and the main reason to implement or investigate properties of Y'UV would be for interfacing with analog or digital television or photographic equipment that conforms to certain Y'UV standards. The scope of the terms Y'UV, YUV, YCbCr, YPbPr, etc., is sometimes ambiguous and overlapping. Historically, the terms YUV and Y'UV were used for a specific ''analog encoding'' of color information in television systems, while YCbCr was used for ''digital encoding'' of color information suited for video ''and'' still-image compression and transmission such as MPEG and JPEG. Today, the term YUV is commonly used in the computer industry to describe ''file-formats'' that are encoded using YCbCr. The Y'UV model defines a color space in terms of one luma (Y') and two chrominance (UV) components. The Y'UV color model is used in the PAL and SECAM composite color video standards. Previous black-and-white systems used only luma (Y') information. Color information (U and V) was added separately via a sub-carrier 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. Y' stands for the luma component (the brightness) and U and V are the chrominance (color) components; luminance is denoted by Y and luma by Y' – the prime symbols (') denote gamma compression,〔Engineering Guideline EG 28, "Annotated Glossary of Essential Terms for Electronic Production," SMPTE, 1993.〕 with "luminance" meaning perceptual (color science) brightness, while "luma" is electronic (voltage of display) brightness. The YPbPr color model used in analog component video and its digital version YCbCr used in digital video are more or less derived from it, and are sometimes called Y'UV. (CB/PB and CR/PR are deviations from grey on blue–yellow and red–cyan axes, whereas U and V are blue–luminance and red–luminance differences.) The Y'IQ color space used in the analog NTSC television broadcasting system is related to it, although in a more complex way. 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 X Y Z 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.〔CIELUV〕〔CIE 1960 color space〕 ==History== Y'UV was invented when engineers wanted color television in a black-and-white infrastructure.〔Maller, Joe. (RGB and YUV Color ), ''FXScript Reference''〕 They needed a signal transmission method that was compatible with black-and-white (B&W) TV while being able to add color. The luma component already existed as the black and white signal; they added the UV signal to this as a solution. The UV representation of chrominance was chosen over straight R and B signals because U and V are color difference signals. This meant that in a black and white scene the U and V signals would be zero and only the Y' signal would need to be transmitted. If R and B were to have been used, these would have non-zero values even in a B&W scene, requiring all three data-carrying signals. This was important in the early days of color television, because holding the U and V signals to zero while connecting the black and white signal to Y' allowed color TV sets to display B&W TV without the additional expense and complexity of special B&W circuitry. In addition, black and white receivers could take the Y' signal and ignore the color signals, making Y'UV backward-compatible with all existing black-and-white equipment, input and output. It was necessary to assign a narrower bandwidth to the chrominance channel because there was no additional bandwidth available. If some of the luminance information arrived via the chrominance channel (as it would have if RB signals were used instead of differential UV signals), B&W resolution would have been compromised.〔W. Wharton & D. Howorth, ''Principles of Television Reception'', Pitman Publishing, 1971, pp 161-163〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「YUV」の詳細全文を読む スポンサード リンク
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