Response of the human visual system to variable illuminant conditions: An analysis of opponent-colour mechanisms in colour constancy

Illuminant changes in a scene generally cause displacements in the chromati city and luminance of the objects of which the scene is composed; however, the visual system is capable of maintaining a constant object colour appear ance independently of the illuminant. This is the phenomenon traditionally known as colour constancy. A classical asymmetric colour-matching experimen t is reported to address two aspects of colour constancy: successive colour constancy and the role of opponent mechanisms in it. To this end, colour m atches are made with chromatically complex backgrounds under different illu minants and with an equal-energy light source as standard. The results are analysed in the cone-excitation space, separately along the L-2M and S dime nsions. Data are presented showing that: colour-vision mechanisms respond d ifferently to illuminant changes when colour constancy is considered at bot h receptoral and post-receptoral levels. The L- and M-cones tend to adapt s o as to support colour constancy, whereas S-cones are strongly influenced b y the illuminant changes. In addition, the data suggest good approaches to colour constancy linked particularly to the yellow-blue mechanism. (C) 1999 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved.