YPbPr or ${\displaystyle Y'P'bP'r}$, also written as YP_BP_R, is a color space used in video electronics, in particular in reference to component video cables. Like YC_BC_R, it is based on gamma corrected RGB primaries; 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.^[1]

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.

History

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. The "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.^{[citation needed]}

Usage

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 backward 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 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.

Technical details

${\displaystyle Y'P'bP'r}$ can be derived from a gamma corrected ${\displaystyle R'G'B'}$ signal with a typical range of 0-700 mV. The first step is converting to ${\displaystyle Y'}$, ${\displaystyle R'-Y'}$ and ${\displaystyle B'-Y'}$.^[2]

${\displaystyle Y'}$carries luma (brightness or luminance) and synchronization (sync) information. Luma is defined as:

• ${\displaystyle Y'=0.212R+0.701G+0.087B}$ for Hi-Vision;
• ${\displaystyle Y'=0.2126R+0.7152G+0.0722B}$ for HDTV;
• ${\displaystyle Y'=0.299R+0.587G+0.114B}$ for SDTV;

${\displaystyle R'-Y'}$carries the difference between red and luma, defined as:

• ${\displaystyle R'-Y'=0.7874R'-0.7152G'-0.0722B'}$for Hi-Vision and HDTV;
• ${\displaystyle R'-Y'=0.701R'-0.587G'-0.114B'}$ for SDTV.

${\displaystyle B'-Y'}$carries the difference between blue and luma, defined as:

• ${\displaystyle B'-Y'=-0.2126R'-0.7152G'+0.9278B'}$ for Hi-Vision and HDTV;
• ${\displaystyle B'-Y'=-0.299R'-0.587G'+0.886B'}$ for SDTV.

These ${\displaystyle R'-Y'}$ and ${\displaystyle B'-Y'}$ values are then scaled to obtain normalized ${\displaystyle P'r}$ and ${\displaystyle P'b}$ values in the range of +/- 350 or 0-700 mV:^[2][3]

• ${\displaystyle P'b=(B'-Y')/1.826}$ and ${\displaystyle P'r=(R'-Y')/1.576}$ for Hi-Vision;
• ${\displaystyle P'b=[0.5/(1-0.0722)](B'-Y')}$ and ${\displaystyle P'r=[0.5/(1-0.2126)](R'-Y')}$ for HDTV;
• ${\displaystyle P'b=0.564(B'-Y')}$ and ${\displaystyle P'r=0.713(R'-Y')}$ for SDTV.

These formula are based on SMPTE 240M (240M defined EOTF and uses SMPTE 170M primaries and white point) for Hi-Vision; BT.601 matrix for 525 lines (SMPTE 273M) and 625 lines (ITU-R BT.1358) for SDTV; and SMPTE 274M and SMPTE 296M for HDTV.^[4]

The following table lists example YP_BP_R values for black, 50% gray and full intensity colors, as defined in ITU-R Recommendation BT.1729:^[3]

To send a green signal as a fourth component is redundant, as it can be derived using the blue, red and luma information.

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, but in HD formats a tri-level sync is used and is typically carried on all channels.^[4]

See also

Graphic chipsets that generate color internally based on YP_BP_R:

• CTIA and GTIA
• MOS Technology VIC
• MOS Technology VIC-II
• MOS Technology TED
• TMS9918
• Motorola 6847

References

External links

• Color FAQ, Charles Poynton