Unbalanced tree structure for frame adaptive vector quantization of image sequences
Fabio Lavagetto, Sandro Zappatore · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1990
In this paper a coding technique is presented which extends the methodology of vector quantization to image sequence coding. The devised algorithm basically consists of a processing stage encharged to build up the initial codebook and a codebook updating mechanism running on-line with the coding phase, to adaptively track the varying statistics of the incoming images. The codebook is organized in a binary tree structure where each leaf represents a reproduction vector. The tree grows intrinsecally unbalanced in the sense that each node splits or not according to the intensity statistics of the vector population which refers to it. By doing so, the suboptimality of tree structured vector quantization with respect to full search approaches is successfully overcome. During the coding phase the unbalanced tree is left free to plastically track the temporal variations of the incoming data statistics. This results either in some reproduction vectors to be replaced by new ones, or in some changes in the tree topology to be carried out, typically a leaf which needs to split or two leaves which, conversely, shall be cut off. An updating code stream is periodically delivered onto the channel, interlaced with coding data, to replenish the reconstruction codebook. Application to videotelephone sequences has given promising preliminary results which are presented and discussed.