Color appearance model: Difference between revisions

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{{further|Color perception}}

[[Color]] originates in the mind of the observer; “objectively”“subjectively”, there is only the [[spectral power distribution]] of the light that meets the eye. In this sense, ''any'' color perception is subjective. However, successful attempts have been made to map the spectral power distribution of light to human sensory response in a quantifiable way. In 1931, using [[Psychophysics|psychophysical]] measurements, the [[International Commission on Illumination|International Commission on Illumination (CIE)]] created the [[CIE 1931 color space|XYZ color space]]<ref>“XYZ” refers to a color ''model'' and a color ''space'' at the same time, because the XYZ color space is the only color space that uses the XYZ color model. This differs from e.g. the RGB color model, which many color spaces (such as [[sRGB]] or [[Adobe RGB color space|Adobe RGB (1998)]]) use.</ref> which successfully models human color vision on this basic sensory level.

However, the XYZ color model presupposes specific viewing conditions (such as the retinal locus of stimulation, the luminance level of the light that meets the eye, the background behind the observed object, and the luminance level of the surrounding light). Only if all these conditions stay constant will two identical stimuli with thereby identical XYZ [[CIE 1931 color space#Tristimulus values|tristimulus]] values create an identical '''color appearance''' for a human observer. If some conditions change in one case, two identical stimuli with thereby identical XYZ tristimulus values will create {{em|different}} color appearances (and vice versa: two different stimuli with thereby different XYZ tristimulus values might create an {{em|identical}} color appearance).

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Several effects change the perception of hue by a human observer:

* '''[[Bezold–Brücke shift|Bezold–Brücke hue shift]]:''' The hue of monochromatica lightstimulus of constant chromaticity changes with [[luminance]].

* '''[[Abney effect]]:''' The hue of monochromatic light changes with the addition of white light (which would be expected color-neutral).

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===CIECAM97s===

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.

===IPT===

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===OKLab===

{{Main|Oklab color space}}

A 2020 UCS designed for normal dynamic range color. Same structure as CIELAB, but fitted with improved data (CAM16 output for lightness and chroma; IPT data for hue). Meant to be easy to implement and use (especially from sRGB), just like CIELAB and IPT were, but with improvements to uniformity.<ref>{{cite web |last1=Ottosson |first1=Björn |title=A perceptual color space for image processing |date=23 December 2020 |url=https://bottosson.github.io/posts/oklab/ |language=en}}</ref>

As of September 2023, it is part of the [[CSS color]] level 4 draft<ref>{{cite web |title=CSS Color Module Level 4 |url=https://www.w3.org/TR/css-color-4/#resolving-oklab-oklch-values |website=www.w3.org}}</ref> and it is supported by recent versions of all major browsers.<ref>{{cite web |title=oklab() (Oklab color model) |url=https://caniuse.com/mdn-css_types_color_oklab |website=Can I use... |access-date=27 September 2023}}</ref>