Abstract: The influence of sensory processes on perception of pictures has long interested graphics scientists and engineers. Adaptation, illumination, and surround variables affect chromatic and achromatic apparent contrast and other aspects of color appearance. My recent experiments on apparent surface colors in complex patterns have led to a model of surface appearance in which early visual processes (e.g., adaptation, contrast) are only the first stage. Their role in surface perception is to relatively accurately encode the physical contrasts in the retinal image. Higher-order processes then compute surface properties from these contrast signals. It is, however, well known from neurophysiological and psychophysical measurements that early processed only approximate ideal encoding of image contrasts. Constant response amplitudes require larger luminance contrasts at low mean luminances. I have recently measured local apparent contrasts, lightnesses (apparent reflectances), and brightnesses (apparent luminances) in complex patterns at a variety of luminances that occur frequently in modern display devices. Apparent contrast decreased at low luminances, but this did not distort apparent reflectances (as one might expect from a number of recent lightness models). These results have several interesting implications for imaging applications.!
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