In contrast to the CIE (Commission Internationale de l'Eclairage) colorimetric systems in which colors are specified on the basis of spectrum of light, a system for surface color is displayed by the standard chips. According to the principle by which the standard chips are selected and arranged, we have many different systems. Three representative systems are examined, Munsell, OSA-UCS (Optical Society of America-Uniform Color Scale), and NCA (Natural Color System) of Sweden. Each is a systematization of human cognition of colors, and how we see the difference between two chips j and k plays a different role in each spatial representation. On the basis of observers' assessments, the perceptual difference is scaled as d jk, a numerical value. The structure of each system is quantitatively examined by checking the behavior of d jk. This article is a review of the author's studies in this line.
Color vision; colorimetry; psychophysical scaling; multi-dimensional representation
