Color appearance model: Difference between revisions

Revision as of 16:26, 8 June 2024

Revision as of 12:27, 24 July 2024

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This section describes some of the color appearance phenomena that color appearance models try to deal with.

====[[Chromatic adaptation]]====

{{Main|Chromatic adaptation}}

Chromatic adaptation describes the ability of human color perception to abstract from the [[white point]] (or [[color temperature]]) of the illuminating light source when observing a reflective object. For the human eye, a piece of white paper looks white no matter whether the illumination is blueish or yellowish. This is the most basic and most important of all color appearance phenomena, and therefore a ''[[chromatic adaptation transform]]'' (CAT) that tries to emulate this behavior is a central component of any color appearance model.

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This section lists some of the color appearance models in use. The chromatic adaptation transforms for some of these models are listed in [[LMS color space]].

===[[CIELAB]]===

{{Main|CIELAB color space}}

In 1976, the [[International Commission on Illumination|CIE]] set out to replace the many existing, incompatible color difference models by a new, universal model for color difference. They tried to achieve this goal by creating a ''perceptually uniform'' color space (UCS), i.e. a color space where identical spatial distance between two colors equals identical amount of perceived color difference. Though they succeeded only partially, they thereby created the [[CIELAB color space|CIELAB (“L*a*b*”)]] color space which had all the necessary features to become the first color appearance model. While CIELAB is a very rudimentary color appearance model, it is one of the most widely used because it has become one of the building blocks of [[color management]] with [[ICC profile]]s. Therefore, it is basically omnipresent in digital imaging.

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After starting the evolution of color appearance models with [[#CIELAB|CIELAB]], in 1997, the CIE wanted to follow up itself with a comprehensive color appearance model. The result was CIECAM97s, which was comprehensive, but also complex and partly difficult to use. It gained widespread acceptance as a standard color appearance model until [[#CIECAM02|CIECAM02]] was published.

===[[ICtCp#In IPT|IPT]]===

{{Main|ICtCp#In IPT}}

Ebner and Fairchild addressed the issue of non-constant lines of hue in their color space dubbed ''IPT''.<ref>

{{Citation

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The IPT color appearance model excels at providing a formulation for hue where a constant hue value equals a constant perceived hue independent of the values of lightness and chroma (which is the general ideal for any color appearance model, but hard to achieve). It is therefore well-suited for [[Color management#Gamut mapping|gamut mapping]] implementations.

===[[ICtCp]]===

{{Main|ICtCp}}

ITU-R BT.2100 includes a color space called ''[[ICtCp]]'', which improves the original IPT by exploring higher dynamic

range and larger colour gamuts.<ref>

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</ref> ICtCp can be transformed into an approximately uniform color space by scaling Ct by 0.5. This transformed color space is the basis of the Rec. 2124 wide gamut color difference metric ΔE_ITP.<ref>{{cite web |title=Recommendation ITU-R BT.2124-0 Objective metric for the assessment of the potential visibility of colour differences in television |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2124-0-201901-I!!PDF-E.pdf |date=January 2019}}</ref>

===[[CIECAM02]]===

{{Main|CIECAM02}}

After the success of [[#CIECAM97s|CIECAM97s]], the CIE developed [[CIECAM02]] as its successor and published it in 2002. It performs better and is simpler at the same time. Apart from the rudimentary [[#CIELAB|CIELAB]] model, CIECAM02 comes closest to an internationally agreed upon “standard” for a (comprehensive) color appearance model.