Y/Pb/Pr

YPbPr or Y'PbPr, also written as , is a color space used in video electronics, in particular in reference to component video cables. YP_BP_R is gamma corrected YC_BC_R color space (it is not analog YUV that was used for analog TV, though component video is an analog interface); the two are numerically equivalent but YP_BP_R is designed for use in analog systems while YC_BC_R is intended for digital video. The EOTF (gamma correction) may be different from common sRGB EOTF and BT.1886 EOTF. Sync is carried on the Y channel and is a bi-level sync signal, however, in HD formats a tri-level sync is used and is typically carried on all channels.

YP_BP_R 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.

Technical details

YP_BP_R is converted from the RGB video signal, which is split into three components: Y, P_B, and P_R.
* Y carries luma (brightness or ''luminance'') and synchronization (sync) information. Luma is defined as $Y = 0.2126 R + 0.7152 G + 0.0722 B$ in SMPTE 274M (1920x1080 resolution) and SMPTE ST 296 (1280x720). It uses BT.709-2 matrix coefficients and digital YC_BC_R. 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.
* P_B carries the difference between blue and luma ( B − Y).
* P_R carries the difference between red and luma ( R − Y).
There are other standards of YP_BP_R components derivation available: 1920x1035 uses SMPTE 240M (240M defined EOTF and uses SMPTE 170M primaries and white point) and 525 lines 60/1.001 Hz (SMPTE 273M) and 625 lines 50 Hz ( ITU-R BT.1358) BT.601 matrix is used.

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 YP_BP_R nomenclature derives from engineering metrics developed for the NTSC color standard.

The same cables can be used for YP_BP_R 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 YP_BP_R 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 YP_BP_R 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.

YP_BP_R advantages

Signals using YP_BP_R offer enough separation that no color multiplexing is needed, so the quality of the extracted image is nearly identical to the pre-encoded signal. S-Video and composite video mix the signals together by means of electronic multiplexing. Signal degradation is typical for composite video, as most display systems are unable to completely separate the signals, though HDTVs tend to perform such separation better than most CRT units (see dot crawl). S-Video can mitigate some of these potential issues, as its luma is transmitted separately from chroma.

Among consumer analog interfaces, only YP_BP_R and analog RGB component video are capable of carrying non-interlaced video and resolutions higher than 480i or 576i, up to 1080p for YP_BP_R.

References

External links

Color FAQ
Charles Poynton

{{Color space

Color space
Video signal

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