Lab and CIE XYZ color spaces

The Lab color space is itself derived from an earlier reference space, CIE XYZ. In 1931, CIE established a model based on an averaged observers’ visual sensitivity to different wavelengths of light under a specific light source and angle of illumination. From that model, the CIE introduced XYZ tristimulus values and when plotted in 3D form, three coordinates XYZ. In its 2-D form, color is plotted in an elongated n-shaped chart known as the CIE 1931 XY chromaticity diagram.

Lab adopts a 3-D model that uses values that are easier to interpret, with L or Lightness co-ordinate and two a and b color components. The model also closely matches the human color vision, with respect to the perceived differences in color and the distances between them, especially when plotted in a 2-D form using a circular color wheel. However, a Lab coordinate is computed from an XYZ coordinate by “normalizing” to a white-point. This means that under a certain light source, a color that is perceived to have the same color as white is neutral, and will have coordinates, or values, a*=b*=0. In Lab, that light source is D50.

<<   The capture process overview   |   Standard observer   >>