ITU-R recommendation BT.2020

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Diagram of the CIE 1931 color space , in which the color space of Recommendation 2020 (UHDTV) and the positions of the primary colors are drawn in with a triangle . Recommendation 2020 uses Illuminant D65 as a white point .

ITU-R recommendation BT.2020 , commonly known by the abbreviations Rec. 2020 or BT.2020 , defines various aspects of UHDTV such as screen resolution, frame rate , color subsampling , color depth and color space . It was published on 23 August 2012 on the website of the International Telecommunication Union (ITU).

Technical details

resolution

Recommendation 2020 defines two resolutions, 3840 × 2160 (" 4K ") and 7680 × 4320 (" 8K "). These resolutions have an aspect ratio of 16: 9 and use square pixels .

Frame rate

Recommendation 2020 specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p. Only full screen processes are allowed.

Digital representation

Recommendation 2020 defines a color depth of either 10 or 12 bits per sample.

With 10 bits per sample, Recommendation 2020 uses a brightness value scale in which the black point is set to code 64 and the white point to code 940. The codes 0 to 3 and 1020 to 1023 are used for the time reference. Codes 4 to 63 serve as brightness values ​​below the black point, while codes from 941 to 1019 designate brightness values ​​above the nominal peak value.

With 12 bits per sample, Recommendation 2020 uses a brightness value scale in which the black point is set to code 256 and the white point to code 3760. Codes 0 to 15 and 4080 to 4095 are used for the time reference. Codes 16 to 255 serve as brightness values ​​below the black point, while codes from 3761 to 4079 designate brightness values ​​above the nominal peak value.

System colorimetry

RGB color space parameters
Color space White point Base color
x W y W x R y R x G y G x B y B
ITU-R BT.2020 0.3127 0.3290 0.708 0.292 0.170 0.797 0.131 0.046

The color space from Recommendation 2020 (UHDTV / UHD-1 / UHD-2) can display colors that cannot be displayed with the color space from Recommendation 709 (HDTV). The RGB basic colors used by Recommendation 2020 correspond to monochrome light sources in the CIE standard color system of 1931. The wavelength of the basic colors in Recommendation 2020 are 630 nm for the basic color red, 532 nm for the green basic color and 467 nm for the blue basic color. Of the CIE color space of 1931, the color space of Recommendation 2020 covers a range of 75.8%, the digital cinema reference projector color space covers 53.6%, the Adobe RGB color space covers 52.1% and the color space of Recommendation 709 covers 35.9 % off.

During the development of the Recommendation 2020 color space, it was decided to use real possible colors instead of imaginary colors in order to enable the Recommendation 2020 color space to be mapped on a display device without additional conversion circuits. Since a larger color space increases the distances between neighboring color values, an additional bit per sample is necessary in order to achieve the same or a higher color precision as in recommendation 709.

The NHK measured the contrast sensitivity of the Recommendation 2020 color space using the Barten equation, which was previously used to determine the depth of color in digital cinema. The 11 bits per sample value in the Recommendation 2020 color space are finer than the contrast perception threshold over the entire range of the brightness scale. The NHK plans to use RGB with 12 bits per sample for its UHDTV system, Super Hi-Vision.

Luma coefficient

Recommendation 2020 allows RGB and YCbCr signal formats with 4: 4: 4, 4: 2: 2 and 4: 2: 0 color subsampling. Recommendation 2020 specifies that a possible Luma signal (Y ') uses the R'G'B' coefficients 0.2627 for red, 0.6780 for green and 0.0593 for blue.

Transfer function

Recommendation 2020 defines a non-linear transfer function that can be used for gamma correction for RGB and YCbCr. RGB can be used when the best quality is required. YCbCr can be used when the main requirement is compatibility with SDTV / HDTV operation and enables color subsampling. The Luma and Chroma components in YCbCr are calculated from gamma-corrected RGB. Recommendation 2020 also defines a linearly encoded version of YCbCr called YcCbcCrc. YcCbcCrc can be used if preserving the brightness information as true to the original as possible is a priority. The Luma and Chroma components in YcCbcCrc are calculated from linear RGB and then gamma corrected.

Recommendation 2020 with 10 bits per sample uses the same non-linear transfer function as Recommendation 709. With 12 bits per sample, the transfer function changes in Recommendation 2020, since the minimum value on the brightness scale between 0 and 1 at which the non-linear function begins is 0.0181 is higher instead of 0.018. The non-linear transfer function of Recommendation 2020 is linear close to 0 and then turns into a power function for the rest of the brightness scale :

  • E is the signal in relation to the light intensity and E 'is the resulting non-linear signal
  • α = 1.099 and β = 0.018 for a system with 10 bits per sample
  • α = 1.0993 and β = 0.0181 for a system with 12 bits per sample

Although the transfer function from Recommendation 2020 can be used for the coding, it is assumed that most productions use a reference monitor that has an image display according to the transfer function from ITU-R recommendation BT.1886, and that the reference monitor according to ITU- R recommendation BT.2035 is assessed. When producing content according to Recommendation 2020, other transmission functions such as the Dolby Perceptual Quantizer (PQ) can also be used.

Web links

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  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y BT.2020: Parameter values ​​for ultra-high definition television systems for production and international program exchange.
  2. ↑ BT.2020: Parameter values ​​for ultra-high definition television systems for production and international program exchange.
  3. ^ The international standard for Super Hi-Vision TV.
  4. ↑ 8K Ultra High Def TV Format Opens Options for TV Viewing.
  5. ↑ ITU approves NHK's Super Hi-Vision as 8K standard, sets the UHDTV ball rolling very slowly.
  6. ↑ a b c d e “Super Hi-Vision” as Next-Generation Television and Its Video Parameters. ( Memento of the original from August 2, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / informationdisplay.org
  7. ↑ a b Super Hi-Vision format. ( Memento of the original from August 13, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.nhk.or.jp
  8. ↑ a b Wide-color-gamut Super Hi-Vision System.
  9. ↑ David Wood: Deciding Tomorrow's Television parameter , European Broadcasting Union . March 8, 2012. Archived from the original on January 8, 2014. Retrieved May 2, 2013. 
  10. ↑ a b c d BT.2246-2 (2012): The present state of ultra-high definition television.
  11. ^ Super Hi-Vision Production Devices for Mobile.
  12. ↑ a b BT.709: Parameter values ​​for the HDTV standards for production and international program exchange.
  13. ↑ BT.1886: Reference electro-optical transfer function for flat panel displays used in HDTV studio production.
  14. ↑ BT.2035: A reference viewing environment for evaluation of HDTV program material or completed programs.
  15. ↑ Adam Wilt: HPA Tech Retreat 2014 - Day 4 , DV Info Net. February 20, 2014. Retrieved November 1, 2014.