Rate-distortion optimization for tree-structured source coding with multi-way node decisions

A new algorithm is proposed for the generation of rate-distortion optimized tree-structures used in source coding. The algorithm solves a more general problem than that assumed for a previous method by P.A. Chou et al. (1989). It arises when the tree structure is to be optimized with a multi-way decision made at each leaf node. The simplifying assumption that the three structure performance functions are monotone with respect to the level of nodes in the tree is also removed. Two applications of the more general problem in image/video compression are quadtree coding with vector quantization and variable block-size motion compensation. This new method is not a pruning algorithm, as the optimal trees may not be nested. The new algorithm finds the global optimal tree structure and node decisions in the unconstrained rate allocation sense