Medial lines by parallelwise erosion of successive contour pairs

An iterated parallel thinning algorithm, using 3×3 local operations, is presented. Every iteration is split into four subiterations, each allowing pixel removal from two directions simultaneously. At each iteration, a layer of the pattern, characterized by nearly constant thickness in the Euclidean sense, is possibly removed. Consequently, the pattern is thinned down isotropically. Information regarding the local width of the pattern is also labeled on the pixels of the medial line