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Abstract

The human visual system has a remarkable ability to interpret smooth patterns of light and shade on a surface in terms of 3-D surface geometry. Classical studies of shape-from-shading have assumed that surface luminance depends on the local surface orientation. This classical shading model holds, for example, on a sunny day. A common
situation in which the classical model fails to hold, however, is a diffuse lighting condition such as on a cloudy day. Here we report on the first set of psychophysical experiments that explicitly address
perception of shape-from-shading under diffuse lighting. Our main findings are that depth discrimination under diffuse lighting is superior to that predicted by a classical sunny day model, and by a model in which depth varies with perceived luminance i.e. dark means deep. We find that performance is correlated with the latter model,
however, under both diffuse source and point source lighting. The results imply that the visual system uses multiple models when perceiving shape-from-shading.