A vector quantizer with short-time memory for digital image coding

The authors propose a novel scheme of vector quantization with memory, named vector quantization with short-time memory (VQ-STM). The VQ-STM has two types of codebooks, a fixed-structure codebook whose codewords are kept unchanged, and a variable-structure codebook, which is defined as a subset of the fixed-structure codebook and whose structure is continually updated depending on the past behavior of the coder. The VQ-STM coder chooses the proper codebook between two codebooks for every input vector. The update of the variable-structure codebook is easily performed only by simple heuristics for maintaining a finite-length self-organizing sequential list which stores past coder outputs. The results of experimental simulations conducted on monochrome images demonstrate that significant compression gains can be achieved by enhancing the vector-quantization approach with the concept of short-time memory.<>