Quadtree Classification and TCQ Image Coding

The set partitioning in hierarchical trees (SPIHT) wavelet image coding algorithm can be interpreted as implicitly using classification in its bit-plane coding procedure. The source distribution induced by this classification is studied and rate-distortion performance is evaluated. A quadtree sorting procedure, similar to SPIHT, is used to explicitly form classes of wavelet coefficients. The classes are encoded using arithmetic and trellis-coded quantization. The resulting encoding algorithm offers consistent improvement over SPIHT performance due to the granular gain of the trellis code.