View source for Rec. 2100

{{short description|ITU-R recommendation}}
'''ITU-R Recommendation BT.2100''', more commonly known by the abbreviations '''Rec.&nbsp;2100''' or '''BT.2100''', introduced [[High-dynamic-range video|high-dynamic-range]] television (HDR-TV) by recommending the use of the [[perceptual quantizer]] (PQ [SMPTE ST 2084]) or [[hybrid log–gamma]] (HLG) [[Transfer functions in imaging|transfer functions]] instead of the traditional "[[Gamma correction|gamma]]" previously used for [[Standard-dynamic-range video|SDR]]-TV.<ref>{{Cite web|last=|first=|date=|title=BT.2100 : Image parameter values for high dynamic range television for use in production and international programme exchange|url=https://www.itu.int/rec/R-REC-BT.2100/en|archive-url=|archive-date=|access-date=2021-02-04|website=www.itu.int}}</ref><ref>{{Cite web|last=|first=|date=|title=BT.1886 : Reference electro-optical transfer function for flat panel displays used in HDTV studio production|url=https://www.itu.int/rec/R-REC-BT.1886/en|archive-url=|archive-date=|access-date=2021-02-04|website=www.itu.int}}</ref>
It defines various aspects of HDR-TV such as [[display resolution]] ([[HDTV]] and [[UHDTV]]), [[frame rate]], [[chroma subsampling]], [[color depth|bit depth]], [[color space]], [[Primary color|color primaries]], [[white point]], and [[Transfer functions in imaging|transfer function]].<ref name="Recommendation2100">{{cite news|url=https://www.itu.int/rec/R-REC-BT.2100|title=BT.2100 : Image parameter values for high dynamic range television for use in production and international programme exchange|date=2018-07-12|access-date=2019-01-05|publisher=International Telecommunication Union}}</ref><ref name="ITUAnnouncesHDRJuly2016">{{cite news |title=ITU announces BT.2100 HDR TV standard |publisher=Rasmus Larsen |url=http://www.flatpanelshd.com/news.php?subaction=showfull&id=1467719709 |date=2016-07-05 |access-date=2016-07-26 | work = FlatpanelsHD }}</ref> It was posted on the [[International Telecommunication Union]] (ITU) website on July 4, 2016.<ref name="Recommendation2100" /><ref name="ITUAnnouncesHDRJuly2016" /> Rec. 2100 uses a [[wide color gamut]] (WCG) which is the same as [[Rec. 2020]]'s.<ref name="ITUAnnouncesHDRJuly2016" />
== Technical details ==
=== Transfer functions ===
{{See also|Transfer functions in imaging}}
Rec.&nbsp;2100 defines two sets of HDR [[Transfer functions in imaging|transfer functions]] which are [[perceptual quantization]] (PQ) and [[hybrid log-gamma]] (HLG).<ref name="Recommendation2100" /> HLG is supported in Rec. 2100 with a nominal peak [[luminance]] of 1,000 cd/m<sup>2</sup> and a system [[gamma correction|gamma]] value that can be adjusted depending on background luminance.<ref name="Recommendation2100" /> For a reference viewing environment the peak luminance of display should be 1000 cd/m<sup>2</sup> or more for small area highlights and the black level should be 0.005 cd/m<sup>2</sup> or less.<ref name="Recommendation2100" /> The surround light should be 5 cd/m<sup>2</sup> and be neutral grey at [[standard illuminant]] [[Illuminant D65|D<sub>65</sub>]].<ref name="Recommendation2100" />
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===
{{Further|Rec. 2020#System colorimetry}}
[[File:CIExy1931_Rec_2020.svg|thumb|[[CIE 1931 color space#CIE xy chromaticity diagram and the CIE xyY color space|CIE 1931 chromaticity diagram]] showing the Rec.&nbsp;2100 (HDR-TV) [[color space]] in the triangle and the location of the [[Primary color|primary colors]]. Rec.&nbsp;2100 uses [[Illuminant D65]] for the [[white point]].]]
Rec.&nbsp;2100 uses the same [[Primary color|color primaries]] as [[Rec. 2020]] which is a [[Wide Color Gamut]].<ref name="Recommendation2100" /><ref name="ITUAnnouncesHDRJuly2016" />
{| class="wikitable"
|+RGB color space parameters<ref name="Recommendation2100" />
|-
! rowspan="2" |[[Color space]]
! colspan="2" |[[White point]]
! colspan="6" |[[Primary color]]s
|-
!x<sub>W</sub>
!y<sub>W</sub>
!x<sub>R</sub>
!y<sub>R</sub>
!x<sub>G</sub>
!y<sub>G</sub>
!x<sub>B</sub>
!y<sub>B</sub>
|-
| align="center" |ITU-R BT.2100
|0.3127
|0.3290
|0.708
|0.292
|0.170
|0.797
|0.131
|0.046
|}
===Resolution===
Rec.&nbsp;2100 specifies three resolutions of [[1080p|1920 × 1080]] ("Full HD"), [[4K resolution#CEA Ultra HD|3840 × 2160]] ("4K UHD"), and [[8K resolution#Resolutions|7680 × 4320]] ("8K UHD").<ref name="Recommendation2100" /> These resolutions have an [[aspect ratio (image)|aspect ratio]] of [[16:9]] and use square [[pixel]]s.<ref name="Recommendation2100" />
===Frame rate===
Rec.&nbsp;2100 specifies the following frame rates: 120p, 119.88p, 100p, 60p, 59.94p, 50p, 30p, 29.97p, 25p, 24p, 23.976p.<ref name=Recommendation2100/> Only [[progressive scan]] frame rates are allowed.<ref name=Recommendation2100/>
===Digital representation===
Rec.&nbsp;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]] 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.<ref name=Recommendation2100/>
===Signal formats===
Rec.&nbsp;2100 specifies the use of RGB, YCbCr, and ICtCp.<ref name="Recommendation2100" /> [[ICtCp]] provides an improved color representation that is designed for high dynamic range (HDR) and wide color gamut signals (WCG).<ref name="Recommendation2100" /><ref name="DolbyICtCpPaperApril2016Dolby">{{cite news |title=ICtCp Dolby White Paper |publisher=Dolby |url=http://www.dolby.com/us/en/technologies/dolby-vision/ICtCp-white-paper.pdf |access-date=2016-04-20}}</ref>
===Luma coefficients===
Rec.&nbsp;2100 allows for [[RGB color model|RGB]], [[YCbCr]], and [[ICtCp]] signal formats with 4:4:4, 4:2:2, and 4:2:0 [[chroma subsampling]].<ref name=Recommendation2100/> Rec.&nbsp;2100 specifies that if a [[Luma (video)|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).<ref name=Recommendation2100/>
=== Chroma sample location ===
{{Unreferenced Section|date=July 2022}}
Before Rec. BT.2020 the [[Chroma subsampling#4:2:0|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==
{{Reflist}}
==External links==
*[https://www.itu.int/rec/R-REC-BT.2100 ITU-R Recommendation BT.2100]
*[https://www.itu.int/pub/R-REP-BT.2390 ITU-R BT.2390] – A Report by [[International Telecommunication Union|ITU]] providing background information on [[High-dynamic-range video|HDR]] in general, and for the [[Perceptual Quantizer|perceptual quantization]] (PQ) and [[hybrid log–gamma]] (HLG) HDR [[signal]] parameters specified in the Rec.2100
{{Dynamic range color representation}}
{{Color space}}
[[Category:Color space]]
[[Category:Film and video technology]]
[[Category:High dynamic range]]
[[Category:ITU-R recommendations]]
[[Category:Audiovisual introductions in 2016]]
[[Category:Telecommunications-related introductions in 2016]]
[[Category:Ultra-high-definition television]]