Imagine you want a delivery of t-shirts in a particular shade of green, and you are supposed to give your supplier a precise description over the telephone of the color to be produced. Do you think that the t-shirts would be the right color? Highly unlikely.

We need aids - called color spaces - in which every color can be described and classified unambiguously. Attempts were made ever many years to find a color space that was both easy to interpret and had equal intervals in all color areas. Various systems evolved from this. These are the most important systems in colorimetry today.

At first, the CIE X,Y and Z tristinulus values were used to descript color. X related to the observer's red tristimulus, Y to the green stimulus and Z to the blue stimulus. Y also relates to the perception of lightness. It can be useful to display the hue and chroma of a color without considering its lightness. To do this, CIE chromaticity coordinates x and y were calculated from the tristimulus values, and then plotted on a CIE x,y chromaticity diagram. With x and y chromaticity coordinates, the CIE tristimulus values Y was used to represent a color's lightness.

The CIELAB color space is an improvement over the CIE X,Y and Z color space. Three color values L* (lightness), a* (red-green axis), b* (blue-yellow axis) or L* (lightness), C* (chroma/saturation) and h (hue/shade) are calculated from the CIE tristimulus values.

The lightness (L*) ranges between 0 = black to 100 = white. Positive a* values represent red hues and negative a* values represent green hues. Positive b* values represent yellow hues and negative b* values represent blue hues. The chroma (C*) is 0 for a purely achromatic color and increases as the color becomes more brilliant. Hue (h) is an angle from red at 0 degree through yellow at 90 degree, through green at 180 degree and back to red. For example, a light, brilliant orange could have the values L*=70, C*=56.6, h=45 degree, or L*=70, a*=40, b*=40.