Abstract: The influence of sensory processes on perception ofpictures has long interested graphics scientists andengineers. Adaptation, illumination, and surroundvariables affect chromatic and achromatic apparentcontrast and other aspects of color appearance. Myrecent experiments on apparent surface colors incomplex patterns have led to a model of surfaceappearance in which early visual processes (e.g.,adaptation, contrast) are only the first stage. Theirrole in surface perception is to relatively accuratelyencode the physical contrasts in the retinal image.Higher-order processes then compute surface propertiesfrom these contrast signals. It is, however, well knownfrom neurophysiological and psychophysical measurementsthat early processed only approximate ideal encoding ofimage contrasts. Constant response amplitudes requirelarger luminance contrasts at low mean luminances. Ihave recently measured local apparent contrasts,lightnesses (apparent reflectances), and brightnesses(apparent luminances) in complex patterns at a varietyof luminances that occur frequently in modern displaydevices. Apparent contrast decreased at low luminances,but this did not distort apparent reflectances (as onemight expect from a number of recent lightness models).These results have several interesting implications forimaging applications.!
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