Device for encoding digital signals representing images, and corresponding decoding device
First Claim
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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Abstract
A device for encoding digital signals corresponding to images which are subdivided into blocks has a first encoding channel including a discrete cosine transform circuit. In addition to this first encoding channel the device has a second encoding channel which encodes the differences between the original coefficients present at the output of the discrete cosine transform circuit and the same coefficients after quantization and inverse quantization. This second channel encodes the differences after they are quantized with a finer quantization step than in the first encoding channel. The device further includes a prediction channel including a motion compensation stage, that uses both the inverse quantized coefficients coded in the first encoding channel and the inverse quantized coefficients coded in the second encoding channel to produce a predicted digital signal. This predicted digital signal is subtracted from the digital signal to be encoded by the device.
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Citations
4 Claims
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1. An encoding device for encoding a digital signal corresponding to images subdivided into blocks, comprising:
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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. - View Dependent Claims (2, 3, 4)
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Specification