Detection of curved and straight segments from gray-scale topography

Abstract

Conventional structural pattern recognition methods that rely on thinning approximate the skeleton by polygons and proceed from that step to recognition. Polygonal approximations have the disadvantage that they introduce significant ambiguities. In particular, vertices may correspond either to real corners or to approximations of smooth arcs. The method presented in this paper attempts to overcome the above problem by performing feature decomposition without doing polygonal approximations. The proposed method relies on topographic features and in particular ridge lines. Ridge lines are normally centered within character strokes, forming skeleton-like ribbons. The information about ridge line directions obtained from the underlying surface of the gray tone is used to discriminate between arcs and straight line segments. By not using a conventional thinning algorithm and the usual polygonal approximations, we are able to reduce some artifacts of conventional thinning and to eliminate completely the ambiguities mentioned above.