A finite-state vector quantizer for low-rate image sequence coding

Vector quantization (VQ) is an effective spatial domain image coding technique at under 1.0 bits per pixel (bpp). Its performance can be improved by incorporating block-to-block memory. Finite State VQs (FSVQ) do this by using a state variable to express characteristics of neighboring blocks and identify which subset of a supercodebook the FSVQ encoder and decoder are to use for the current vector. This paper describes a new method for image sequence coding that uses an interframe FSVQ In the spatial domain. Block-to-block and frame-to-frame memory is expressed through a state which is a function of block motion and the intensity gradients of a block's neighbors. A scalar predictor adds additional interframe memory and reduces the energy of residuals encoded by the VQ, improving edge rendition and limiting blocking artifacts. The codec at 0.6 bpp outperforms a similar, non-finite state intraframe VQ at 1.0 bpp. No motion compensation or conditional replenishment is used.