Illuminant cues in surface color perception: tests of three candidate cues

Many recent computational models of surface color perception presuppose inf ormation about illumination in scenes. The models differ primarily in the p hysical process each makes use of as a cue to the illuminant. We evaluated whether the human visual system makes use of any of three of the following candidate illuminant cues: (1) specular highlight. (2) full surface specula rity [Lee, H. C. (1986). Method for computing the scene-illuminant chromati city from specular highlights. Journal of the Optical Society of America A. 3(10), 1694-1699; D'Zmura, M., & Lennie, P. (1986). Mechanisms of color co nstancy. Journal of the Optical Society of America A. 3(10), 1662-1672], an d (3) uniform background. Observers viewed simulated scenes binocularly in a computer-controlled Wheatstone stereoscope. All simulated scenes containe d a uniform background plane perpendicular to the observer's line of sight and a small number of specular, colored spheres resting on the uniform back ground. Scenes were rendered tinder either standard illuminant D65 or stand ard illuminant A. Observers adjusted the color of a small, simulated test p atch to appear achromatic. In a series of experiments we perturbed the illu minant color signaled by each candidate cue and looked for an influence of the changed cue on achromatic settings. We found that the specular highligh t cue had a significant influence, but that the influence was asymmetric: g reater when the base illuminant, CIE standard Illuminant A, was perturbed i n the direction of Illuminant D65 than vice versa. Neither the full surface specularity cue nor the background cue had any observable influence. The l ack of influence of the background cue is likely due to the placement of th e test patch in front of the background rather than. as is typical, embedde d in the background. (C) 2001 Elsevier Science Ltd. All rights reserved.