Very-low-bit-rate video coding using quadtree decomposition and cache-based vector quantization

We investigate the use of vector quantizers (VQs) with memory to encode image sequences. A video coding technique using cache-based vector quantization is presented. In this technique, a small codebook (subcodebook), meaning a cache memory codebook, is used to encode the input signals. This small subcodebook is dynamically generated from a much larger codebook (supercodebook) through a caching scheme. Therefore, the subcodebook dynamically adapts to the local characteristics of the motion-compensated residual signal, which varies with time. Both "least recently used" (LRU) and modified LRU cache-replacement techniques are used. An efficient bit-allocation strategy using quadtree decomposition is used with the cache-based VQ to compress the video signal. The proposed video codec outperforms H.263 in terms of PSNR and perceptual quality at very low bit rates, ranging from 5 to 15 kbps. Experimental results are presented for two image sequences, "salesman" and "Miss America".