Parallel reduction operators for gray-tone pictures

Reduction operators iteratively applied to gray-tone pictures cause dilatio n of the regions, the gray-value of which is locally minimal, so that a gra y-tone picture with no distinction between foreground and background is tra nsformed into a set of bottom regions separated by ridge lines. The set of ridge lines can be understood as the skeleton of what is perceived as foreg round. We describe a two-subiteration parallel skeletonization algorithm em ploying new reduction operators which are based on the nonridge point condi tion and are topology preserving. The performance of the algorithm is discu ssed, in particular with respect to certain critical configurations, and ex perimental work is reported to evaluate the thinning capability of the prop osed reduction operators.