Rec. 2100

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ITU-R Recommendation BT.2100, more commonly known by the abbreviations Rec. 2100 or BT.2100, introduced high-dynamic-range television (HDR-TV) by recommending the use of the perceptual quantizer (PQ) or hybrid log–gamma (HLG) transfer functions instead of BT.1886 EOTF and other transfer functions previously recommended for SDR-TV.[1][2]

It defines various aspects of HDR-TV such as display resolution (HDTV and UHDTV), frame rate, chroma subsampling, bit depth, color space, and transfer function.[3][4] It was posted on the International Telecommunication Union (ITU) website on July 4, 2016.[3][4] Rec. 2100 expands on several aspects of Rec. 2020.[4]

Technical details[edit]

Transfer functions[edit]

See also: Transfer functions in imaging

Rec. 2100 defines two sets of HDR transfer functions which are perceptual quantization (PQ) and hybrid log-gamma (HLG).[3] HLG is supported in Rec. 2100 with a nominal peak luminance of 1,000 cd/m2 and a system gamma value that can be adjusted depending on background luminance.[3] For a reference viewing environment the peak luminance of display should be 1000 cd/m2 or more for small area highlights and the black level should be 0.005 cd/m2 or less.[3] The surround light should be 5 cd/m2 and be neutral grey at standard illuminant D65.[3] Avoid light falling on the screen.

Within each set, the documented transfer functions include an:

  • electro-optical transfer function (EOTF) which maps the non-linear signal value into display light
  • opto-optical transfer function (OOTF) which maps relative scene linear light to display linear light
  • opto-electronic transfer function (OETF) which maps relative scene linear light into the non-linear signal value

System colorimetry[edit]

Further information: Rec. 2020 § System colorimetry

Rec. 2100 use the same color primaries as Rec. 2020 which is a Wide Color Gamut.[3][4]

RGB color space parameters[3]
Color space White point Primary colors
xW yW xR yR xG yG xB yB
ITU-R BT.2100 0.3127 0.3290 0.708 0.292 0.170 0.797 0.131 0.046

Resolution[edit]

Rec. 2100 specifies three resolutions of 1920 × 1080 ("Full HD"), 3840 × 2160 ("4K UHD"), and 7680 × 4320 ("8K UHD").[3] These resolutions have an aspect ratio of 16:9 and use square pixels.[3]

Frame rate[edit]

Rec. 2100 specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p.[3] Only progressive scan frame rates are allowed.[3]

Digital representation[edit]

Rec. 2100 specifies a bit depth of either 10-bits per sample or 12-bits per sample, with either narrow range or full range color values.[3]

For narrow range color, 10-bits per sample use video levels where the black level is defined as 64, achromatic gray level as 512 and the nominal peak as 940 in RGB and Y encoding and 960 in Cb, Cr encoding. Codes 0–3 and 1,020–1,023 can be used for the timing reference in limited range and should be avoided.[3] 12-bits per sample use 256 as the black level, 2048 as Cb, Cr for the gray level and the nominal peak is 3760 in R', G', B', Y', I encoding and 3840 in Cb, Cr, Ct, Cp encoding.[3] Codes 0–15 and 4,080–4,095 can be used for the timing reference in limited range and should be avoided.[3]

For full range color, 10-bit levels are 0 for the black level, 512 for Cb and Cr for the grey level and 1023 for the nominal peak, and 12-bit levels are 0, 2048 and 4092 (values 4093-4095 are avoided to exclude clipping errors on 10-bit ADC/DAC circuits which have 1023 steps).[3]

Signal formats[edit]

Rec. 2100 specifies the use of RGB, YCbCr, and ICtCp.[3] ICtCp provides an improved color representation that is designed for high dynamic range (HDR) and wide color gamut signals (WCG).[3][5]

Luma coefficients[edit]

Rec. 2100 allows for RGB, YCbCr, and ICtCp signal formats with 4:4:4, 4:2:2, and 4:2:0 chroma subsampling.[3] Rec. 2100 specifies that if a luma (Y') signal is made that it use the same matrix coefficients as Rec. 2020: 0.2627 for red, 0.678 for green, and 0.0593 for blue (derived from BT.2020 primaries and white point).[3]

Chroma sample location[edit]

Before Rec. BT.2020 the chroma sample location that was in use was center left. But in H.265 (2018-02) top-left chroma siting was mandated for BT.2020-2 and BT.2100-1, that must be described in VUI (video usability information) as such. First value of VUI should be 2 for top-left chroma and 0 for center left. Blu-ray also uses top-left chroma for HDR, including for Dolby Vision.

See also[edit]

References[edit]

  1. ^ "BT.2100 : Image parameter values for high dynamic range television for use in production and international programme exchange". www.itu.int. Retrieved 2021-02-04.
  2. ^ "BT.1886 : Reference electro-optical transfer function for flat panel displays used in HDTV studio production". www.itu.int. Retrieved 2021-02-04.
  3. ^ a b c d e f g h i j k l m n o p q r s t u "BT.2100 : Image parameter values for high dynamic range television for use in production and international programme exchange". International Telecommunication Union. 2018-07-12. Retrieved 2019-01-05.
  4. ^ a b c d "ITU announces BT.2100 HDR TV standard". FlatpanelsHD. Rasmus Larsen. 2016-07-05. Retrieved 2016-07-26.
  5. ^ "ICtCp Dolby White Paper" (PDF). Dolby. Retrieved 2016-04-20.

External links[edit]

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