Memory efficient propagation-based watershed and influence zone algorithms for large images

Propagation front or grassfire methods are very popular in image processing because of their efficiency and because of their inherent geodesic nature. However, because of their randomaccess nature, they are inefficient in large images that cannot fit in available random access memory. In this paper, we explore ways to increase the memory efficiency of two algorithms that use propagation fronts: the skeletonization by influence zones and the watershed transform. Two algorithms are presented for the skeletonization by influence zones. The first computes the skeletonization on surfaces without storing the enclosing volume. The second performs the skeletonization without any region reference, by using only the propagation fronts. The watershed transform algorithm that was developed keeps in memory the propagation fronts and only one greylevel of the image. All three algorithms use much less memory than the ones presented in the literature so far. Several techniques have been developed in this work in order to minimize the effect of these set operations. These include fast search methods, double propagation fronts, directional propagation, and others.