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. Its predecessor, Kodak Photo CD uses the same OETF as xvYCC.
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 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.
xvYCC was motivated by the fact that modern display and capture technologies often have underlying RGB primaries with significantly higher saturation than the traditional CRT displays (serving as the basis of sRGB and Rec. 709), allowing them to handle a wider color gamut. But these devices have been unable to do this without upsetting basic calibration, as all existing video storage and transmission systems are based on CRT primaries, and are hence limited to the CRT gamut.
xvYCC expands the chroma values to 1-254 while keeping the luma (Y) value range at 16-235 (though Superwhite may be supported), the same as Rec. 709. First the OETF (TransferCharacteristics 11 per H.273 as originally specified by first amendment to H.264) is expanded to allow negative RGB inputs such that:
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 (MatrixCoefficients 1 and 5).
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:
With negative primary amounts allowed, a cyan that lies outside the basic gamut of the primaries can be encoded as "green plus blue minus red". Since the 16-255 Y range is used (255 value is reserved in HDMI standard for synchronization but may be in files) and since the values of Cb and Cr are only little restricted, a lot of high saturated colors outside the 0–255 RGB space can be encoded. For example, if YCbCr is 255, 128, 128, in the case of a full level YCbCr encoding (0–255), then the corresponding sRGB is 255, 255, 255 which is the maximum encodable luminance value in this color space. But if Y=255 and Cr and/or Cb are not 128, this codes for the maximum luminance but with an added color: one primary must necessarily be above 255 and cannot be converted to sRGB. Adapted software and hardware must be used during production to not clip the video data levels that are above the sRGB space. This is almost never the case for software working with an RGB core.
The more complex example is YCbCr BT.709 values 139, 151, 24 (that is RGB -22, 182, 182). That is out-of-gamut for BT.709 but is not for sYCC and xvYCC709 and to convert those values to display gamut you would convert YCbCr to XYZ and then to display gamut.
A mechanism for signaling xvYCC support and transmitting the gamut boundary definition for xvYCC has been defined in the HDMI 1.3 Specification. No new mechanism is required for transmitting the xvYCC data itself, as it is compatible with HDMI's existing YCbCr formats, but the display needs to signal its readiness to accept the extra-gamut xvYCC values (in Colorimetry block of EDID, flags xvYCC709 and xvYCC601), and the source needs to signal the actual gamut in use in AVI InfoFrame and use gamut metadata packets to help the display to intelligently adapt extreme colors to its own gamut limitations.
This should not be confused with HDMI 1.3's other new color feature, deep color. This is a separate feature that increases the precision of brightness and color information, and is independent of xvYCC.
On January 7, 2013, Sony announced that it would release "Mastered in 4K" Blu-ray Disc titles which are sourced at 4K and encoded at 1080p. "Mastered in 4K" 1080p Blu-ray Disc titles can be played on existing Blu-ray Disc players and will support a larger color space using xvYCC.
On May 30, 2013, Eye IO announced that their encoding technology was licensed by Sony Pictures Entertainment to deliver 4K Ultra HD video with their "Sony 4K Video Unlimited Service". Eye IO encodes their video assets at 3840 x 2160 and includes support for the xvYCC color space.
The following graphics hardware support xvYCC color space when connected to a display device supporting xvYCC:
- AMD Mobility Radeon HD 4000 series and newer models
- AMD Radeon HD 5000 series and newer models
- AMD 785G, 880G and 890GX chipsets with integrated graphics
- Intel HD Graphics integrated on some CPUs (except Pentium G6950 and Celeron G1101)
- nVidia GeForce 200 series and newer models
- "HDMI 1.3 Update" (PDF). HDMI Licensing. 2006. Retrieved 2006-08-30.
- "新動画用拡張色空間 xvYCC(IEC61966-2-4)" (PDF).
- "xvYCC". Sony Global. Archived from the original on August 29, 2009. Retrieved 2009-08-13.
- Tatsuhiko Matsumoto; Yoshihide Shimpuku; Takehiro Nakatsue; Shuichi Haga; Hiroaki Eto; Yoshiyuki Akiyama & Naoya Katoh (2006). 19.2: xvYCC: A New Standard for Video Systems using Extended-Gamut YCC Color Space. SID INTERNATIONAL SYMPOSIUM. Society for Information Display. pp. 1130–1133. doi:10.1889/1.2433175.
- Naoya Katoh (2007). "New" Extended-gamut Color Space for Video Applications; xvYCC (IEC61966-2-4) (PDF). Hollywood Post Alliance. Retrieved 2009-08-13.
- "H.273: Coding-independent code points for video signal type identification". www.itu.int. Retrieved 2020-12-25.
- Richard Lawler (2013-01-07). "Sony to launch 4K digital distribution network this summer, 'mastered in 4K' Blu-ray discs". Engadget. Retrieved 2013-05-30.
- Seamus Byrne (2013-05-01). "Sony 'mastered in 4K' Blu-rays a mixed blessing". CNET. Retrieved 2013-05-30.
- "What is Mastered in 4K and does it make a difference?". Trusted Reviews. 2014-03-10. Retrieved 2020-12-24.
- "eyeIO Delivers Unprecedented Viewing Experience for Sony Pictures Content on Sony 4K UltraHD TVs". Eye IO, LLC. 2013-05-30. Retrieved 2013-06-05.
- Todd Sprangler (2013-05-30). "Sony Gears Up for 4K Ultra HD Internet Movie Service". Variety. Retrieved 2013-06-05.