Segmentation of planar objects and their shadows in motion sequences

We investigate segmentation of planar objects and their cast shadows in image sequences. Given two moving image regions in an image sequence we present an algorithm for determining if the two moving regions can be interpreted as a planar object and its cast shadow. Projective geometry and motion properties are employed to directly recover a homology that constrains point correspondences of the outlines of the image regions and determine if they obey an object/shadow relationship. This homology is derived directly from the motions of the regions and therefore is easier to accomplish than determining point-to-point correspondences between candidate object-shadow pairs. Several experiments under approximate point light source illumination are presented.