"a", n - Redness-greenness coordinate in certain transformed color spaces (Hunter L,a,b or CIELAB), generally used as the difference in "a" between a specimen and a standard reference color. If "a"  is positive, there is more redness than greenness; if "a" is negative,there is more greenness than redness. It is normally used with b as part of the chromaticity or chromaticity color difference.

absolute data, n  - color measurement data presented without comparison of the sample to a standard or calculated color difference.

absorption, n - (1) penetration of one substance into the mass of another. (2) decrease in directional transmittance of incident radiation (such as light), resulting in a modification or conversion of the absorbed energy, into heat, for example. Light incident on a specimen may be partially reflected, partially transmitted, or partially absorbed.

absorption tinting strength, n – relative change in the absorption properties of a standard white material when a specified amount of an absorbing colorant, black or chromatic is added to it.

accuracy, n – the closeness of agreement between a test result and an accepted reference value (often used as a color instrument specification).

achromatic, adj – (1) for primary light sources, the computed chromaticity of the equal-energy spectrum.        (2) for surface colors, the color of a whitish light, serving as the illuminant, to which adaptation has taken place in the visual system of the observer. (3) perceived as having no hue, that is, as white, gray, or black.

additive color mixture, n – superposition or other nondestructive combination of lights of different perceived colors.

angle of illumination, n – angle between the specimen normal and the illuminator axis.

angle of view, n – angle between the normal to the surface of the specimen and the axis of the receiver.

aperture, n - the measurement opening in a typical reflection color instrument. The size of the aperture determines the size and type of sample that can be measured.

appearance, n -- manifestation of the nature of objects and materials through visual attributes such as size, shape, color, texture, glossiness, transparency, opacity, etc.

artificial daylight, n -- term loosely applied to light sources, frequently equipped with filters, which are claimed to reproduce the color and spectral distribution of daylight. A more specific definition of the light source is to be preferred.

attributes of color, n – (1) for the object mode of appearance, hue, lightness, and saturation. In the Munsell system, Munsell Hue, Munsell Value, and Munsell Chroma. (2) for the illuminant or aperture mode, hue, brightness, and saturation.

averaging, vt – a method of color measurement that allows you to average several measurements into one color measurement. Averaging is recommended when measuring standards or samples with surface variation. Usually the sample is turned 90° between measurements.

"b", n -- yellowness-blueness coordinate in certain color spaces (Hunter L,a,b & CIELAB), generally used as the difference in "b" between a specimen and a standard reference color, normally used with "a" or "a" as part of the chromaticity difference. Generally, if "b" is positive, there is more yellowness than blueness; if "b" is negative, there is more blueness than yellowness.

basic color terms, n – a group of 11 color names found in anthropological surveys to be in wide use in fully developed languages: white, black, red, green, yellow, blue, brown, gray, orange, purple, pink.

Beer’s law, n – the absorbence of a homogeneous sample containing an absorbing substance is directly proportional to the concentration of the absorbing substance, often used in mixture prediction of transparent materials.

black, n -- ideally, the complete absorption of incident light; the absence of any reflection. In the practical sense, any color that is close to this ideal in a relative viewing situation, i.e., a color of very low saturation and of low luminance.

brightness, n – (1) aspect of visual perception whereby an area appears to emit more or less light;  (2) of an object color, combination of lightness and saturation; (3) in the textile industry, perceived as saturated, vivid, deep, or clean. (color);  (4) of paper, reflectance of an infinitely thick specimen (reflectivity) measured for blue light with a centroid wavelength of 457 nm under specified spectral and geometric conditions of measurement. (5) dyer’s, the color quality, combining lightness and saturation that would be decreased by adding black, gray, or a complementary color to a chromatic dye.

bronzy color (or bronzing), n – a metallic coloration observed when viewing the light reflected at angles near the angle of specular reflection, the color usually being quite different from that observed for other directions (i.e., paint samples).

C or Delta c, n -- abbreviations for chromaticity or chromaticity difference, respectively.

calibrate, vt – to find and eliminate systematic errors of an instrument scale or method of instrument by use of material standards and techniques traceable to an authorized national or international measurement system.

characterize, vt – to specify the parameters or performance of an instrument, method of measurement, or material absorption and scatter.

chroma, n – (1) attribute of color used to indicate the degree of departure of the color from a gray of the same lightness. (2) C*, (in the CIE 1976 L*, a*, b* or L*, u*, v* system) the quantity C*_ab = (a*² + b*²)^1/2 or C*_uv = (u*² + v*²)^1/2.  (3) attribute of a visual perception, produced by an object color that permits a judgment to be made of the amount of pure chromatic color present, irrespective of the amount of achromatic color.

chromatic, adj – perceived as having a hue; not white, gray, or black. (opposite of achromatic)

chromaticity, n -- dimensions of a color stimulus expressed in terms of hue and saturation, or redness-greenness and yellowness-blueness, excluding the luminous intensity; generally expressed as a point in a plane of constant luminance. Syn: chromaticness.

chromaticity coordinates, CIE, n -- the ratios of each of the three tristimulus values X, Y and Z in relation to the sum of the three; designated as x, y and z, respectively. They are sometimes referred to as the trichromatic coefficients. When written without subscripts, they are assumed to have been calculated for Illuminant C and the 2° (1931) Standard Observer unless specified otherwise. If they have been obtained for other illuminants or observers, a subscript describing the observer or illuminant should be used. For example, x₁₀ and y₁₀ are chromaticity coordinates for the 10° observer and Illuminant C.

chromaticity diagram, CIE, n -- a two-dimensional graph of the chromaticity coordinates, x as the abscissa and y as the ordinate, which shows the spectrum locus (chromaticity coordinates of monochromatic light, 380-770 nm). It has many useful properties for comparing colors of both luminous (light emitting) and nonluminous (reflective) materials.

CIE, n – the abbreviation for the French title of the International Commission on Illumination, Commission Internationale de l’Eclairage.

CIE 1931 standard observer, n – ideal colorimetric observer with color matching functions x^-(y), y^-(y), z^-(y) corresponding to a field of view subtending a 2º angle on the retina; commonly called the "2º standard observer."

CIE 1964 supplementary standard observer, n – ideal colorimetric observer with color matching functions x^-₁₀(y), y^-₁₀(y), z^-₁₀(y) corresponding to a field of view subtending a 10º angle on the retina; commonly called the "10º standard observer."

CIELAB color difference, n – color difference calculated by using the CIE 1976 L* a* b* opponent-color scales (also referred to as CIELAB), based on applying a cube-root transformation to CIE 1931 tristimulus values X, Y, Z or CIE 1964 tristimulus values X₁₀, Y₁₀, Z₁₀.

clarity, n – the characteristic of a transparent body whereby distinct high-contrast images or high-contrast objects (separated by some distance from the body) are observable through the body.

cmc (l:c) color difference, n – color difference calculated by use of the formula developed by the Colour Measurement Committee of the Society of Dyers and Colourists of Great Britain.

Discussion – Based on the lightness, hue, chroma version of CIELAB, it incorporates chroma and hue-angle correction terms for improved visual spacing and variable weighting factors for lightness (l) and chroma (c) relative to hue for improved correlation depending on type of judgment (acceptability, perceptibility) and application (textiles, others). CMC reports the equivalent of D E as a weighted function of the ratio of L:Ch as Performance Factor=PF.

color, n – (1) of an object, aspect of object appearance distinct from form, shape, size, position, or gloss that depends upon the spectral composition of the incident light, the spectral reflectance of transmittance of the object, and the spectral response of the observer, as well as the illuminating and viewing geometry.  (2) perceived, attribute of visual perception that can be described by color names such as white, gray, black, yellow, brown, vivid red, deep reddish purple, or by combinations of such names.  (3) psychophysical, characteristics of a color stimulus (that is, light producing a sensation of color) denoted by a colorimetric specification with three values, such as tristimulus values.

colorant, n – dye, pigment, or other agent used to impart a color to a material.

color atlas, n – a collection of color samples arranged according to a color order system (such as Munsell, NCS, DIN).

color constancy, n – the general tendency of the colors of an object to remain constant when the color of the illumination is changed.

color difference, n – (1) perceived, the magnitude and character of the difference between two colors described by such terms as redder, bluer, lighter, darker, grayer, or cleaner.  (2) computed, the magnitude and direction of the difference between two psychophysical color stimuli and their components computed from tristimulus values, or chromaticity coordinates and luminance factor, by means of a specified set of color-difference equations.

color-difference units, n – units of size of the color differences calculated according to various equations. Such color differences cannot be accurately converted between different equations by the use of average factors.

colorimeter tristimulus, n – instrument that measures psychophysical color, in terms of tristimulus values, by the use of filters to convert the relative spectral power distribution of the illuminator to that of a standard illuminant, and to convert the relative spectral responsively of the receiver to the responsivities prescribed for a standard observer. See spectrocolorimeter.

colorimetry, n – the science of color measurement.

colorist, n -- a person skilled in the art of color matching (colorant formulation) and knowledgeable concerning the behavior of colorants in a particular material; a tinter (q.v.) (in the American usage) or a shader.

color match, n – (1) condition existing when colors match within a specified or agreed tolerance. Sometimes called commercial color match. (2) condition existing when colors are indistinguishable; a normal observer is usually implied. Sometimes called an exact color match.

color matching, n – procedure for providing, by selection, formulation, adjustment, or other means, a trial color that is indistinguishable from, or within specified tolerances of, a specified standard color under specified conditions.

color-matching functions, n -- the amounts, in any trichromatic system, of the three-reference color stimuli needed to match by an additive mixture monochromatic components of an equal energy spectrum.

color measurement, n -- physical measurement of light radiated, transmitted, or reflected by a specimen under specified conditions and mathematically transformed into standardized colorimetric terms that can be correlated with visual evaluations of color relative to one another. Although the term "color measurement" is normally used, color itself cannot be measured.

color order systems, n – a rational method or plan of ordering and specifying all object colors, or all within a limited domain, by means of a set of material standards selected and displayed so as to represent adequately the whole set of object colors under consideration.

color perception, n – subjective impression of color, as modified by the conditions of observation and by mental interpretation of the stimulus object.

color space, n – a geometric space, usually of three dimensions, in which colors are arranged systematically.

color specification, n – notation or set of three color-scale values used to designate a color in a specified color system. Practical color specifications may include color tolerances as well as target color designation, measuring instrument, instrument settings, measurement procedures and sample preparation procedures.

color stimulus, n – a radiant flux capable of producing a color perception.

color temperature, n – of a light source, the temperature, usually expressed in kelvins, of a full radiator (perfect, theoretical black substance that when heated would not affect the "color" of the light emitted) which emits light of the same chromaticity as the source. For example average daylight color temperature is often expressed as D65, for 6,500 degrees Kevin.

color tolerance, n – the permissible color difference between sample and specified color (Standard).

color tolerance set, n – a group of colored standards, usually seven painted chips, arranged on a single card, one exhibiting a desired color, and two each exhibiting the limits of the permissible range of color variation in each of the color attributes. Normally the set is arranged as the acceptable limits in lightness to darkness, redness to greenness, yellowness to blueness.

contrast, n – objective, the degree of dissimilarity of a measured quantity such as luminance of two areas, expressed as a number computed by a specified formula.

contrast ratio, n – see, contrast or opacity. In color measurement, a sample is measured over a white background, then over a black background and the ratio expressed either as  a perctentage (where 100% = complete opacity) or as a ratio to 1.  (

crazing, n – a network of apparent fine cracks on or beneath the surface of materials, such as in transparent plastics, glazed ceramics, glass, or clear coatings.

daylight illuminants, CIE, n -- series of illuminant spectral power distribution curves based on measurements of natural daylight and recommended by the CIE in 1965. Values are defined for the wavelength region 300 to 830 nm. They are described in terms of the correlated color temperature. The most important is D₆₅₀₀ (often referred to as average daylight) because of the closeness of its correlated color temperature to that of Illuminant C = 6774 K. D₇₅₀₀, bluer than D₆₅₀₀ and D₅₀₀₀, yellower than D₆₅₀₀, are also used.

densitometer, n – instrument designed for measuring optical density of a photographic negative or positive or a printed image; not suitable for colorimetry.

densitometry, n – technique for measurement of optical density by use of a densitometer.

detector, n – device to convert radiant energy (light) into a neural signal (such as the eye) or an electrical signal (such as a phototube, photomultiplier tube, photocell, photodiode, or the like).

diffuse reflection, n – reflection in which flux is scattered in many directions by diffusion at or below the surface.

directionality, n – (1) perceived, the degree to which the appearance of a surface changes as the surface is rotated in its own plane, under fixed conditions of illumination and viewing. In color the addition of metal flake and or pearlescent pigments will greatly increase the visual color effects. Surface striation and texture may also greatly change color appearance. (2) measured –- (scattering indicatrix, azimuthally nonisotropic) – difference in pattern of near-specular and semidiffusely scattered light, dependent upon the azimuthal angles of the incident and viewing beams.

dominant wavelength, n – the wavelength of a spectrally pure light that, when added to a reference achromatic (white) light, will produce a combination that matches the color of a specimen light.

Delta D ,n -indicates deviation or difference.