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Device for encoding digital signals representing images, and corresponding decoding device

  • US 5,500,677 A
  • Filed: 06/07/1995
  • Issued: 03/19/1996
  • Est. Priority Date: 10/28/1992
  • Status: Expired due to Term
First Claim
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1. An encoding device for encoding a digital signal corresponding to images subdivided into blocks, comprising:

  • a discrete cosine transform circuit for processing a first digital signal to obtain first coefficients;

    a first quantizing circuit for quantizing the first coefficients to obtain first quantized values, said first quantizing circuit having a first quantization step;

    a first encoding circuit for encoding the first quantized values to obtain first encoded signals having a first quality level;

    a first inverse quantization circuit for dequantizing the first quantized values to obtain first dequantized coefficients;

    a first subtracter for subtracting the first dequantized coefficients from the first coefficients to obtain second coefficients;

    a second quantizing circuit provided in cascade with the first quantizing circuit for quantizing the second coefficients to obtain second quantized values, said second quantizing circuit having a second quantization step which is finer than the first quantization step;

    a second encoding circuit for encoding the second quantized values to obtain second encoded signals having a second quality level, which is higher than the first quality level;

    a second inverse quantization circuit for dequantizing the second quantized values to obtain second dequantized coefficients;

    a first adder circuit for adding the first dequantized coefficients and the second dequantized coefficients to obtain third coefficients;

    an inverse discrete cosine transform circuit for processing the third coefficients to obtain a third digital signal;

    a second adder circuit for adding the third digital signal and a predicted digital signal to obtain a fourth digital signal;

    a picture memory for storing and supplying the fourth digital signal;

    a motion compensation stage for operating on the fourth digital signal to produce the predicted digital signal; and

    a second subtracter circuit for subtracting the predicted digital signal from the digital signal to obtain the first digital signal.

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