Can the Sun’s Direction Be Estimated Prior to the Determination of Shape? Wojciech Chojnacki

A smooth object depicted in a photographwill often exhibit brightness variation, or shading. 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 the 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 argue that a versatile light-source estimator of this kind is unattainable, and suggest that in the absence of domain-specific knowledge, shape and light-source direction must be determined in a coupled manner.