Skeletons from chain-coded contours

The speed of skeletonizing algorithms is improved by applying them on contour pixels only. Further improvement can be gained by using chain-coded contours. If the deletion of a contour pixel is allowed, according to a simple connectivity test, the corresponding pair of chain codes is replaced by a predefined test of other chain codes. The resulting skeleton does not require cleaning or pruning, but the number of branches can be easily controlled by modifying the replacement table. Since the algorithm is sequential, the starting pixel on the contour requires special attention to avoid spurious branches