Color Space is well named since any method used to map and describe color must use three dimensions. The eye records scenes using its achromatic rods and its chromatic red, blue and green cones. Therefore, color is clearly three dimensional and any attempts to reduce color to mathematical equations must utilize three dimensions. Tristimulus Values are mathematically derived from color measurements and represent the amounts of red, blue and green light recorded by the eye of a theoretical Standard Observer. Tristimulus Values are the basic raw numbers used for colorimetric calculations.

Scientific attempts to calculate color have the goal of making the numbers match visual observations. This is difficult because research shows that the eye does not see in a linear fashion. This complicates any attempts to reduce what a person sees to mathematical equations. Equation developments tend to focus on how to handle this nonlinearity.

The following is a list of the better known colorspace equations used for describing color in plastics. There are others, but they are not used very much today.

CIELab CIE L*a*b* CIELab Lch CMC

One of the popular calculations, CIE L*a*b* is usually just referred to as CIELab for ease of conversation and writing. These systems mean little without some description of the letters.

CIE is the abbreviation for the French International Commission on Illumination, Commission Internationale de l'Eclairage

L describes the lightness/darkness of a measured sample. +L is light -L is dark

a describes the red or green of a measured sample. +a is red -a is green

b describes the yellow or blue of a measured sample. +b is yellow -b is blue

c describes the chroma or saturation of a measured sample.

h describes the hue of a measured sample.

It may be helpful to think of CIELab as a rectangular coordinate system and CIELch as a polar or cylindrical coordinate system.

ColorXpress™ Services normally works and calculates color data primarily in CIELab. This calculation is extremely popular in industry. However, ColorXpress™ Services has the capability to work in virtually any system specified by the customer. The method specified other than CIELab usually has a special significance to the application.

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