Using real shadows to create virtual ones

In Augmented Reality (AR) real imagery is superimposed by computer graphics renderings of virtual objects. This paper addresses the problem of creating the illusion that the virtual objects cast credible shadows in the real scenario. A step towards this is to be able to detect shadow regions in images of natural scenes, and this paper describes an approach to such shadow detection. The shadow detection can distinguish between directly fit areas, penumbra (half-shadow) areas, and umbra (full shadow) areas. Furthermore, it is demonstrated how virtual shadows can-be created which appear very similar to the real shadows.