Editing Gamma correction (section)

==Explanation==
Gamma encoding of images is used to optimize the usage of bits when encoding an image, or bandwidth used to transport an image, by taking advantage of the non-linear manner in which humans perceive light and color.<ref name=poynton/> The human perception of brightness ([[lightness]]), under common illumination conditions (neither pitch black nor blindingly bright), follows an approximate [[power function]] (which has no relation to the [[gamma function]]), with greater sensitivity to relative differences between darker tones than between lighter tones, consistent with the [[Stevens power law]] for brightness perception. If images are not gamma-encoded, they allocate too many bits or too much bandwidth to highlights that humans cannot differentiate, and too few bits or too little bandwidth to shadow values that humans are sensitive to and would require more bits/bandwidth to maintain the same visual quality.<ref>{{cite web |url=http://www.w3.org/TR/PNG-GammaAppendix.html |title=PNG Specification 13. Appendix: Gamma Tutorial |publisher=W3C |date=1996-10-01 |access-date=2018-12-03 |quote=What is gamma correction? }}</ref><ref name=poynton/><ref name=FQAGamma>[http://www.poynton.com/notes/color/GammaFQA.html Charles Poynton (2010). Frequently Questioned Answers about Gamma.]</ref> Gamma encoding of [[floating-point]] images is not required (and may be counterproductive), because the floating-point format already provides a piecewise linear approximation of a logarithmic curve.<ref>{{cite book|author1=Erik Reinhard |author2=Wolfgang Heidrich |author3=Paul Debevec |author4=Sumanta Pattanaik |author5=Greg Ward |author6=Karol Myszkowski | title = High Dynamic Range Imaging: Acquisition, Display, and Image-Based Lighting | year = 2010 | publisher = Morgan Kaufmann | isbn = 9780080957111 | page = 82 | url = https://books.google.com/books?id=w1i_1kejoYcC&pg=PA82}}</ref>

Although gamma encoding was developed originally to compensate for the brightness characteristics of [[cathode-ray tube]] (CRT) displays, that is not its main purpose or advantage in modern systems. In CRT displays, the light intensity varies nonlinearly with the electron-gun voltage. Altering the input signal by gamma compression can cancel this nonlinearity, such that the output picture has the intended luminance. However, the gamma characteristics of the display device do not play a factor in the gamma encoding of images and video. They need gamma encoding to maximize the visual quality of the signal, regardless of the gamma characteristics of the display device.<ref name=poynton/><ref name=FQAGamma/> The similarity of CRT physics to the inverse of gamma encoding needed for video transmission was a combination of coincidence and engineering, which simplified the electronics in early television sets.<ref>{{cite web |last=McKesson|first=Jason L. |title=Chapter 12. Dynamic Range – Linearity and Gamma |url=http://www.arcsynthesis.org/gltut/Illumination/Tut12%20Monitors%20and%20Gamma.html |archive-url=https://web.archive.org/web/20130718042406/http://www.arcsynthesis.org/gltut/Illumination/Tut12%20Monitors%20and%20Gamma.html |archive-date=18 July 2013 |work=Learning Modern 3D Graphics Programming |access-date=11 July 2013}}</ref>

Photographic film has a much greater ability to record fine differences in shade than can be reproduced on [[photographic paper]]. Similarly, most video screens are not capable of displaying the range of brightnesses (dynamic range) that can be captured by typical electronic cameras.<ref>
{{cite book|author=Peter Hodges|url=https://books.google.com/books?id=Fmd0lbD32R0C&pg=PA174|title=An introduction to video and audio measurement|publisher=Elsevier|year=2004|isbn=978-0-240-80621-1|edition=3rd|page=174}}</ref>
For this reason, considerable artistic effort is invested in choosing the reduced form in which the original image should be presented. The gamma correction, or contrast selection, is part of the photographic repertoire used to adjust the reproduced image.

Analogously, digital cameras record light using electronic sensors that usually respond linearly. In the process of rendering linear raw data to conventional [[RGB color model|RGB]] data (e.g. for storage into [[JPEG]] image format), color space transformations and rendering transformations will be performed. In particular, almost all standard [[RGB color space]]s and file formats use a non-linear encoding (a gamma compression) of the intended intensities of the [[primary color]]s of the photographic reproduction. In addition, the intended reproduction is almost always nonlinearly related to the measured scene intensities, via a [[tone reproduction]] nonlinearity.