Yoshiyuki Okuyama

A high-speed labeling algorithm for raster-scanned type

Labeling is a procedure by which labels are assigned separately to a number of connected components, and it is also one of the important functions in the image processing system. In the conventional raster-scanned labeling, labels are assigned temporarily in a small local area. Then a large number of temporary labels (pairs of connected labels) is generated for the same connected component, and a long processing time is required to unify and transform them into the final label. From such a viewpoint, this paper discusses the reduction of processing time for the unification of pairs of connected labels. As a result, it is concluded that the following two approaches are effective: 1 Simplify the table structure for storing the pairs of connected labels 2 Reduce the generation of the pairs of connected labels. The following MIN-MAX method is devised as a means to realize (1). In the table storing the pairs of connected labels, MAX of the two temporary labels forming the pair of connected labels is adopted as the address, and MIN is used as the content data. To realize (2), it is noted that the concave and indented connected components often produce the pair of connected labels. The pixel-embedding and the forward pixel referring methods are devised for such situations. This paper presents the algorithms for those methods, and reports on the result of evaluation.