xvYCC or extended-gamut YCbCr is a color space that can be used in the video electronics of television sets to support a gamut 1.8 times as large as that of the sRGB color space. xvYCC was proposed by Sony, specified by the IEC in October 2005 and published in January 2006 as IEC 61966-2-4. xvYCC extends the ITU-R BT.709 tone curve by defining over-ranged values. xvYCC-encoded video retains the same color primaries and white point as BT.709, and uses either a BT.601 or BT.709 RGB-to-YCC conversion matrix and encoding. This allows it to travel through existing digital limited range YCC data paths, and any colors within the normal gamut will be compatible. It works by allowing negative RGB inputs and expanding the output chroma. These are used to encode more saturated colors by using a greater part of the RGB values that can be encoded in the YCbCr signal compared with those used in Broadcast Safe Level. The extra-gamut colors can then be displayed by a device whose underlying technology is not limited by the standard primaries. In a paper published by Society for Information Display in 2006, the authors mapped the 769 colors in the Munsell Color Cascade (so called Michael Pointer's gamut) to the BT.709 space and to the xvYCC space. About 55% of the Munsell colors could be mapped to the sRGB gamut, but 100% of those colors map to within the xvYCC gamut. Deeper hues can be created – for example a deeper cyan by giving the opposing primary (red) a negative coefficient. The quantization range of the xvYCC601 and xvYCC709 colorimetry is always Limited Range.
Background Camera and display technology is evolving with more distinct primaries, spaced farther apart per the CIE chromaticity diagram. Displays with more separated primaries permit a larger gamut of displayable colors, however, color data needs to be available to make use of the larger gamut color space. xvYCC is an extended gamut color space that is backwards compatible with the existing BT.709 YCbCr broadcast signal by making use of otherwise unused data portions of the signal. The BT.709 YCbCr signal has unused code space, a limitation imposed for broadcasting purposes. In particular only 16-240 is used for the color Cb/Cr channels out of the 0-255 digital values available for 8 bit data encoding. xvYCC makes use of this portion of the signal to store extended gamut color data by using code values 1-15 and 241-254 in the Cb/Cr channels for gamut-extension.
Definition xvYCC expands the chroma values to 1-254 (i.e. a raw value of -0.567–0.567) while keeping the luma (Y) value range at 16-235 (though Superwhite may be supported), the same as Rec. 709. First the OETF (Transfer Characteristics 11 per H.273 as originally specified by the first amendment to H.264) is expanded to allow negative R'G'B' inputs such that:
V = { − 1.099 ( − L ) 0.45 + 0.099 L ≤ − 0.018 4.500 L − 0.018 < L < 0.018 1.099 L 0.45 − 0.099 L ≥ 0.018 {\displaystyle V={\begin{cases}-1.099(-L)^{0.45}+0.099&L\leq -0.018\\4.500L&-0.018<L<0.018\\1.099L^{0.45}-0.099&L\geq 0.018\end{cases}}}
Here 1.099 number has the value 1 + 5.5 * β = 1.099296826809442... and β has the value 0.018053968510807..., while 0.099 is 1.099 - 1. The YCC encoding matrix is unchanged, and can follow either Rec. 709 or Rec. 601 (Matrix Coefficients 1 and 5). The possible range for non-linear R’G’B’601 is between -1.0732 and 2.0835 and for R’G’B’709 is between -1.1206 and 2.1305. That is achieved when YCC values are "1, 1, any" and "254, 254, any" in B' component. xvYCC709 covers 37.19% of CIE 1976 u'v', while BT.709 only 33.24%. The last step encodes the values to a binary number (quantization). It is basically unchanged, except that a bit-depth n of more than 8 bits can be selected:
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