Parallel processing of image contours

Abstract

This paper describes a parallel algorithm for ranking the pixels on a curve in O(log N) time using an EREW PRAM model. The algorithms accomplish this with N processors for a (root)N X (root)N image. After applying such an algorithm to an image, we are able to move the pixels from a curve into processors having consecutive addresses. This is important on hypercube connected machines like the Connection Machine because we can subsequently apply many algorithms to the curve using powerful segmented scan operations (i.e., parallel prefix operations). We shall illustrate this by first showing how we can find piecewise linear approximations of curves using Ramer's algorithm. This process has the effect of converting closed curves into simple polygons. As another example, we shall describe a more complicated parallel algorithm for computing the visibility graph of a simple planar polygon. The algorithm accomplishes this in O(k log N) time using O(N2/log N) processors for an N vertex polygon, where k is the link-diameter of the polygon in consideration. Both of these algorithms require only scan operations (as well as local neighbor communication) as the means of inter-processor communication. Thus, the algorithms can not only be implemented on an EREW PRAM, but also on a hypercube connected parallel machine, which is a more practical machine model. All these algorithms were implemented on the Connection Machine, and various performance tests were conducted.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.