Spatial distributions of local illumination color in natural scenes.
In natural complex environments, the elevation of the sun and the presence of occluding objects and mutual reflections cause variations in the spectral composition of the local illumination across time and location. Unlike the changes in time and their consequences for color appearance and constancy, the spatial variations of local illumination color in natural scenes have received relatively little attention. The aim of the present work was to characterize these spatial variations by spectral imaging. Hyperspectral radiance images were obtained from 30 rural and urban scenes in which neutral probe spheres were embedded. The spectra of the local illumination at 17 sample points on each sphere in each scene were extracted and a total of 1904 chromaticity coordinates and correlated color temperatures (CCTs) derived. Maximum differences in chromaticities over spheres and over scenes were similar. When data were pooled over scenes, CCTs ranged from 3000 K to 20,000 K, a variation of the same order of magnitude as that occurring over the day. Any mechanisms that underlie stable surface color perception in natural scenes need to accommodate these large spatial variations in local illumination color.
Centre of Physics, Gualtar Campus, University of Minho, 4710-057 Braga, Portugal. Electronic address: smcn@fisica.uminho.pt.
Sérgio M C
SM
Nascimento
School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, UK. Electronic address: k.amano@manchester.ac.uk.
Kinjiro
K
Amano
School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, UK. Electronic address: d.h.foster@manchester.ac.uk.
David H
DH
Foster
D055253:Color Vision / Q000502:physiology*; D006801:Humans; D008027:Light; D008029:Lighting; D014796:Visual Perception / Q000502:physiology*
Color constancy; Color vision; Correlated color temperature; Hyperspectral imaging; Illumination variation; Natural scenes