On Consistent Discrimination between Directed and Diffuse Outdoor Illumination

This investigation studies the contrast across boundaries of shadows which are cast by moving vehicles or selected stationary objects in a traffic scene onto the road surface. If a sufficient fraction of this subset of hypothetical shadow contours is overlapped by strong edge elements, such a finding is usually taken as a cue that directed sunshine illuminates the traffic scene. Otherwise, diffuse illumination is assumed. Experiments with different illumination states of a traffic scene indicate that such a conclusion appears justified in many cases. It is demonstrated, however, that much more complicated situations may occur which need detailed inferences in order to arrive at a consistent interpretation.