Fragment grouping via the principle of perceptual occlusion

Bounding contours of physical objects are often fragmented by other occluding objects. Long-distance perceptual grouping seeks to join fragments belonging to the same object. Approaches to grouping based on invariants assume objects are in restricted classes, while those based on minimal energy continuations assume a shape for the missing contours and require this shape to drive the grouping process. We propose the more general principle that those fragments should be grouped whose fragmentation could have arisen from a generic occluder. The gap skeleton is introduced as a representation of this virtual occluder, and an algorithm for computing it is given.