A simple recursive method for converting a chain code into a quadtree with a lookup table

Abstract

We present a simple recursive method for converting a chain code into a quadtree. We generate the quadtree black nodes level by level, starting from the finest resolution (i.e. the bottom) level toward the coarsest resolution (i.e. the top) level. Meanwhile, at each resolution level a new object border is revealed after the removal of the black nodes. The chain code elements for this new object border can be easily generated. Thus, the quadtree black nodes and the chain code elements of the new object border are generated side by side and their generations constitute a basic cycle of the conversion process. We show the generations can be done with the aid of a lookup table. Finally, we compare our method with the existing two-phase methods exemplified by Samet's method in terms of the total numbers of major operations including node allocations, node color filling, and node pointer linking. It indicates that our method is conceptually simpler and runs faster. (C) 2001 Elsevier Science B.V. All rights reserved.