Glossary

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Anomalous Trichromat(also: Anomalous Trichromacy, Colour Anomaly)

A person who has all three types of cone cells in the retina but one type has a shifted spectral sensitivity, causing altered colour perception that is less severe than dichromacy. Anomalous trichromats include protanomalous individuals (shifted L-cones, reduced red…

CIE L*a*b*(also: CIELAB, Lab Color Space, CIE Lab)

A perceptually uniform colour space defined by the International Commission on Illumination (CIE) in 1976, where the numerical distance between two colour values approximates the perceived visual difference between those colours. The three dimensions are L* (lightness, from…

CIE LUV(also: CIELUV, CIE 1976 L*u*v*)

A perceptually uniform color space defined by the International Commission on Illumination (CIE) that separates color into luminance (L*) and two chromaticity coordinates (u* and v*). Unlike RGB, which is tied to display hardware and not perceptually uniform, equal distances in…

Color Adaptive Graphics(also: Colour Adaptive Graphics)

A technique for automatically adjusting the colours in graphical content so that objects maintain similar colour contrast relative to their reference background colours, regardless of the viewing context. Unlike recolouring approaches that focus on preserving the author's…

Color Gamut(also: Colour Gamut, Gamut)

The complete range of colours that can be represented or reproduced by a particular colour space, display device, or visual system. In the context of colour vision, a trichromat's gamut encompasses the full range of colours perceivable by typical human vision, while a…

Color Perception(also: Color Vision, Chromatic Vision)

Color perception is the ability to detect, distinguish, and identify colors. Impairments in color perception range from complete color blindness (achromatopsia) to partial deficiencies in distinguishing specific color ranges, such as red-green or blue-yellow color vision…

Color Space(also: Colour Space, Color Model)

A mathematical model that describes the range of colours that can be represented as numerical values, typically using three or more coordinates. Common colour spaces include RGB (red, green, blue), used in digital displays; CMYK (cyan, magenta, yellow, key/black), used in…

Dichromat(also: Dichromacy, Dichromatic Vision)

A person with colour vision based on only two types of functional cone cells in the retina instead of the typical three, resulting in a reduced ability to distinguish certain colours. Dichromats perceive colour in a two-dimensional colour space rather than the three-dimensional…

Discrimination Ellipse(also: Discrimination Ellipsoid, MacAdam Ellipse)

A region in a color space surrounding a given color within which other colors cannot be distinguished from it by an observer. In two dimensions this region forms an ellipse; in three-dimensional color spaces it becomes an ellipsoid. The size and shape of discrimination ellipses…

Farnsworth D-15 Test(also: D-15 Color Test, Farnsworth Dichotomous Test)

The Farnsworth D-15 test is a clinical assessment used to evaluate color perception by asking a person to arrange 15 colored caps in order of hue. The pattern of errors reveals the type and severity of color vision deficiency, distinguishing between protan (red), deutan (green),…

Ishihara Test(also: Ishihara Colour Test, Ishihara Plates)

A widely used clinical screening test for red-green colour vision deficiencies, consisting of a series of circular plates made up of coloured dots arranged in a mosaic pattern. Each plate contains a number or shape formed by dots of certain colours set against a background of…

Just-Noticeable Difference(also: JND, Difference Threshold, Differential Threshold)

The smallest detectable difference between two stimuli that a person can perceive. In accessibility contexts, JND is commonly applied to color, contrast, and audio levels—determining the minimum change needed for users to distinguish between two values. For color vision, JND…

Monochromacy(also: Achromatopsia, Total Color Blindness)

The rarest and most severe form of color vision deficiency, in which an individual has complete or near-complete absence of color perception, seeing the world only in shades of gray. Monochromacy occurs when two or all three types of cone cells in the retina are absent or…

Simultaneous Color Contrast(also: Simultaneous Contrast)

A perceptual phenomenon where the appearance of a colour is influenced by the colours surrounding it, causing the same colour to look different when placed against different backgrounds. For example, a grey square appears lighter against a dark background and darker against a…

Trichromat(also: Trichromacy, Trichromatic Vision)

A person with typical colour vision based on three types of functional cone cells (L, M, and S cones) in the retina, each sensitive to different wavelengths of light corresponding roughly to long (red), medium (green), and short (blue) wavelengths. Trichromatic vision allows…

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