An improved method to compute the convex hull of a shape in a binary image

A simple method for obtaining the convex hull of a shape, which generates an octagonal approximation, is based on repeatedly filling the central pixel in all 3 x 3 neighborhoods which show a concavity. We propose an extension of this technique that uses larger windows and yields improved results. The performance of our method is demonstrated both on specially generated objects (simulations) as well as on shapes obtained from ultrasound images of ovarian cysts. (C) 1997 Pattern Recognition Society. Published by Elsevier Science Ltd.