Can the Sun's Direction be Estimated from an Image Prior to the Computation of Object Shape?

Abstract

Various computational techniques have been developed that perform reasonably well in inferring shape from shading. However, these techniques typically require substantial prerequisite information if they are to evolve an estimate of surface shape. It is therefore interesting to consider how depth might be inferred from shading information without prior knowledge of various scene conditions. One approach has been to undertake a pre-processing step of estimating the light-source direction, thereby providing input to the computation of shape from shading. In this paper, we present evidence that a versatile light-source-direction estimator is unattainable, and propose that, in the absence of domain-specific knowledge, shape and light-source direction should be determined in a coupled manner.