An asynchronous thinning algorithm

A problem common to many areas of pictorial information processing is the transformation of a bilevel (two-color) image into a line drawing. The first step in such a process is discussed: transformation of the bilevel image into another bilevel image that is “thin.” An algorithm is proposed that can be implemented in either parallel or sequential fashion, and therefore is suitable for a mixed operation where a group of processors operate in parallel with each one examining sequentially the pixels of a part of the image assigned to it. It is possible to process images in pieces and thin correctly parts that are intersected by the dividing lines. Therefore, the method can be used on large images, such as maps and engineering drawings. The algorithm may also be run with certain options that label the thinned image so that exact reconstruction of the original is possible.