Fu Chang, Ya-Ching Lu and Theo Pavlidis
In this article, we propose a new thinning algorithm based on line sweep operation. A line sweep is a process where the plane figure is divided into parallel slabs by lines passing through certain "events" and items are then processed according to an order of the slabs. Assuming that the contour of the figure to be thinned have been approximated by polygons, the "events" are then the vertices of the polygons and the line sweep algorithm looks for pairs of edges that lie within each slab.
The pairing of edges are useful for detecting both regular and intersection regions. The regular regions can be found at the site where pairings between edges exist. Intersection regions, on the other hand, are where such relations would cease to exist, due to the fact that pair relations between edges of wide distance were canceled. A salient feature of our approach is to find simultaneously the set of regular regions that attach to the same intersection region. Such a set is thus called an intersection set.
The output of our algorithm consists of skeletons as well as intersection sets. Both of them can be used as features for subsequent character recognition. Moreover, the line sweep thinning algorithm is efficient in computation as compared with a pixelbased thinning algorithm which outputs skeletons only.