 CIE 1931 chromaticity diagram showing the Rec. 2020 (UHDTV)color space in the triangle and the location of theprimary colors. Rec. 2020 usesIlluminant D65 for thewhite point. | |
| Status | Approved |
|---|---|
| First published | August 23, 2012; 12 years ago (2012-08-23)[1] |
| Latest version | BT.2020-2 October 14, 2015; 9 years ago (2015-10-14)[2] |
| Authors | ITU-R |
| Base standards | Rec. 2020, BT.2020 |
| Domain | Digital image processing |
| Website | www |
ITU-R Recommendation BT.2020, more commonly known by the abbreviationsRec. 2020 orBT.2020, defines various aspects ofultra-high-definition television (UHDTV) withstandard dynamic range (SDR) andwide color gamut (WCG), includingpicture resolutions,frame rates withprogressive scan,bit depths,color primaries,RGB andluma-chroma color representations,chroma subsamplings, and anopto-electronic transfer function.[2] The first version of Rec. 2020 was posted on theInternational Telecommunication Union (ITU) website on August 23, 2012, and two further editions have been published since then.[2][1][3][4][5]
Rec. 2020 is extended forhigh-dynamic-range (HDR) byRec. 2100, which uses the same color primaries as Rec. 2020.
Rec. 2020 defines two standard image formats of3840 × 2160 ("4K") and7680 × 4320 ("8K").[2] These both have anaspect ratio of16:9 and use squarepixels.[2]
Rec. 2020 specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p.[2] Onlyprogressive scan frame rates are allowed.[2]
Rec. 2020 defines a bit depth of either 10 bits per sample or 12 bits per sample.[2]
10 bits per sample Rec. 2020 uses video levels where theblack level is defined as code 64 and the nominal peak is defined as code 940. Codes 0–3 and 1,020–1,023 are used for the timing reference. Codes 4 through 63 provide video data below the black level while codes 941 through 1,019 provide video data above the nominal peak.[2]
12 bits per sample Rec. 2020 uses video levels where the black level is defined as code 256 and the nominal peak is defined as code 3760. Codes 0–15 and 4,080–4,095 are used for the timing reference. Codes 16 through 255 provide video data below the black level while codes 3,761 through 4,079 provide video data above the nominal peak.[2]
| Color space | White point | Primaries | ||||||
|---|---|---|---|---|---|---|---|---|
| xW | yW | xR | yR | xG | yG | xB | yB | |
| ITU-R BT.2020 | 0.3127 | 0.3290 | 0.708 | 0.292 | 0.170 | 0.797 | 0.131 | 0.046 |
The Rec. 2020 (UHDTV/UHD-1/UHD-2) color space can reproduce colors that cannot be shown with theRec. 709 (HDTV) color space.[6][7] The RGB primaries used by Rec. 2020 are equivalent to monochromatic light sources on theCIE 1931 spectral locus.[7][8][9] Thewavelength of the Rec. 2020primary colors is 630 nm for the red primary color, 532 nm for the green primary color, and 467 nm for the blue primary color.[8][10][11] In coverage of theCIE 1931 color space, the Rec. 2020 color space covers 75.8%, theDCI-P3 digital cinema color space covers 53.6%, theAdobe RGB color space covers 52.1%, and the Rec. 709 color space covers 35.9%.[6]
During the development of the Rec. 2020 color space it was decided that it would use real colors, instead ofimaginary colors, so that it would be possible to show the Rec. 2020 color space on a display without the need for conversion circuitry.[12] Since a larger color space increases the difference between colors, an increase of 1 bit per sample is needed for Rec. 2020 to equal or exceed the color precision of Rec. 709.[12]
TheNHK measuredcontrast sensitivity for the Rec. 2020 color space usingBarten's equation which had previously been used to determine the bit depth for digital cinema.[13][6] 11 bits per sample for the Rec. 2020 color space is below the visual modulation threshold, the ability to discern a one-value difference inluminance, for the entire luminance range.[6] The NHK is planning for their UHDTV system,Super Hi-Vision, to use 12 bits per sampleRGB.[6][14]
Rec. 2020 defines anonlineartransfer function forgamma correction that is the same nonlinear transfer function that is used byRec. 709, except that its parameters are (for 12 bit only) given with higher precision:[2][15]
The standard says that for practical purposes, the following values ofα andβ can be used:
While the Rec. 2020 transfer function can be used for encoding, it is expected that most productions will use a reference monitor that has an appearance of using equivalent ofgamma 2.4 transfer function as defined inITU-R BT.1886 and that the reference monitor will be evaluated under viewing conditions as defined in Rec. ITU-R BT.2035.[2][16][17]
Rec. 2020 allows forRGB and luma-chroma signal formats with 4:4:4 full-resolution sampling and luma-chroma signal formats with 4:2:2 and 4:2:0chroma subsampling.[2] It supports two types of luma-chroma signals, calledYCbCr and YcCbcCrc.
YCbCr may be used when the top priority is compatibility with existingSDTV andHDTV operating practices.[2][12] Theluma (Y′) signal for YCbCr is calculated as theweighted average Y′ = KR⋅R′ + KG⋅G′ + KB⋅B′, using the gamma-corrected RGB values (denoted R′G′B′) and the weighting coefficients KR = 0.2627, KG = 1−KR−KB = 0.678, and KB = 0.0593.[2] As insimilar schemes, the chroma components in YCbCr are calculated as C′B = 0.5⋅(B′−Y′)/(1−KB) = (B'−Y′)/1.8814 and C′R = 0.5⋅(R′−Y′)/(1−KR) = (R′−Y′)/1.4746, and for digital representation the Y′, C′B, and C′R signals are scaled, offset by constants, and rounded to integers.
The YcCbcCrc scheme is a "constant luminance" luma-chroma representation.[2] YcCbcCrc may be used when the top priority is the most accurate retention of luminance information.[2] The luma component in YcCbcCrc is calculated using the same coefficient values as for YCbCr, but it is calculated from linear RGB and then gamma corrected, rather than being calculated from gamma-corrected R′G′B′ and is done as follows: Y′ = (KR⋅R + KG⋅G + KB⋅B)′.[12] The chroma components in YcCbcCrc are calculated from the Y′, B′, and R′ signals with equations that depend on the range of values of B′−Y′ and R′−Y′.
Just like standard definition content that usesSMPTE C orNTSC 1953, BT.2020 primaries should be color managed to primaries of display. That is different from changing YCbCr matrix. HD content is color managed to BT.709 primaries on linear values. BT.2020 and BT.2100 are usually color managed to P3-D65.[18][19][20] The reference color bars for BT.2020 areARIB STD-B66.[21]
HDMI 2.0 supports the Rec. 2020 color space.[22] HDMI 2.0 can transmit 12 bits per sample RGB at a resolution of 2160p and a frame rate of 24/25/30 fps or it can transmit 12 bits per sample 4:2:2/4:2:0 YCbCr at a resolution of 2160p and a frame rate of 50/60 fps.[22]
The Rec. 2020 color space is supported byH.264/MPEG-4 AVC and H.265/High Efficiency Video Coding (HEVC).[23][24][25] The Main 10 profile in HEVC was added based on proposal JCTVC-K0109 which proposed that a 10-bit profile be added to HEVC for consumer applications.[26] The proposal stated that this was to allow for improved video quality and to support the Rec. 2020 color space that will be used by UHDTV.[26]
On September 11, 2013, ViXS Systems announced the XCode 6400 SoC which supports4K resolution at 60 fps, the Main 10 profile of HEVC, and the Rec. 2020 color space.[27]
On May 22, 2014,Nanosys announced that using aquantum dot enhancement film (QDEF) a current LCD TV was modified so that it could cover 91% of the Rec. 2020 color space.[28] Nanosys engineers believe that with improved LCD color filters it is possible to make a LCD that covers 97% of the Rec. 2020 color space.[28]
On September 4, 2014,Canon Inc. released a firmware upgrade that added support for the Rec. 2020 color space to their EOS C500 and EOS C500 PL camera models and their DP-V3010 4K display.[29][30]
On September 5, 2014, theBlu-ray Disc Association revealed that the future 4KBlu-ray Disc format will support 4K UHD (3840 x 2160 resolution) video at frame rates up to 60 fps.[31] The standard will encode videos under theHigh Efficiency Video Coding standard.[31] 4K Blu-ray Discs support both a higher color precision by increasing thecolor depth to 10 bits per color, and a greater color gamut by using the Rec. 2020 color space.[31] The 4K Blu-ray specification allows for three disc sizes: 50 gb, 66 gb and 100 gb. Depending on the disc size and physical configuration, the data rate can reach up to 128 Mbit/s.[31] The firstUltra HD Blu-ray titles were officially released from four studios on March 1, 2016.[32]
On November 6, 2014,Google added support for the Rec. 2020 color space toVP9.[33]
On November 7, 2014, DivX developers announced that DivX265 version 1.4.21 had added support for the Main 10 profile of HEVC and the Rec. 2020 color space.[34]
On December 22, 2014,Avid Technology released an update forMedia Composer that added support for 4K resolution, the Rec. 2020 color space, and a bit rate of up to 3,730 Mbit/s with theDNxHD codec.[35][36]
On January 6, 2015, the MHL Consortium announced the release of thesuperMHL specification which will support8K resolution at 120 fps, 48-bit video, the Rec. 2020 color space, high dynamic range support, a 32-pin reversible superMHL connector, and power charging of up to 40 watts.[37][38][39]
On January 7, 2015,Ateme added support for the Rec. 2020 color space to their TITAN File video platform.[40]
On March 18, 2015,Arri announced the SXT line ofArri Alexa cameras which will supportApple ProRes recording at 4K resolution and the Rec. 2020 color space.[41][42]
On April 8, 2015, Canon Inc. announced the DP-V2410 4K display and EOS C300 Mark II camera with support for the Rec. 2020 color space.[43][44]
On May 26, 2015, the NHK announced a 4K LCD with alaser diode backlight that covers 98% of the Rec. 2020 color space. Using a laser allows for generating almost monochromatic light.[45][46] The NHK stated that at the time it was announced this 4K LCD has the widest color gamut of any display in the world.[47]
On June 17, 2015, Digital Projection International presented a 4K LED projector with support for the Rec. 2020 color space.[48]
On January 4, 2016, the UHD Alliance announced their specifications for Ultra HD Premium which includes support for the Rec. 2020 color space.[49]
On January 27, 2016, VESA announced thatDisplayPort version 1.4 will support the Rec. 2020 color space.[50]
On April 17, 2016,Sony presented a 55 in (140 cm) 4K OLED display with the support of Rec. 2020 color space.[51]
On April 18, 2016, theUltra HD Forum announced industry guidelines for UHD Phase A which includes support for the Rec. 2020 color space.[52][53]
AtSID display week 2017,AUO displayed a 5" foldable 720p HD AMOLED display able to display 95% of the Rec. 2020 colorspace. Although 720p is not specified by Rec. 2020, the color space coverage is of note.
The Ultra HD Forum guidelines forUHD Phase A include support for SDR formats with 10 bits of color bit depth based on both Rec. 709 and Rec. 2020 color gamuts and also both the HDR10 and HLG formats of Rec. 2100, which are supposed to start by 2017.[52]
AtSID display week 2018, various companies showcased displays that are able to cover over 90% of the Rec. 2020 color space.JDI showcased an improvement of their 17.3" LCD 8k broadcast monitor that is powered by an RGB laser backlight system. This allows the display to reproduce 97% of the Rec. 2020 color space.
Rec. 2020 colors are supported inCSS Color Level 4 onSafari since 2022 (version 15.1) andGoogle Chrome since 2023 (version 111) browsers.[54][55]
| sRGB | Rec. 2020 | |
|---|---|---|
| Red | ||
| Green | ||
| Blue |
Rec. 2100 is an ITU-R Recommendation released in July 2016 that defineshigh dynamic range (HDR) formats for both HDTV 1080p and 4K/8K UHDTV resolutions.[56] These formats use the same color primaries as Rec. 2020, but with different transfer functions for HDR use.Rec. 2100 does not support the YcCbcCrc scheme of Rec. 2020.
| CAM | |
|---|---|
| CIE | |
| RGB | |
| Y′UV | |
| Other | |
| Color systems and standards | |
For the vision capacities of organisms or machines, see  Color vision. | |