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Image compression method and apparatus employing distortion adaptive tree search vector quantization with avoidance of transmission of redundant image data

  • US 5,247,357 A
  • Filed: 11/19/1991
  • Issued: 09/21/1993
  • Est. Priority Date: 05/31/1989
  • Status: Expired due to Term
First Claim
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1. In a Vector quantization encoder of the type that employs a tree structured codebook to vector quantize input vectors and sequentially transmits vector quantized data for input vectors to a remote decoder for reconstructing a substantial representation of each input vector therefrom, the codebook having plural levels of codevectors, each codevector being representative of a possible input vector and there being an identification (ID) code associated with each codevector, the codevectors at each successive level representing possible input vectors with greater accuracy than codevectors at a preceding level, a method comprising the steps of:

  • a) comparing a representation of a previous input vector that has already been vector quantized to a current input vector to obtain a first measure of difference between the representation of the previous input vector and the current input vector;

    b) transmitting to the decoder an instruction to reconstruct a substantial representation of the current input vector from vector quantized data already stored in the decoder for the previous input vector only when the first measure of difference is less than a threshold value, but otherwise performing the following steps for the current input vector;

    c) processing the current input vector and selecting an initial level of the codebook;

    d) comparing the processed input vector to the codevectors at the selected level of the codebook and selecting the codevector that most closely resembles the processed input vector;

    e) obtaining a second measure of difference between the processed input vector and the selected codevector;

    f) transmitting an indication of the ID code associated with the selected codevector only if the second measure of difference is less than the threshold value, but otherwise selecting a next level of the codebook and repeating steps (d) and (e) until either the second measure of difference is less than the threshold value or a last level of the codebook has been employed, then transmitting the indication of the ID code associated with the finally selected codevector, the transmitted indication being the vector quantized data for the current input vector;

    wherein vector quantized data for the current input vector need not be transmitted to reconstruct a representation of the current input vector at the decoder when the first measure of difference is less than the threshold value.

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