17 - Colorimetry

Summary

The assessment and quantification of color is referred to as colorimetry or the “science of color”. Colorimetry is closely associated with human color vision. Both colorimetry and human vision have attracted a great deal of interest that spans many centuries. For a thorough and entertaining review of the history of colorimetry including early attempts to understand color, we recommended the collection of historical reprints complied by MacAdam (1993).

The human sense of vision is very different from the human sense of hearing. If we hear two frequencies simultaneously, e.g. two frequencies generated by a musical instrument, we will be able to recognize the musical tone as having two distinct frequencies. This is not the case for optical signals and the sense of vision. Mixing two monochromatic optical signals will appear to us as one color and we are unable to recognize the original dichromatic composition of that color.

Color-matching functions and chromaticity diagram

Light causes different levels of excitation of the red, green, and blue cones. However, the sensation of color and luminous flux caused a particular light source varies slightly among different individuals. Furthermore, the sensation of color is, to some extent, a subjective quantity. For these reasons, The International Commission for Illumination (Commission Internationale de l'Eclairage, CIE) has standardized the measurement of color by means of color-matching functions and the chromaticity diagram (CIE, 1931).