CIECAM02

In colorimetry, CIECAM02 is the color appearance model published in 2002 by the International Commission on Illumination (CIE) Technical Committee 8-01 (Color Appearance Modelling for Color Management Systems) and the successor of CIECAM97s.^[1]

The two major parts of the model are its chromatic adaptation transform, CIECAT02, and its equations for calculating mathematical correlates for the six technically defined dimensions of color appearance: brightness (luminance), lightness, colorfulness, chroma, saturation, and hue.

Brightness is the subjective appearance of how bright an object appears given its surroundings and how it is illuminated. Lightness is the subjective appearance of how light a color appears to be. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color that appears white under similar viewing conditions. This allows for the fact that a surface of a given chroma displays increasing colorfulness as the level of illumination increases. Saturation is the colorfulness of a color relative to its own brightness. Hue is the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow, the so-called unique hues. The colors that make up an object’s appearance are best described in terms of lightness and chroma when talking about the colors that make up the object’s surface, and in terms of brightness, saturation and colorfulness when talking about the light that is emitted by or reflected off the object.

CIECAM02 takes for its input the tristimulus values of the stimulus, the tristimulus values of an adapting white point, adapting background, and surround luminance information, and whether or not observers are discounting the illuminant (color constancy is in effect). The model can be used to predict these appearance attributes or, with forward and reverse implementations for distinct viewing conditions, to compute corresponding colors.

The Windows Color System introduced in Windows Vista uses Canon's Kyuanos (キュアノス) technology for mapping image gamuts between output devices, which in turn uses CIECAM02 for color matching.^[2]

^ Fairchild, Mark D.; Luo, M. R.; Hunt, R. W. G. (August 2000). "A Revision of CIECAM97s for Practical Applications" (PDF). Color Research & Application. 25 (4). Wiley Interscience: 260–266. doi:10.1002/1520-6378(200008)25:4<260::AID-COL6>3.0.CO;2-9. Archived from the original (PDF) on 2013-09-22. Retrieved 2008-02-09. The CIECAM97s model was adopted by the CIE in 1997 for color imaging applications. It includes forward and reverse modes. Some problems in using this model were found in recent field trials. This article suggests revision to the model in two respects: (a) to make the lightness (J) zero when the Y tristimulus value is zero, under all surround conditions; (b) to modify the chromatic induction factor (Nc) from 1.10 to 0.95 for the dim surround condition. To avoid confusion, it is suggested that the revised version of the model be designated CAM97s2. The article also describes an alternative mode to achieve a more nearly exact reversibility between the forward and reverse modes.
^ “Windows Color System: The Next Generation Color Management System” Archived 2010-07-27 at the Wayback Machine. Microsoft white paper. September 13, 2005.

[cam97s-1] Fairchild, Mark D.; Luo, M. R.; Hunt, R. W. G. (August 2000). "A Revision of CIECAM97s for Practical Applications" (PDF). Color Research & Application. 25 (4). Wiley Interscience: 260–266. doi:10.1002/1520-6378(200008)25:4<260::AID-COL6>3.0.CO;2-9. Archived from the original (PDF) on 2013-09-22. Retrieved 2008-02-09. The CIECAM97s model was adopted by the CIE in 1997 for color imaging applications. It includes forward and reverse modes. Some problems in using this model were found in recent field trials. This article suggests revision to the model in two respects: (a) to make the lightness (J) zero when the Y tristimulus value is zero, under all surround conditions; (b) to modify the chromatic induction factor (Nc) from 1.10 to 0.95 for the dim surround condition. To avoid confusion, it is suggested that the revised version of the model be designated CAM97s2. The article also describes an alternative mode to achieve a more nearly exact reversibility between the forward and reverse modes.

[2] “Windows Color System: The Next Generation Color Management System” Archived 2010-07-27 at the Wayback Machine. Microsoft white paper. September 13, 2005.

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