Finding gray-skeletons by iterated pixel removal

The grey-skeleton is understood as a connected subset of a grey-scale pattern, which is a stylized version consisting of a network of digital lines centrally placed along local higher intensity regions. We present a parallel thinning algorithm that relies on the iterated erosion of the pattern, and which proceeds from lower grey values towards higher ones until the grey-skeleton is finally obtained. The process includes a preliminary phase in which the significance of the hollows and plateaux possibly existing in the pattern is investigated. In particular, the hollows with a significant depth are regarded as topological constraints for the skeleton structure.