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YPbPr or Y'PbPr, also written as YPBPR, is a color space used in video electronics, in particular in reference to component video cables. YPbPr is the analog version of the YCbCr color space; the two are numerically equivalent but YPbPr is designed for use in analog systems while YCbCr is intended for digital video.
YPbPr is commonly referred to as component video by manufacturers; however, there are many types of component video, most of which are some form of RGB. Some video cards come with video-in video-out (VIVO) ports for connecting to component video devices.
YPbPr is converted from the RGB video signal, which is split into three components: Y, PB, and PR.
- Y carries luma (brightness or luminance) and synchronization (sync) information. Y = 0.2126 R + 0.7152 G + 0.0722 B. Before the advent of color television, the Y axis on an oscilloscope display of a video waveform represented the intensity of the scan line. With color, Y still represents intensity but it is a composite of the component colors.
- PB carries the difference between blue and luma (B − Y).
- PR carries the difference between red and luma (R − Y).
To send a green signal as a fourth component is redundant, as it can be derived using the blue, red and luma information.
When color signals were first added to the NTSC-encoded black and white video standard, the hue was represented by a phase shift of a color reference sub-carrier. P for phase information or phase shift has carried through to represent color information even in the case where there is no longer a phase shift used to represent hue. Thus, the Y PB PR nomenclature derives from engineering metrics developed for the NTSC color standard.
The same cables can be used for YPbPr and composite video. This means that the yellow, red, and white RCA connector cables commonly packaged with most audio/visual equipment can be used in place of the YPbPr connectors, provided the end user is careful to connect each cable to corresponding components at both ends. Also, many TVs use the green connection either for luma only or for composite video input. Since YPbPr is backwards compatible with the luminance portion of composite video even with just component video decoding one can still use composite video via this input, but only luma information will be displayed, along with the chroma dots. The same goes the other way around so long as 480i or 576i is used.
Signals that use YPbPr offer enough separation that no color multiplexing is needed, so the quality of the extracted image is nearly identical to the signal before encoding. S-Video and composite video mix the signals together by means of electronic multiplexing (though S-Video does far better as it gives the whole video bandwith to luma and transmits chroma separately); however, more often than not the signal is degraded at the display end as (unless S-Video is used) the display is not able to separate the signals completely, although newer HDTVs (at least from reputable brands) tend to do a much better job at separation than most CRT TVs. Nevertheless it is possible for their multiplexed counterparts to interfere with each other (see dot crawl).
- Color FAQ, Charles Poynton