Singularities and regularities on line pictures via symmetrical trapezoids

An algorithm that decomposes a line image into singular and regular regions is presented. We define a contour trapezoid as the building block of regular regions, and postulate a maximal trapezoid set as the core of regular regions. Then, we describe an algorithm that calculates a maximal trapezoid set of a polygon and show how to use it to find a skeleton of a polygonal approximation of a contour. Experiments are explained to show the behavior of the new concept on real images as compared to previous algorithms.