Introduction

There are numerous colorsystems and -models developed and created from scientists and artists. Even nowadays, new systems are under development, no end in sight. Here you'll get a short introduction into the world of colors. For additional ressources, please visit the links provided in the link section.

Color Basics
Color Models
Color Glossary

Color Basics

Additive Colors

The additive color process is used for light-emitting devices such as CRT displays. All the colors of the rainbow can be produced by mixing the three primary wavelendths of light (red, green, blue). The projection of the three primary colors in equal amounts produces white.

experiment with additive colors (explorescience.com)
information about additive color (apple.com)

Subtractive Colors

The subtractive color process is based on the three primary subtractive colors (cyan, magenta, yellow). In order to produce subtractive colors, a light reflecting object is needed that absorbs certain wavelengths, allowing others to be reflected. Printing and painting is based on the subtractive method. If you mix all three primaries together, the black color is produced.

information about subtractive color (apple.com)

Color Models

RGB Model

RGB stands for the three additive primary colors red, green and blue. Thru additive color mixing, all colors of the RGB-Model can be produced. Monitors and televisions use the RGB-Model to show colors. Each primary color has a value between 0 and 1. R=G=B=1 equals white, R=G=B=0 equals black.

All RGB colors can be shown in a cube. The three primary colors, the three secondary colors (cyan, magenta, yellow) as well as white and black are positioned in the corners of the RGB-cube.

HSV Model

Downside of the RGB model is the difficulty to mix colors. It is not easy to find the right amount of red, green and blue to mix a specific color tone. Mixing colors using the HSV model (hue, saturation, value) is much more intuitive because there is a separate value for the hue.

CMY(K) Model

Displaying colors on a screen is based on the RGB model (additive), whereas printing colors on paper is based on the subtractive CMY(K) model. CMY(K) stands for cyan, magenta, yellow and black. Similar to the RGB model, all CMY model can be displayed in a cube.

CIE Model

The CIE model was defined by the "Commision International de l'Eclairage" in 1931. The three additive primary colors red green and blue are replaced by the standardized primary colors X,Y,Z. The XYZ color space comprises all visible colors. XYZ are virtual colors that are used to display all visible colors with positive algebraic signs. The spectral consistence correlates to the color perception of the human eye: The value of XYZ is proportional to the physical energy of the represented color.

CIE L*a*b Model

The CIE L*a*b model is a common color space, redefined from the original CIE model in 1976. It is based on the human perception of color which is based on the three color receptors of the human eye (red, green, blue). L is the value for the luminance of an object (L = 0 = black, L = 100 = white). The chrominance is defined by the a and b values. The a value stands for red (a is positive) or green (a is negative). The b value stands for yellow (b is positive) or blue (b is negative). The higher the a and b values, the more saturated the color.

YIQ Model

YIQ is used in color TV broadcasting. It is downward compatible with black and white television where only Y is used. Y stands for the luminance (intensity). I and Q determine the chromaticity. I is the red-orange axis, whereas Q is roughly orthogonal to I.

Color Glossary

Gamut

The gamut of colors is all colors that can be produced by using the the three primary colors of the model. Different color models have therefore different gamuts. The CIE Lab gamut covers all colors in the visible spectrum. The RGB gamut is smaller - not all visible colors can be seen on monitors (for example pure yellow / pure cyan). The CMY(K) gamut is even smaller, but not a straight subset of the RGB gamut.

Hue

The hue is determined by the wavelength of a color. Hue is the attribute that differs for example green from blue.

Lightness / Value / Luminance

The lightness or value of a color equals the physical intensity.

Primary colors / Primaries

Additive color models are based on the three primary colors blue, red and green. Substractive color models are based on the primaries cyan, magenta and yellow.

Saturation

A saturated color only reflects one or two out of the three primaries. If you add the third primary, the color will be desaturated, it will change towards white, gray or black.