COJO 256 → DESIGN RESOURCES → COLOR GLOSSARY

Color glossary

Red, green and blue light projected on a white surface will produce white light where the three additive primaries overlap.

additive primary colors
The primary colors of light, from which all other colors can be made — red, green, and blue. Adding 100 percent of all three produces white light, while adding lesser intensities produces a gamut of different colors. Combining 100 percent of two additive primaries produces a subtractive primary:
  • red+green=yellow
  • red+blue=magenta
  • green+blue=cyan

See also Primary Colors, Subtractive Primaries.

black
The absence of light. The color that is produced when an object absorbs all light.

When the maximum intensity of the subtractive primaries — cyan, magenta, and yellow — are combined, the resulting color should, in theory, be black. Color film, for example, produces black using only cyan, magenta, and yellow dyes. Printing inks, however, are less colorimetrically pure than film dyes, and combining 100 percent cyan, magenta, yellow inks yields a muddy brown; hence, black ink is added as a fourth color ink. Black is abbreviated as “K” in CMYK to avoid confusion with “B” for blue.

blue
One of the three additive primary colors, centered around a wavelength of approximately 436 nanometers.
brightness
The degree to which a color sample appears to reflect light. This attribute of color is used in the HSB (Hue, Saturation, Brightness) color model.
calibration
The act of adjusting a device to bring its behavior into accordance with a known specification. For example, monitors are calibrated to a specific color temperature, gamma, and black and white luminance. Imagesetters and platesetters are calibrated to make sure that they deliver the requested dot percentage accurately. Calibration is typically accomplished by measuring the behavior of a device with an instrument such as a colorimeter or densitometer, comparing the measured behavior with the standard to which the device is being calibrated, then adjusting the device so that it behaves in accordance with that standard.
characterization
The act of describing a device’s behavior through software. In color management, this typically means creating an ICC profile.
chroma
The property of a color that makes it appear saturated, or strongly colored. Black, white, and gray have no chroma. A red tomato is high in chroma. Pastel colors are low in chroma. This attribute of color is used in the LCH (Lightness, Chroma, Hue) color model.

The CIE XYZ (1931) color space rendered as a two-dimensional diagram using chromacity coordinates.

chromaticity Coordinates
Coordinates that describe the hue and saturation, or red-greenness and yellow-blueness, of a color, excluding its lightness. Usually plotted on a two-dimensional plane of constant lightness. An example is the CIE XYZ diagram.
CIE (Commission Internationale de l’Eclairage)
The international standards organization responsible for setting standards for color and color measurement. (The French name translates to “International Commission on Illumination.”)
CIE XYZ (1931)
The first of a series of mathematical models produced by the CIE that describe color in terms of synthetic primaries based on human perception. The primaries are imaginary mathematical constructs that model our eyes’ response to different wavelengths of light. Such models allow us to specify perceived color unambiguously, unlike models such as RGB and CMYK, which define amounts of colorants rather than actual colors.
CIELAB
A mathematical derivative of CIE XYZ (1931) that describes colors using three synthetic primaries: L (Lightness), A (indicating red-greenness), and B (indicating yellow-blueness).

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CMM (Color Matching Method)
A software component that adjusts the numerical values that get sent to, or received from, different devices so that the perceived color they produce remains consistent. The “engine” in color management systems.
CMY
Cyan, magenta, and yellow — the subtractive primary colors — or a color space that describes colors in terms of their cyan, magenta and yellow components.
color
The human perceptual response to different wavelengths of light on the photoreceptors in the retina.
color management
A set of software technologies that seeks to match color across input, display and output devices by referencing their color behavior to a known standard by means of device profiles. The signals each device receives are adjusted in such a way that the perceived color remains consistent.

Paul Gauguin, Femmes de Tahiti (Sur la plage) (1891). Gauguin uses warm colors to portray the sunny South Pacific island.

color model
A means of specifying color numerically, usually in terms of varying amounts of primary colors. Examples include RGB, CMYK, and CIELAB.
color space
A three-dimensional representation of the colors that can be produced by a color model. The universe of colors a color model can produce.
color temperature
  1. A measurement of the color of white light, expressed in Kelvins. (The Kelvin scale is a measure of temperature, starting from absolute zero.) The color temperature is the color of light a perfect black-body radiator emits when heated to that temperature. Computer monitors typically have a color temperature of 5000-9300 Kelvins; 5000 Kelvins is a yellow-white, 9300 Kelvins is a blue-white.
  2. The use of terms such as hot, warm or cool to describe the emotional effects of color. Red, yellow and orange are considered hot or warm colors; blues and greens are considered cold or cool colors.
colorants
Materials used to produce color, such as dyes, inks, pigments, toners, or phosphors.

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colorimeter
An optical instrument that measures the relative intensities of red, green, and blue light reflected or emitted from (or transmitted through) a color sample. Typically used to measure color from computer monitors.

Rods and cones on the retina of the eye. These are the photoreceptors that enable us to see.

cones
The specialized photoreceptors in the human eye that allow us to discriminate between different wavelengths of light. Our eyes contain three distinct types of cones, designated the L, M, and S cones because they are primarily sensitive to long, medium, and short wavelengths of light. (The other type of photoreceptor in the eye are known as rods. They are primarily used in low-light and peripheral vision and do not contribute to color vision.)
cyan
One of the subtractive primary colors. Cyan colorants absorb all red light, reflecting green and blue.
D50
The CIE Standard Illuminant that represents a daylight-correlated color temperature of 5000 Kelvins. Widely used as a standard for viewing booths in the printing industry.
D65
The CIE Standard Illuminant that represents a daylight-correlated color temperature of 6500 Kelvins. Widely used as a standard color temperature for calibrated monitors.
delta error (delta-E)
A measurement of color difference. In theory, delta-E is the smallest color change someone with normal color vision can detect.
densitometer
An instrument that measures optical density.
density
The ability of a material to absorb light. The darker the material, the higher the density. Density is usually expressed on a logarithmic scale of Optical Density (O.D.) units.
device-dependent
Describes a color space defined in terms of physical colorants, such as a monitor’s RGB or a printing press’ CMYK. So called because the actual color produced from a set of device-dependent values depends on the colorants and physical properties of the device in question.
device-independent
Describes a color space defined using synthetic primaries based on human perception, independent of the properties of any physical device. Device-independent color models provide an unambiguous description of perceived color, unlike device-dependent color models.
dynamic range
The range of density that a film stock, digital camera, scanner, or measuring instrument can detect, from the lowest to the highest, usually expressed in O.D. (Optical Density) units. The lowest density is termed dMin, the highest density is termed dMax.
flat color
Color that is one solid color. Photographs might have areas that look like solid color, but usually the pixels have small variations. In areas of flat color on a computer screen, every pixel is exactly the same color. On a printed page, flat colors have evenly sized and distributed halftone dots.

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A representation of selected color gamuts. Specific devices, such as computer screens, have their own gamuts.

gamut
The range of color a device can produce, or the range of color a color model can represent.
gamut compression
The process where a large color gamut (for example, that of transparency film) is reduced to fit the smaller gamut of a print or display process (for example, color printing).
HSB Color Model
A color model that describes color in terms of hue, saturation and brightness.
hue
The property of a color that is identified by a color name, such as red, green or blue. Used as a primary in the HSB (Hue, Saturation, Brightness) color model.
indexed color
Images using indexed color, as GIF files, display 256 colors selected from a palette of 16,777,216 colors. Also called 8-bit color.
Kelvin (K)
Unit of measurement of color temperature. The Kelvin scale starts at absolute zero (-273° Celsius).
LCH Color Model
A derivative of CIELAB that uses cylindrical coordinates of lightness, chroma, and hue instead of the rectangular coordinate system of Lab.
light
That small part of the electromagnetic spectrum whose wavelengths lie in the range of 380 to 720 nanometers and are detectable by the human eye.
lightness
The degree to which a color sample appears to reflect light. This attribute of color is used in the LCH (Lightness, Chroma, Hue) color model.
magenta
One of the subtractive primary colors. Magenta absorbs all green light, reflecting red and blue.

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nanometer
A unit of length equal to one-millionth of a millimeter. Visible light wavelengths are measured in nanometers.
phosphors

A monochrome image, with only black and white pixels. It uses dithering to simulate gray.

Chemical compounds that emit light when struck by a beam of electrons. The amount of light emitted is proportional to the intensity of the electron beam. RGB monitors use three different phosphors to produce red, green, and blue light.
photoreceptor
A mechanism that emits an electrical or chemical signal that varies in proportion to the amount of light that strikes it. CCD (charge-coupled device) sensors in desktop scanners and digital cameras, PMT (photomultiplier tubes) in drum scanners, and the rods and cones in the human retina are all photoreceptors.
pigment
An insoluble colorant (as opposed to dyes, which are soluble). Pigments generally have better fade-resistance and permanence than dyes.
pixel depth
The amount of memory alotted to each pixel on a computer screen. Early computers dedicated on bit of memory to each pixel, allowing only two states, black and white. These monochrome monitors simulated grayscale images by dithering. Today computers have dedicated color processors and memory, and can display millions of colors.
primaries
The components of a color in a color model. They may be actual primary colors perceivable by humans, as in RGB or CMYK, or they may be imaginary mathematical constructs, as with CIE XYZ (1931) or CIELAB.
primary colors
The colors from which all other colors can be made. The primary colors of light are red, green, and blue. These are the additive primaries, used for transmissive or emissive color. The primary colors of pigments are cyan, magenta, and yellow, used for reflective color. It’s possible to create all colors from primary colors because the human eye contains three types of color-sensitive photoreceptors that are sensitive to the individual primary colors.
profile
A data file that describes the color behavior of a physical device (such as a scanner, monitor, or printer) or that defines the color of an abstract color space (such as Adobe RGB 1998 or ColorMatch RGB) in terms of a device-independent color model (such as CIELAB or CIE XYZ). Used by color-management systems to define and match color.
relative colorimetric rendering
One of the four ICC-specified rendering intents used for handling out-of-gamut colors in color matching. Relative Colorimetric rendering first scales the white of the source space to the white of the target space, adjusting all other colors relative to that white. Then it matches the adjusted colors in the source space that are inside the gamut of the target space exactly, and clips out-of-gamut colors to the nearest reproducible hue, sacrificing lightness and saturation.
rendering intent
A method of handling out-of-gamut colors when matching one color space to another. The ICC profile specification specifies four rendering intents: Perceptual, Absolute Colorimetric, Relative Colorimetric, and Saturation.

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saturation
The property of a color that makes it appear strongly colored. Black, white, and gray have no saturation. A red tomato has high saturation. Pastel colors have low saturation. Also known as Chroma. (This attribute of color is used in the HLS (Hue, Lightness, Saturation) and HSB (Hue, Saturation, Brightness) color models.
saturation rendering
One of the four ICC-specified rendering intents used for handling out-of-gamut colors in color matching. Saturation rendering maps fully-saturated colors in the source space to fully saturated colors in the target space, sacrificing hue and lightness.

Cyan, magenta and Yellow are the subtractive color primaries. Black is produced where they all overlap; as color is subtracted, the image moves closer to white.

spectral data
The most complete and precise means of describing a color, by specifying the amount of each wavelength that the sample reflects. Typically, spectral data records the amount of reflected light in 10-nanometer or 20-nanometer bands.
spectral power distribution
The amount of light a light source produces at each wavelength.
spectrophotometer
An instrument that measures the amount of light a color sample reflects or transmits at each wavelength, producing spectral data.
subtractive primaries
Cyan, magenta, and yellow. Used to create reflective color. Cyan absorbs (subtracts) all red light, reflecting blue and green. Magenta absorbs all green light, reflecting blue and red. Yellow absorbs all blue light, reflecting red and green.
tri-stimulus
The practice of specifying or creating colors using three stimuli. These may be additive (RGB) or subtractive (CMY) primary colorants; three attributes such as Lightness, Chroma, and Hue; or three purely synthetic mathematical constructs, as with CIE XYZ (1931) or CIELAB.
tristimulus data
The three values used to define or create a color, such as Red 255, Green 0, Blue 0. Tristimulus values alone do not define a color unambiguously: The illuminant (light source) must also be defined. In the case of device-dependent tristimulus values such as monitor RGB, the primaries must also be defined in a device-independent system such as CIE XYZ or CIELAB. Tristimulus values can always be computed from spectral data, but spectral data cannot be inferred from tristumulus values.

The electromagnetic spectrum. Visible light makes up only a small part of the spectrum, from 380 to 720 nanometers.

visible spectrum
The portion of the electromagnetic spectrum with wavelengths between 380 and 720 nanometers. Wavelengths in this range provoke the sense of color when they impinge on the photoreceptors in the human retina. The shorter wavelengths within this range produce blue and violet sensations; the longer wavelengths produce orange and red sensations.
yellow
One of the subtractive primary colors. Yellow absorbs all blue light, reflecting red and green.

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COMMUNICATION AND JOURNALISM 256 | UNIVERSITY OF ST. THOMAS | © 2017 | INSTRUCTOR: Michael O’Donnell | mjodonnell@stthomas.edu | 651-962-5281

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