Edge Linking Using Thresholding

Edge detection followed by thinning produces a set of points which lie along edges in the original image. It is important to link together the pixels which lie along the same edge. The resulting associated groups can then be fitted with line segments. This paper presents a new technique for this edge point linking problem. Each edge point is linked to its appropriate neighbor on either side by considering those contours, produced by thresholding, which pass through the given edge point. For each such contour, the edge point nearest the given edge point along the contour (in, say, the clockwise direction) is recorded. The edge point occurring most often as an associate across the set of gray level thresholds, is chosen as the clockwise associate. A figure of merit based on path length and straightness is used to break any ties. The counterclockwise neighbor is chosen similarly. Two points which are mutual associates denote a symmetric link. If all non-symmetric links are deleted, the resulting structure is a set of linear chains of nodes called 'symchains' It is claimed that symchains provide a rich edge structure for further processing.