xvYCC

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xvYCC or Extended-gamut YCC is a color space used in the video electronics of flat panel television sets, supporting 1.8 times as many colors as the sRGB color space.[1] xvYCC was specified by the IEC in October 2005 and published in January 2006 as IEC 61966-2-4. The wider spectrum of LED backlighting replacing cold cathodes has enabled this extension of the LCD display color gamut.

xvYCC uses the full range of values (1 to 254 in an 8-bit space) to represent colors. In BT.601 and BT.709, RGB colors are represented only by 8-bit values from 16 to 235. This limited range was established to allow for undershoot and overshoot, attributes of analog TV signaling. With digital TV signaling, there is no undershoot or overshoot, and the values from 1-15 and 235-254 can be used to represent real colors. In order to maintain backward-compatibility with earlier standards, the red (R), green (G), blue (B) and white standard colors are still calculated at the same indices in the color space. The wider ranges of digital values allow representation of deeper greens, deeper reds, and deeper blues - and of course intermediate colors previously beyond the boundary limit in the CCIR 601 color space.

Even the high-definition television color space defined by BT.709 encompasses only 45 per cent of the possible values with RGB indices of 1 to 254, since those indices are limited to 16 to 234 by the BT spec. The xvYCC standard uses 1 to 254, and can encode more than twice the number of color values. (The sRGB system is in between the BT.709 and xvYCC systems, allowing use of all combinations of R, G and B values from 16 to 235 - more combinations, but not so many as in xvYCC.)

In a paper published by Society for Information Display in 2006, the authors mapped the 769 colors in the Munsell Color Cascade to the BT.709 space and to the xvYCC space. 55% of the Munsell colors could be mapped to the sRGB gamut, but 100% of those colors could map to the xvYCC gamut.[2] Deeper hues can be created - for example a deeper red by giving the opposing color (green) a negative coefficient.

A mechanism for carrying the gamut boundary definition for xvYCC has been defined in the HDMI 1.3 Specification. Although HDMI 1.3's other new color feature, Deep Color, is not required to transport xvYCC color information, it is commonly associated with xvYCC because these features are used together in high-end CE systems to improve the viewing image quality. Above 480p and 576p, Deep Color systems should use Category 2 HDMI cables (indicated by a logo), which are qualified for link clock rates above 75MHz.[3]

[edit] References

  1. ^ HDMI 1.3 Update. HDMI Licensing (2006). Retrieved on 2006-08-30.
  2. ^ Tatsuhiko Matsumoto, Yoshihide Shimpuku, Takehiro Nakatsue, Shuichi Haga, Hiroaki Eto, Yoshiyuki Akiyama, and Naoya Katoh (2006). "19.2: xvYCC: A New Standard for Video Systems using Extended-Gamut YCC Color Space" in SID INTERNATIONAL SYMPOSIUM.: 1130-1133, Society for Information Display. doi:10.1889/1.2433175. Retrieved on 2008-05-20. 
  3. ^ For EDTV modes (480p and 576p), even the 12-bit Deep Color data can be transported across the link using a clock well below the upper bandwidth limit of Category 1 cables.

[edit] External links

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