Color Glossary A-C

A B C [ D E F G H I J K L M N O P Q R S T U V W X Y Z ]

Version 1.0, 03/18/2003

The following glossary lists and explains color and visual perception terms which are relevant for graphic and Web design as well as usability. The information was taken from several sources and adapted to the needs of this glossary. See References for more information.

In this version, some ISO definitions have been added.

Accomodation

ISO Definition: Adjustment of the focus of the eye, normally spontaneous, for the purpose of attaining maximum visual acuity at various distances. (Source: ISO 8995 (1989-10-00) ISO/TC 159)

Achromatic Colors

The "hueless" colors black, gray, and white, that is, the whole range of gray levels between black and white.

ISO Definition: Perceived colors devoid of hue. The color names white, gray and black are commonly used or, for transmitting objects, colorless and neutral. (Source: ISO 9241-8 (1997-10-00) ISO/TC 159)

Figure: Achromatic "colors".

Adaptation (visual)

ISO Definition: Process by which the state of the visual system is modified by previous and present exposure to stimuli that may have various luminances, spectral distributions and angular subtenses. (Source: ISO 9241-8 (1997-10-00) ISO/ TC 159)

Adaption

ISO Definition: The process which takes the luminance and/or the colour of the visual field or the final state of this process. (Source: ISO 8995 (1989-10-00) ISO/TC 159)

Additive Color

Synonym for the RGB (red, green, blue) color space that uses the projected red, green and blue light as primary colors to produce the full spectrum of colors. See also Color Mixture -> Additive Color Mixture.

Figure: The primaries of additive color mixing are red, green, and blue.

Additive Color Mixture

See Color Mixture -> Additive Color Mixture.

Afterimages

Afterimages result from localized adaptation of the photoreceptors in those parts of the retina exposed to the stimulus.

Monochrome Afterimages

If a black object on a white background (or vice versa) is being focused on for several seconds, and then a white area is being focused on, a negative afterimage is perceived. The afterimage may last for one to two minutes.

Figure: Monochrome afterimage - glare at the dots for several seconds and you will begin to see a negative afterimage, i.e. white dots

Color Afterimages

If a colored area is being focusd on for a longer time (at least for about half a minute), and then a white area is being focues on, an afterimage of the complementary color is perceived. The afterimage may last for one to two minutes.

Figure: Color afterimage - gaze at the center of the image for about 30 seconds and then look away to a neutral area - an afterimage of the Union Jack will be seen.

-> Large areas of bright color should be avoided on screens because of the disturbing afterimages that can result.

Aliasing

Makes individual pixels visible, especially along diagonal lines and curves. Also known as staircasing or Jaggies because of the steps that appear. Lines and text look more jagged than smooth.

Figure: Aliased (normal) lines (left) vs. anti-aliased (smoothed) lines (right)

Figure: Enlarged sections of the image above

See Anti-Aliasing.

Anti-Aliasing

A process that filters or softens the hard stair-stepped edge (and thus removes the Jaggies) in bitmapped images by creating a series of gradually blending pixels.

Figure: Aliased (normal) text (left) vs. anti-aliased (smoothed) text (right)

Figure: Enlargement of the image above

Note: Anti-aliasing increases the number of colors in a digital image. Therefore, Web designers sometimes prefer aliased text in order to keep the file size small.

See Aliasing.

BMP

See Image File Formats.

Brightness

Brightness is the perceived intensity of light coming from the image itself, rather than any property of the portrayed scene. Brightness is sometimes defined as perceived luminance. (From Adelson, MIT)

Brightness Assimilation

Figure: The gray under the white stripes appears lighter than the same gray under the black stripes due to brightness assimilation

See also Color Assimilation.

Brightness Contrast

See Simultaneous Contrast -> Simultaneous Contrast (Black and White).

See also Simultaneous Contrast -> Simultaneous Color Contrast.

Chroma

Synonym for Saturation.

Chromatic Colors

The "colorful" colors like, red, green, blue, yellow, purple, etc.

Figure: The chromatic primaries of additive color mixing are red, green and blue.

Chromatic Induction

Synonym for Hue Induction.

Chromostereoopsis

Red and blue colors are perceived at different depths. This effect is due to the chromatic aberration of the eye (light of different wavelengths is refracted differently).

Figure: Foreground and background color combinations to avoid!

Because chromostereoopsis can be quite disturbing visually, avoid displaying both vivid red and blue together.

CIE

Commission Internationale de l'Eclairage - this commission determines standards for color and lighting. It developed the Norm Color system and the Lab Color Space (also called Lab Color System, or CIELAB Color System).

CMYK

See Color Space -> CMYK (see also RGB, HSL/HSV/HSB, Lab).

Figure: The primaries of the CMYK color space are cyan, magenta, yellow, and black

Color After Images

See After Images -> Color After Images.

Color Assimilation

Color assimilation (also known as the Von Bezold spreading effect or Bezold-Brücke effect) is the opposite of Color Contrast: Colors take on the hue of the surrounding color, whereas color contrasts moves it into the direction of the Complementary Color.

Example: The white squares on the red background in the figure below look reddish, and those on the blue background look bluish. Thus, the white squares tend to take on their background's colors.

Figure: The white central square shifts its hue into the direction of the surrounding color.

While the physiological mechanisms for brightness and color contrast phenomena are well understood, the conditions how and when the assimilation occurs are not. However, as with the brightness assimilation, the spatial frequency (coarseness) of the image seems to be an important factor.

Figure: Animated demonstration of color assimilation; look how the same color looks differently depending on the surrounding colored triangles.

Figure: Image comparable to the image for brightness assimilation - the yellow under the red stripes appears warmer than the same yellow under the blue stripes due to color assimilation

The contrast and assimilation phenomena are also found for brightness and darkness (Brightness Contrast and Brightness Assimilation).

See also the Illusion Forum Website for animated demonstrations of many effects.

Color Blindness

See Color Deficiencies; see also Visual Impairments.

Color Circle

Newton's color circle is a convenient way to summarize the additive mixing properties of colors (see second figure below). R, G, B are thought of as the additive primary colors, and their complementary colors are placed across from them on the circle. The colors then fall on the circle in the order of the wavelengths of the corresponding spectral colors. Magenta (purple) is not a spectral color.

Figure: A color circle (from Apple Macintosh)

Figure: Using the color circle to predict the outcomes of additive color mixing (adapted from Hyperphysics)

Saturation (purity of the color) can also be described by the color circle: colors become less pure or desaturated as you move into the center of the circle; colors become purer or saturated as you move towards the perimeter.

Quantifying the circumference of the circle in terms of hue and its radius in terms of saturation leads toward one of the formal color systems, the Munsell System. (Adapted from Hyperphysics Website)

Color Constancy

The human ability to maintain the percept of a particular hue throughout variations in the quality of the luminance or reflectance properties of the surface pigment. (Adapted from Sensation and Perception)

Color Contrast

See Simultaneous Contrast -> Simultaneous Color Contrast.

Color Deficiencies

Some individuals show drastic deficiencies in their ability to discriminate colored stimuli - these people are called colorblind, although this term is too strong for most of the deficiencies. According to the trichromatic color theory there are five types of color deficiencies to be distinguished:

• Monochromats
  • Monochromats I: people with no functioning cones; people with this deficiency have problems with daylight, because it is too bright for them; they also lack visual acuity
  • Monochromats II: people with only one variety of the cones functioning in addition to the rods; both types of monochromats see colors only as variations in intensity, that, is analog to black-and-white or unicolored images
• Dichromats: People with only one malfunctioning cone system
  • Protanopia: malfunctioning in the red cone system; typically only two (yellow, blue) or three colors (yellow, blue, purple) can be distinguished - yellow comprises red, orange, yellow, and green, blue coincides with blue and purple
  • Deuteranopia: malfunctioning in the green cone system; green cannot be distinguished from certain combinations of red and blue; this is the most common type of color deficiency
  • Tritanopia: malfunctioning of the blue cone system; longer wavelengths appear as red and the shorter ones as bluish-green; this color deficiency is very rare

Mild instances of color deficiencies are called "anomalous trichromatism" and are fairly common; typically these people do not act exactly like a dichromat, but need more red (protoanomaly) or green (deuteranomaly) than a color-normal individual to match colors. More than 8% of the male and about 0.04% of the female population have some sort of color anomaly or deficiency. (Adapted from Sensation and Perception)

Figure: Ishihara color blindness test charts (from Allendale Eyecare Website)

See also www.visibone.com/colorblind. Test your color vision at Michael Bennett's Website (http://home.sc.rr.com/mikebennett/colorblind.html). Visicheck offers a color deficiency simulator (http://www.vischeck.com/)

For visual impairments in general, see Visual Impairments.

Color Induction

See Hue Induction (also called chromatic induction).

Note: The term color induction is used with different meanings.

Color Mixture

Additive Color Mixture

Additive color mixing describes how different wavelengths of light mix to make colors in the mind. This color mixing is explained through the combinations of the "primary" colors red, green, and blue (RGB). Color mixtures are usually demonstrated by shining overlapping beams of light through different color filters onto a white (colorless) surface (as in the diagram below), or by patches of pure colored paper or paint on a rapidly spinning disk (a "color top" or "Maxwell disk," so named because James Clerk Maxwell used it to study color mixing in around 1855, although it was first used for that purpose by Ignaz Shiffermüller in the 1760's).

Figure: Additive color mixing using light sources (from www.linocolor.com)

Any color can be produced by adding the colors of the three color channels RGB (Red, Green, and Blue). If the colors of two of the color channels are mixed in equal proportions, new base colors are created. Blue and green add up to a bright, light blue called cyan. Magenta, a bright pink, is made by mixing red and blue. Red and green together make yellow. If red, green, and blue light are mixed equally together at full power, you get white light. (Adapted from www.linocolor.com)

Figure: Mixing two colors additively leads to a lighter color; if red, green, and blue light are mixed equally together at full power, you get white light (from www.mica.edu)

Monitors

Monitors and televisions produce color by using electromagnetic waves that correspond to red, green and blue. However, screens aren't able to display the full range of colors which are visible to the human eye. Their range of color is limited. (From www.linocolor.com)

See also the Hyperphysics Website.

ISO Definition: Stimulation that combines on retina the actions of various color stimuli in such a manner that they cannot be perceived individually. (Source: ISO 9241-8 (1997-10-00) ISO/TC 159)

Subtractive Color Mixture

The opposite of additive color mixing, subtractive color mixing describes how the light absorbing properties of paints mix to make colors in reflected light. This color mixing is explained through combinations of the three subtractive "primary" colors cyan, yellow and magenta (CYM), and is usually demonstrated by placing multiple color filters over a single beam of light, or by physically mixing paints (i.e. inks or pigments that reflect light of a certain color). That is, the subtractive primary colors result when a section of the visible spectrum corresponding to a single additive primary color is absorbed from reflected white light. (Adapted from www.linocolor.com)

Figure: Mixing colors subtractively leads to a darker color (from www.mica.edu)

How Colors Are Printed

Printed colors differ from monitor colors in that they are produced by overlaying ink pigments on paper instead of by combining different wavelengths of light. If you tried to print red, green, and blue on top of one another, however, you could not produce many colors. You would not be able to make yellow, for instance. That is why printing uses subtractive instead of additive color mixing. (From www.linocolor.com)

Why the K?

Theoretically, if we were to print a surface with equal parts of cyan, magenta and yellow, we would see black, because all colors would be absorbed and none reflected. In practice, however, this black looks more like a muddy green or brown. That is why four colors are generally used in printing ("four-color print"). Black (K) is used as the fourth color in order to achieve a real black. (From www.linocolor.com)

Color Model

See Color Space.

Color Space

The Color Space

To integrate brightness into the picture, the color triangle must be transformed from a two-dimensional triangle into a spatial body known as color space. The color space is a three-dimensional system with coordinates for red, green and blue:

Figure: The color space extends the color triangle into three dimensions

The further the color loci of the primary colors from the origin, the greater the volume of the cuboid color gamut which is formed and thus the higher the quality of any color reproduction system which is based on it.

All colors lying inside the color gamut can be reproduced by a reproduction system based on the primary colors (for example a color monitor). Colors outside the color space cannot be reproduced.

In other words: the primary colors of a color space are determined by the equipment which generates them. (From www.linocolor.com)

RGB

Color space based on the three primary colors red (R), blue (B) and green (G) used for additive color mixing. Televisions and computer monitors use RGB to reproduce color.

Figure: The three primaries of the RGB color space are red, green and blue

CMYK

Color space based on the three primary colors cyan (C), yellow (Y) and magenta (M) used for subtractive color mixing, plus the achromatic color black (K). The four process colors used in four-color printing.

Figure: The four primaries of the CMYK color space are cyan, magenta, yellow and black

HSL, HSV, HSB

Hue, Saturation, Luminance (also known as Hue, Saturation, Value or Hue, Saturation, Brightness): A system for describing the physical perception of color, in terms of tint (hue, color tone), perceived narrowness of the spectrum (saturation, chroma), and luminance (brightness, value).

Hue determines the position on the color wheel or color circle, Saturation is the purity of the color, and Luminance the range of lightness to darkness of the color.

Application of the Model

In the HSL color space it is easy to change hue, saturation and luminance alone without changing the other two characteristics; this is hard to achieve in the RGB color space that is offered by most graphic programs.

Hue can be changed by moving the position on the color circle:

Figure: Hue changes by moving the position on the color circle (from Hyperphysics)

Saturation: If, for example, blue is gradually added to a yellow, mixed from red and green, the yellow goes through steps of decreasing purity, each "less chromatic."

Figure: Demonstration of adding blue in steps of 25% to yellow, represented as a mixture of 100% red and 100% blue

Colors of different saturation retain their original hue since the relationship between the color values of red and green are not changed. In the color triangle, they move along the straight connecting line from the yellow color locus towards blue, whereas in the color circle increasing saturation corresponds to a radial outward movement:

Figure: Saturation increases by moving outwards on the color circle (from Hyperphysics)

Brightness

If all three color components are reduced simultaneously -- while retaining their mixing ratio -- the hue remains unchanged. The color decreases in brightness. If the components of all three primary colors are reduced to zero, the resulting color will be black. Like white, black has a saturation level of zero.

Figure: Demonstration of decreasing the brightness of pure blue in steps of 25%

See also Lightness, Luminance.

Figure: All three dimension in the color circle (from Hyperphysics)

Norm Color System

In 1931 the CIE ( Commission Internationale de l'Eclairage) developed the XYZ color system, also called the "norm color system." This system is often represented as a two-dimensional graphic which more or less corresponds to the shape of a sail.

Figure: The XYZ color space defined by the norm color system (from www.linocolor.com)

The red components of a color are tallied along the x (horizontal) axis of the coordinate plane and the green components along the y (vertical) axis. In this way every color can be assigned a particular point on the coordinate plane. Colors on the left tend toward gray, which means that their spectral purity is decreased.

What is not taken into consideration in this graph is brightness (the z axis). If it were, the figure would look like a flat sack. (From www.linocolor.com)

Color spaces can be drawn for different devices (eyes, printer, screen) for comparisons.

Figure: Relative gamuts of additive (monitor display) and subtractive (printed) color; the larger area on the graph represents all visible colors. Click on the graph to see a more detailed version of the chart. (from projectcool Website)

See also Color Triangle.

CIELAB, Lab, L*a*b

Color space defined by the CIE, based on one channel for Luminance (lightness) (L) and two color channels (a and b).

One problem with the XYZ color system, is that colorimetric distances between the individual colors do not correspond to perceived color differences. For example, in the figure above, a difference between green and greenish-yellow is relatively large, whereas the distance distinguishing blue and red is quite small. The CIE solved this problem in 1976 with the development of the three-dimensional Lab color space (or CIELAB color space).

In this model, the color differences which you perceive correspond to distances when measured colorimetrically. The a axis extends from green (-a) to red (+a) and the b axis from blue (-b) to yellow (+b). The brightness (L) increases from the bottom to the top of the three-dimensional model. (From www.linocolor.com)

Figure: The CIELAB color space (from www.linocolor.com)

This color space is better suited to many digital image manipulations than the RGB space, which is typically used in image editing programs. For example, the Lab space is useful for sharpening images and the removing artifacts in JPEG images or in images from digital cameras and scanners.

Color Triangle

Any three non-collinear points plotted on a chromaticity diagram determine a color triangle. Since the points are non-collinear, they correspond to basic, or primary hues. All of those colors on the chromaticity diagram which fall within the triangle determined by the three points may be produced by addition of the three hues.

Colors in the chromaticity triangle are defined by hue and saturation (chroma) only, not by brightness. There can be any amount of brightness in the chromaticity triangle.

Figure: A basic color triangle (left); using the color triangle for demonstrating relations between colors (right)

All colors which can be produced by additive mixing of the three primary colors red, green and blue lie in the area enclosed by this color triangle. The further a color lies from the center of the triangle the higher its saturation (chroma). A mixed color has a high saturation level if it has only a small amount of its third component. A maximum saturation is found in colors mixed from only two primary colors.

If the amount of the third primary color is increased until all three primaries are present in equal components, white is the result - the saturation level is equal to zero, and the achromatic point lies in the middle of the color triangle (see color triangle above).

Figure: Adding blue in steps of 25% to yellow, represented as a mixture of 100% red and 100% blue, eventually leads to white

Color Wheel

A color wheel arranges colors around the edges of a circle. Primary colors are in the middle. Three common color wheels are the artist's wheel, the subtractive wheel, and the additive wheel (see below). A standard color wheel has 12 distinct hues, but does not have any visual information about saturation or value. These 12 hues can be classified in:

• Primary colors - the defining colors of the wheel; in the color wheels below, they appear in the center as well as equally spaced around the circle
• Secondary colors- the three colors that are equal distant from the primary colors
• Tertiary colors - the colors between each primary and secondary color

The Artist's Color Wheel This color wheel is used for mixing paints. It uses red, yellow, and blue as primary colors. Violet, green, and orange are secondary colors, and red-violet, blue-violet, blue-green, yellow-green, yellow-orange, and red-orange are tertiary colors.
The Subtractive Color Wheel This color wheel uses the printing inks cyan, magenta, and yellow as primary colors. Note: Because cyan (C), magenta (M), and yellow (Y) inks do not combine to make black, the printing process adds black as a fourth ink (K).
The Additive Color Wheel This color wheel displays the additive colors used for projected light. When mixed together the additive primaries form white. The primaries are red, green and blue. These colors are extremely bright because light that is projected can be far more intense than printed color.

(Adapted from projectcool Website)

Complementary Colors

Colors that add to white when mixed adaptively. Complementary colors reside at opposite ends of the Color Circle or Color Wheel.

Examples: Magenta-green, blue-yellow, red-cyan

Figure: Complementary colors reside at opposite ends of the color circle (left) or color triangle (right)

Complementary Colors - The Traditional Color Wheel

Complementary colors are those that are situated across from each other on the color wheel. There is a unity inherent in using complementary colors since any color has as its complement the sum of the other two primary colors. The complement of yellow, for instance is purple, made by mixing the other two primaries, red and blue. The complement of red is green, a combination of yellow and blue. Compositions created using complementary color schemes tend to feel complete and pleasing to the eye. Complementary colors will desaturate each other if mixed. (From www.mica.edu)

Complementary Colors - The Scientific Color Wheel

In the scientific color wheel, the symmetry or unity of the relationships of complements is even more evident. These six colors show both the pigment primaries of cyan, magenta and yellow along with the pigment secondaries of red, blue-violet and green. The complement of a primary pigment color turns out to be a primary light color. We could just as easily call this a color wheel for light (an additive wheel) with the primaries being red, blue-violet and green and secondaries of cyan, magenta and yellow. (From www.mica.edu)

Constancies

See Color Constancy and Size Constancy.

Contrast Sensitivity

The contrast sensitivity function for red and green is greatest for 10 point text (spatial frequency = 1 line pair/mm = 8 Hz/degree) at normal viewing distance (46 cm) and about 14 point text at arm length (65 cm).

For blue the greatest sensitivity is around a spatial frequency of 1 Hz/degree The sensitivity itself is about one tenth of that of red and green. This is due to the scarcity of blue cones in the retina and to the absence of a local yellow-blue opponent mechanism. (From Jackson et al.)

Figure: The primaries blue, red and green in normal face and bold face on white and black backgrounds

Cultural Variations in the Meaning of Colors

Overview

(from different sources)

Color Associations

These associations are valid for western cultures only (see table above for differences). (from Jackson et al.)

The Achromatics

White

• Positive: Snow, Purity, Innocence, Peace, Lightness, Cleanliness
• Negative: Cold, Clinical, Vulnerability, Deathly pallor, Surrender, Sterility

Black

• Positive: Night, Coal, Power, Stability, Formality, Solidity
• Negative: Fear, Void, Death, Secrecy, Anonymity, Evil

Gray

• Positive: Intelligence, Maturity, Wealth, Dignity, Dedication, Restraint
• Negative: Confusion, Decay, Concrete, Shadow, Depression, Boredom

The Chromatic Primaries

Red

• Positive: Victory, Passion, Love, Strength, Energy, Sexuality
• Negative: Blood, War, Fire, Danger, Anger, Satan

Yellow

• Positive: Sun, Summer, Serenity, Gold, Harvest, Innovation
• Negative: Cowardice, Treason, Jealousy, Hazard, Illness, Folly

Green

• Positive: Vegetation, Nature, Spring, Fertility, Hope, Safety
• Negative: Decay, Inexperience, Envy, Greed, Escapism, Bad luck

Blue

• Positive: Sky, Sea, Spirituality, Stability, Peace, Unity
• Negative: Cold, Depression, Melancholy, Obscenity, Mystery, Conservatism

Color Preferences

Eysenck's "universal" order of colors for Western adults:

(1) Blue, (2) Red, (3) Green, (4) Purple, (5) Yellow, (6) Orange

References

Compiled and edited by Christine Wiegand and Gerd Waloszek (Product Design Center)

 top

Source:  Color Glossary