Contour fragment grouping and shared, simple occluders

Bounding contours of physical objects are often fragmented by other occludi ng objects. Long-distance perceptual grouping seeks to join fragments belon ging to the same object. Approaches to grouping based on invariants assume objects are in restricted classes, while those based on minimal energy cont inuations assume a shape for the missing contours and require this shape to drive the grouping process. While these assumptions may be appropriate for certain specific tasks or when contour gaps are small, in general occlusio n can give rise to large gaps, and thus long-distance contour fragment grou ping is a different type of perceptual organization problem. We propose the long-distance principle that those fragments should be grouped whose fragm entation could have arisen from a shared, simple occluder. The gap skeleton is introduced as a representation of this virtual occluder, and an algorit hm for computing it is given. Finally, we show that a view of the virtual o ccluder as a disk can be interpreted as an equivalence class of curves inte rpolating the fragment endpoints. (C) 1999 Academic Press.