Edgel aggregation and edge description

Abstract An edge in an image corresponds to a discontinuity in the intensity surface of the underlying scene. It can be approximated by a piecewise straight curve composed of edgels, i.e., short, linear edge elements, each characterized by a direction and a position. A substantial effort has been previously directed towards edgel detection. Edgels, by themselves, are of little use in vision systems. In this paper we discuss algorithms to aggregate edgels into edges and to describe these edges by best-fit curves. The edgel-linking algorithm is simple and has a local character. It relies only on edgel proximity and direction. The basis used for edge description consists of conic sections. Position and tangent continuity are preserved in the curve-fitting stage. The problems addressed include, the discovery of straight lines and their discrimination from low-curvature segments, the detection of corners, the choice of knots, and the estimation of the distance of an edgel from a conic section. We demonstrate our algorithms with a detailed example.

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