title: Color constancy in natural scenes explained by global image statistics.
abstract: To what extent do observers' judgments of surface color with natural scenes depend on global image statistics? To address this question, a psychophysical experiment was performed in which images of natural scenes under two successive daylights were presented on a computer-controlled high-resolution color monitor. Observers reported whether there was a change in reflectance of a test surface in the scene. The scenes were obtained with a hyperspectral imaging system and included variously trees, shrubs, grasses, ferns, flowers, rocks, and buildings. Discrimination performance, quantified on a scale of 0 to 1 with a color-constancy index, varied from 0.69 to 0.97 over 21 scenes and two illuminant changes, from a correlated color temperature of 25,000 K to 6700 K and from 4000 K to 6700 K. The best account of these effects was provided by receptor-based rather than colorimetric properties of the images. Thus, in a linear regression, 43% of the variance in constancy index was explained by the log of the mean relative deviation in spatial cone-excitation ratios evaluated globally across the two images of a scene. A further 20% was explained by including the mean chroma of the first image and its difference from that of the second image and a further 7% by the mean difference in hue. Together, all four global color properties accounted for 70% of the variance and provided a good fit to the effects of scene and of illuminant change on color constancy, and, additionally, of changing test-surface position. By contrast, a spatial-frequency analysis of the images showed that the gradient of the luminance amplitude spectrum accounted for only 5% of the variance.
authors.affiliation: Sensing, Imaging, and Signal Processing Group, School of Electrical and Electronic Engineering, University of Manchester, Manchester, United Kingdom. d.h.foster@manchester.ac.uk
authors.forename: David H
authors.initials: DH
authors.lastname: Foster
authors.forename: Kinjiro
authors.initials: K
authors.lastname: Amano
authors.forename: Sérgio M C
authors.initials: SM
authors.lastname: Nascimento
mesh_terms: D003116:Color; D003118:Color Perception / Q000502:physiology*; D017076:Computer-Aided Design; D015350:Contrast Sensitivity / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology; D006801:Humans; D008027:Light; D019368:Nature; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics / Q000379:methods; D013028:Space Perception / Q000502:physiology