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 MPTE ST 2084 or

hybrid log–gamma The hybrid log–gamma (HLG) transfer function is a transfer function jointly developed by the BBC and NHK for high dynamic range (HDR) display. It is backward compatible with the transfer function of SDR (the gamma curve). It was approved as ARIB ...

(HLG)

transfer functions Transfer may refer to: Arts and media *Transfer (2010 film), ''Transfer'' (2010 film), a German science-fiction movie directed by Damir Lukacevic and starring Zana Marjanović *Transfer (1966 film), ''Transfer'' (1966 film), a short film * Transf ...

instead of the traditional "

gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...

" previously used for SDR-TV. It defines various aspects of HDR-TV such as

display resolution The display resolution or display modes of a digital television, computer monitor, or other display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resoluti ...

(

HDTV High-definition television (HDTV) describes a television or video system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since at least 1933; in more recent times, it ref ...

and

UHDTV Ultra-high-definition television (also known as Ultra HD television, Ultra HD, UHDTV, UHD and Super Hi-Vision) today includes 4K UHD and 8K UHD, which are two digital video formats with an aspect ratio of 16:9. These were first proposed by ...

frame rate Frame rate, most commonly expressed in frame/s, or FPS, is typically the frequency (rate) at which consecutive images (Film frame, frames) are captured or displayed. This definition applies to film and video cameras, computer animation, and moti ...

chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for Chrominance, chroma information than for luma (video), luma information, taking advantage of the human visual system's lower acuity for color differences t ...

, bit depth,

color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represe ...

, color primaries,

white point A white point (often referred to as reference white or target white in technical documents) is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction. Depending o ...

, and

transfer function In engineering, a transfer function (also known as system function or network function) of a system, sub-system, or component is a function (mathematics), mathematical function that mathematical model, models the system's output for each possible ...

. It was posted on the

International Telecommunication Union The International Telecommunication Union (ITU)In the other common languages of the ITU: * * is a list of specialized agencies of the United Nations, specialized agency of the United Nations responsible for many matters related to information ...

(ITU) website on July 4, 2016. Rec. 2100 uses a wide color gamut (WCG) which is the same as Rec. 2020's.

Technical details

Transfer functions

Rec. 2100 defines two sets of HDR

which are perceptual quantization (PQ) and hybrid log-gamma (HLG). HLG is supported in Rec. 2100 with a nominal peak

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...

of 1,000 cd/m² and a system

value that can be adjusted depending on background luminance. 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. The surround light should be 5 cd/m² and be neutral grey at

standard illuminant A standard illuminant is a theoretical source of visible light with a spectral power distribution that is published. Standard illuminants provide a basis for comparing images or colors recorded under different lighting. CIE illuminants The Inte ...

D₆₅. 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

Rec. 2100 uses the same color primaries as Rec. 2020 which is a Wide Color Gamut.

Resolution

Rec. 2100 specifies three resolutions of 1920 × 1080 ("Full HD"), 3840 × 2160 ("4K UHD"), and 7680 × 4320 ("8K UHD"). These resolutions have an

aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...

of 16:9 and use square

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

Frame rate

Rec. 2100 specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p. Only

progressive scan Progressive scanning (alternatively referred to as noninterlaced scanning) is a format of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to interlaced video us ...

frame rates are allowed.

Digital representation

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. A future-use and intermediate linear RGB format using IEEE 16 bit floating point representation for each channel is also specified. For narrow range color, 10-bit per sample signals use video levels where the black level is defined as 64, achromatic

gray level In digital photography, computer-generated imagery, and colorimetry, a greyscale (more common in Commonwealth English) or grayscale (more common in American English) image is one in which the value of each pixel is a single sample represent ...

as 512 and the nominal peak as 940 in RGB, Y, and I encoding and 960 in Cb/Cr, and Ct/Cp component encoding. 12-bit per sample signals define 256 as the black level, 2048 as the gray level and the nominal peak is 3760 in RGB, Y, and I component encoding and 3840 in Cb/Cr, and Ct/Cp component encoding. Narrow range signals may extend below black or above peak white (super-black and super-white respectively), but must always be clipped to the signal range of 4-1019 for 10-bit signals or 16-4079 for 12-bit signals.

Signal formats

Rec. 2100 specifies the use of RGB, YCbCr, and ICtCp.

ICtCp ''ICTCP'', ''ICtCp'', or ''ITP'' is a color representation format specified in the Rec. ITU-R BT.2100 standard that is used as a part of the color image pipeline in video and digital photography systems for high dynamic range (HDR) and wide c ...

provides an improved color representation that is designed for high dynamic range (HDR) and wide color gamut signals (WCG).

Luma coefficients

Rec. 2100 allows for

RGB The RGB color model is an additive color model in which the red, green, and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three ...

YCbCr YCbCr, Y′CbCr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in digital video and digital photography, photography systems. Like YPbPr, YPBPR, it is based on RGB primaries; the two ...

, and

signal formats with 4:4:4, 4:2:2, and 4:2:0

. 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).

Chroma sample location

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.

References

External links

ITU-R Recommendation BT.2100ITU-R BT.2390
– A Report by ITU providing background information on HDR in general, and for the perceptual quantization (PQ) and

(HLG) HDR

signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

parameters specified in the Rec.2100 {{Color space Color space Film and video technology High dynamic range ITU-R recommendations Audiovisual introductions in 2016 Telecommunications-related introductions in 2016 Ultra-high-definition television