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 The perceptual quantizer (PQ), published by SMPTE as SMPTE ST 2084, is a transfer function that allows for HDR display by replacing the gamma curve used in SDR. It is capable of representing luminance level up to 10000 cd/m2 (nits) and down ...

(PQ) 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's 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), a German science-fiction movie directed by Damir Lukacevic and starring Zana Marjanović * ''Transfer'' (1966 film), a short film * ''Transfer'' (journal), in management studies ...

instead of the traditional "

gamma Gamma (uppercase , lowercase ; ''gámma'') 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 r ...

" 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 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 resolution ...

(

HDTV High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...

and UHDTV),

frame rate Frame rate (expressed in or FPS) is the frequency (rate) at which consecutive images ( frames) are captured or displayed. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be ...

chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance. It is u ...

, 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 represen ...

, 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 ...

, 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 mathematical function that theoretically models the system's output for each possible input. They are widely used ...

. It was posted on the

International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...

(ITU) website on July 4, 2016. Rec. 2100 uses a

wide color gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given cir ...

(WCG) which is the same as

Rec. 2020 ITU-R Recommendation BT.2020, more commonly known by the abbreviations Rec. 2020 or BT.2020, defines various aspects of ultra-high-definition television (UHDTV) with standard dynamic range (SDR) and wide color gamut (WCG), including picture ...

's.

Technical details

Transfer functions

Rec. 2100 defines two sets of HDR

which are

perceptual quantization The perceptual quantizer (PQ), published by SMPTE as SMPTE ST 2084, is a transfer function that allows for HDR display by replacing the gamma curve used in SDR. It is capable of representing luminance level up to 10000 cd/m2 (nits) and down to ...

(PQ) and

hybrid log-gamma Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two diff ...

(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 with ...

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 Inter ...

D₆₅. 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

Rec. 2100 use the same color primaries as

which is a

Wide Color Gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given cir ...

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 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 image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...

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 use ...

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 Video black level is defined as the level of brightness at the darkest (black) part of a visual image or the level of brightness at which no light is emitted from a screen, resulting in a pure black screen. Video displays generally need to be cal ...

is defined as 64, achromatic gray level 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 co ...

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 addi ...

YCbCr YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-diff ...

, 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

: 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 The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union ...

providing background information on HDR in general, and for the