Estimating Sun Direction from a Single Image

This paper focusses on the pioneering and influential method of Pentland which automatically estimates the direction of the “sun” from a single image. We show that, under the assumptions used in the derivation of the method, the estimate of source direction is incorrect. Specifically, we show that an image-based expression used in calculating source direction diverges to infinity as the density of image points is increased, and that, as a result, the formula involving this expression is incorrect. Supporting experimental evidence is given. We propose an alternative source estimator which is free of these drawbacks.