COLOR AND LUMINANCE INFORMATION IN NATURAL SCENES

The spatial filtering applied by the human visual system appears to be low pass for chromatic stimuli and band pass for luminance stimuli. H ere we explore whether this observed difference in contrast sensitivit y reflects a real difference in the components of chrominance and lumi nance in natural scenes. For this purpose a digital set of 29 hyperspe ctral images of natural scenes was acquired and its spatial frequency content analyzed in terms of chrominance and luminance defined accordi ng to existing models of the human cone responses and visual signal pr ocessing. The statistical 1/f amplitude spatial-frequency distribution is confirmed for a variety of chromatic conditions across the visible spectrum. Our analysis suggests that natural scenes are relatively ri ch in high-spatial-frequency chrominance information that does not app ear to be transmitted by the human visual system. This result is unlik ely to have arisen from errors in the original measurements. Several r easons may combine to explain a failure to transmit high-spatial-frequ ency chrominance: (a) its minor importance for primate visual tasks, ( b) its removal by filtering applied to compensate for chromatic aberra tion of the eye's optics, and (c) a biological bottleneck blocking its transmission. In addition, we graphically compare the ratios of lumin ance to chrominance measured by our hyperspectral camera and those mea sured psychophysically over an equivalent spatial-frequency range. (C) 1998 Optical Society of America.