Transfer functions in imaging: Difference between revisions

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{{Short description|Relationship between electrical signal and light}}

This article is about the [[Transfer function|transfer functionsImage]]s used inand [[Image|picturesvideo]]s anduse specific [[Video|videostransfer function]]s andto describingdescribe the relationship between [[Signal|electrical signal]], scene light and displayed light.

== Definition ==

The '''opto-electronic transfer function''' ('''OETF''') is the [[Transfer function|tranfertransfer function]] having the scene light as input and converting into the picture or video signal as output. This is typically done within a [[camera]].<ref name=":0">{{Cite web|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.2100-2-201807-I/en|access-date=2021-02-02|website=www.itu.int}}</ref>

The '''electro-optical transfer function''' ('''EOTF''') is the [[Transfer function|tranfertransfer function]] having the picture or video signal as input and converting it into the linear light output of the display.<ref name=":0" /> This is done within thea [[display device]].

The '''opto-optical transfer function''' ('''OOTF''') is the [[transfer function]] having the scene light as input and the displayed light as output. The OOTF is the result[[Function composition|composition]] of the OETF and the EOTF and is usually non-[[LinearNonlinear function (calculus)system|non-linear]].<ref name=":0" />

== List of transfer functions ==

=== [[Linear function (calculus)|Linear]] ===

* [[RAW format|Raw formats]]

A '''linear tranfer function''' describe is a [[Transfer function|tranfer function]] based on a [[Linear function (calculus)|linear function]].

*Some EOTFOETF and OETFEOTF have an initial [[Linear function (calculus)|linear]] portion followed by a non-linear part (i.e.g. [[sRGB,]] and [[Rec. 709<ref name=":1" /> and |Rec.1886709]]<ref name=":21" />).

Some EOTF and OETF have an initial linear portion followed by a non-linear part (i.e. sRGB, Rec.709<ref name=":1" /> and Rec.1886<ref name=":2" />).

=== [[Gamma correction|Gamma]] ===

* [[Rec. 601]], [[Rec. 709]] and [[Rec. 2020]]: The [[ITU-R]] '''recommendations BT.601, BT.709 and BT.2020''' describe the reference OETF of respectively [[Standard-definition television|SD-TV]],<ref name=":3" /> [[High-definition television|HD-TV]]<ref name=":1" /> and [[Ultra-high-definition television|UHD-TV]].<ref name=":4" /> They are identical OETF based on a [[gamma curve]] and used for [[Standard-dynamic-range video|SDR-TV]].<ref name=":3">{{Cite web|title=BT.601  :  Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios|url=https://www.itu.int/rec/R-REC-BT.601/en|access-date=2021-02-02|website=www.itu.int}}</ref><ref name=":1">{{Cite web|title=BT.709  :  Parameter values for the HDTV standards for production and international programme exchange|url=https://www.itu.int/rec/R-REC-BT.709/en|access-date=2021-02-02|website=www.itu.int}}</ref><ref name=":4">{{Cite web|title=BT.2020  :  Parameter values for ultra-high definition television systems for production and international programme exchange|url=https://www.itu.int/rec/R-REC-BT.2020/en|access-date=2021-02-02|website=www.itu.int}}</ref>

* [[RecBT. 1886]]: The '''ITU-R Recommendation BT.1886''' describeis the reference EOTF of [[Standard-dynamic-range video|SDR-Standard Dynamic Range TV (SDR)]].<ref name=":2">{{Cite web|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|access-date=2021-02-02|website=www.itu.int}}</ref>

* [[sRGB]]''': sRGB''' defines a transfer function based on a gamma curve and used for monitors, printers, and the [[World Wide Web|Web]]. ItsRGB is standardized as '''IEC 61966-2-1:1999'''<ref>{{Cite web|title=IEC 61966-2-1:1999 {{!}} IEC Webstore|url=https://webstore.iec.ch/publication/6169|access-date=2021-02-02|website=webstore.iec.ch}}</ref>

=== [[Logarithmic integral function|LogarithmicLogarithm]]ic ===

* '''[[S-Log]]''': Developed by [[Sony]] for [[digital camera]]s in order to increase captured [[dynamic range]]<ref>{{Cite web|title={{!}} Help Guide for Creators {{!}} What is S-Log?|url=https://helpguide.sony.net/di/pp/v1/en/contents/TP0000909108.html|access-date=2021-02-02|website=helpguide.sony.net}}</ref>

=== Other ===

* '''[[Canon Log]]''': Developed by [[Canon Inc.|Canon]] for [[digital camera]]s in order to increase captured [[dynamic range]]<ref>{{Cite web|title=Canon Log Gamma|url=https://www.canon-europe.com/cameras/eos-5d-mark-iv/canon-log-gamma/|access-date=2021-02-02|website=Canon Europe|language=en-EU}}</ref>

*Arri Log C: Developed by Arri for [[digital camera]]s in order to increase captured [[dynamic range]]<ref>{{Cite web|title=Log C|url=https://www.arri.com/en/learn-help/learn-help-camera-system/camera-workflow/image-science/log-c|access-date=2021-08-31|website=www.arri.com|language=en-US}}</ref>

=== [[High-dynamic-range television|HDR]] ===

* [[Perceptual Quantizer|Perceptual quantizer]]: '''PQ''' is a [[transfer function]] developed by [[Dolby Laboratories|Dolby]] for [[High dynamic range|HDR]] and allowing a a [[luminance]] level of up to 10,000 [[Candela per square metre|cd/m²]]. It is standardized as '''SMPTE ST 2084'''.<ref>{{Cite web|last=|first=|date=|title=An Introduction to Dolby Vision|url=https://professional.dolby.com/siteassets/pdfs/dolby-vision-whitepaper_an-introduction-to-dolby-vision_0916.pdf|url-status=live|archive-url=|archive-date=|access-date=2 February 2021|website=}}</ref>

These transfer functions have been developed to allow [[High-dynamic-range television|HDR display]]:

* [[Hybrid Log-Gamma]]: '''HLG''' is a [[transfer function]] developed by the BBC and NHK for [[High dynamic range|HDR]] and offering some [[backward compatibility]] with [[Standard-dynamic-range video|SDR]].

* [[Perceptual Quantizer|Perceptual quantizer]]: '''PQ''' is a [[transfer function]] developed by [[Dolby Laboratories|Dolby]] for [[High -dynamic-range rangevideo|HDR]] and allowing a a [[luminance]] level of up to 10,000 [[Candela per square metre|cd/m²]]. It is standardized in '''[[Rec. 2100]]'''<ref name=":5">{{Cite web|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|access-date=2021-02-23|website=www.itu.int}}</ref> and also as '''SMPTE ST 2084'''.<ref>{{Cite web|last=|first=|date=|title=An Introduction to Dolby Vision|url=https://professional.dolby.com/siteassets/pdfs/dolby-vision-whitepaper_an-introduction-to-dolby-vision_0916.pdf|url-status=live|archive-url=|archive-date=|access-date=2 February 2021|website=}}</ref>

== Transfer functions in codecs ==

* [[Hybrid log–gamma]]: '''HLG''' is a transfer function developed by [[NHK]] and [[BBC]] for [[High-dynamic-range video|HDR]] and offering some [[backward compatibility]] on [[Standard-dynamic-range video|SDR]] displays. HLG is a hybrid transfer function in which the lower half of the signal values use a [[Gamma correction|gamma curve]] and the upper half of the signal values use a [[Logarithmic growth|logarithmic curve]].<ref name="DisplayHDR2015BBC">{{cite news|author=T. Borer|author2=A. Cotton|title=A "Display Independent" High Dynamic Range Television System|publisher=[[BBC]]|url=http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP309.pdf|url-status=live|access-date=1 November 2015|archive-url=https://web.archive.org/web/20160207193353/http://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP309.pdf|archive-date=7 February 2016}}</ref><ref>{{Cite web|last=ARIB|first=Association of Radio Industries and Businesses|date=3 July 2015|title=ARIB STD-B67|url=http://www.arib.or.jp/english/html/overview/doc/2-STD-B67v1_0.pdf|url-status=live|archive-url=https://web.archive.org/web/20170329122104/http://www.arib.or.jp/english/html/overview/doc/2-STD-B67v1_0.pdf|archive-date=29 March 2017|access-date=8 August 2017}}</ref> It is standardized in '''[[Rec. 2100]]'''.<ref name=":5" />

=== HEVC ===

==References==

{{Reflist}}

== [[Category:Transfer functions in codecs ==]]

[[Category:Video]]

[[Category:Imaging]]