A tree-structured VQ (vector quantizer) that performs the nearest-neighbor encoding based on a locally optimal codebook generated by the algorithm of Y. Linde, A. Buzo and R.M. Gray (1980) is proposed. A design method is given to organize the code words by a quasi-voronoi tree. This tree structure allows the nearest-neighbor encoding without an exhaustive search. For a codebook of size K, encoding an input vector takes an expected number of O(log K) distortion evaluations for dimensionalities below eight; that time complexity is O(K/sup 1/2/) in practice for higher dimensionalities. The tree-structured VQ achieves a good compromise between optimality and encoding speed.
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