Skeletal lines in gray-tone digital pictures

In a gray-tone digital picture, the skeleton is a set of digital lines mainly located in correspondence with the regions having locally higher gray-values. We describe a sequential skeletonization algorithm based on the dilation of the bottom regions, accomplished by an ordered propagation technique through increasing gray-levels. The non-bottom regions are eroded by lowering the gray-value of their pixels, except for those pixels playing the role of topographical feature points and destined to become skeletal pixels. The algorithm allows one to associate to each skeletal pixel also quantitative information related to the gray-values characterizing the nearby regions. The resulting skeleton is more suitable than others to undergo pruning, which is a postprocessing step necessary in most cases to create a set of perceptually significant skeletal lines