Introduction

Color is a major criterion for a consumer when he selects and purchases a commercial product; more generally it is a signature associated to each object which makes it recognizable. The notion of color is highly dependent on the nature of the light source, which can be either natural (sun) or artificial (light bulbs). As the perception of color involves a complex processing by the brain, a straightforward definition of color is hard to find, and could not be restricted to something like “the spectrum of the light captured by the human eye”. A more precise definition should include:

1.the properties of the object surface;

2.the quality of visual perception;

3.the nature of the light source;

4.the geometry of observation.

All these parameters are summarized in figure 1.

The visual sensation experienced by an observer exposed to a colored visual stimulus is complex: as our knowledge of human vision mechanisms is still improving, putting color vision into equations is necessarily a “work in progress”, likely to be subjected to constant revision. Historically, the main objective of colorimetry (and of related measurement systems) had been to define visual equivalents of colored stimuli. More recently, its objective has been to supply methods that enable quantifying color matches and color differences, since it is of foremost importance, in a quality procedure, to ensure that the color of a commercial product will be perfectly reproducible.