Method for adaptively compressing residual digital image data in a DPCM compression system

A block adaptive differential pulse code modulation (DPCM) system for transmitting or storing a digital image signal, a compressor for compressing the digital image by operating on n.times.m blocks of pixel values, comprising:

• a. a first numerically lossless DPCM processor responsive to blocks of pixel values for producing encoder command signals;
• b. a first lossy DPCM compressor responsive to blocks of pixel values for producing encoder command signals;
• c. an encoder for receiving encoder command signals and producing a compressed encoded bit stream;
• d. a switch responsive to a compression configuration mode signal and to the encoder command signals from the lossy compressor for selectively passing the encoder command signals from the numerically lossless processor or the lossy compressor to the encoder;
• and
• e. a second numerically lossless DPCM processor employing a different numerically lossless DPCM processing technique than the first numerically lossless DPCM processor for producing encoder command signals, the switch selectively passing the encoder command signals from the second numerically lossless DPCM processor to the encoder in response to the compression configuration mode signal.

A block adaptive differential pulse code modulation (DPCM) system for transmitting or storing a digital image signal, a compressor for compressing the digital image by operating on n.times.m blocks of pixel values, comprising:

• a. a first numerically lossless DPCM processor responsive to blocks of pixel values for producing encoder command signals;
• b. a first lossy DPCM compressor responsive to blocks of pixel values for producing encoder command signals;
• c. an encoder for receiving encoder command signals and producing a compressed encoded bit stream;
• d. a switch responsive to a compression configuration mode signal and to the encoder command signals from the lossy compressor for selectively passing the encoder command signals from the numerically lossless processor or the lossy compressor to the encoder;
• and
• e. wherein the first lossless DPCM processor includes:
• i. a predictor for receiving a pixel value and previously reconstructed pixel values and producing a predicted pixel value;
• ii. a subtractor for subtracting the predicted pixel value from the pixel value to produce a difference pixel value;
• iii. a symbolizer for generating a lossless symbol value corresponding to the difference pixel value;
• iv. a classifier for receiving the lossless symbol value and producing corresponding prefix and code signals;
• and
• v. a range select module for receiving a block of prefix signals and generating a range value for the block.

A block adaptive differential pulse code modulation (DPCM) system for transmitting or storing a digital image signal, a compressor for compressing the digital image by operating on n.times.m blocks of pixel values, comprising:

• a. a first numerically lossless DPCM processor responsive to blocks of pixel values for producing encoder command signals;
• b. a first lossy DPCM compressor responsive to blocks of pixel values for producing encoder command signals;
• c. an encoder for receiving encoder command signals and producing a compressed encoded bit stream;
• d. a switch responsive to a compression configuration mode signal and to the encoder command signals from the lossy compressor for selectively passing the encoder command signals from the numerically lossless processor or the lossy compressor to the encoder;
• and
• e. wherein the lossy compressor comprises:
• i. a predictor for receiving a pixel value and previously reconstructed pixel values and producing a predicted pixel value;
• ii. a subtractor for subtracting the predicted pixel value from the pixel value to produce a difference pixel value;
• iii. run select means for receiving a block of pixel values, reconstructed pixel values and a quantizer select signal, and producing a DC track signal representing an offset for the block of pixel values, a track flag indicating whether the block of pixel values is to be DC tracked, and a run flag indicating whether the block of pixel values is classified as a run block;
• iv. quantizer select means responsive to difference pixel values, and the run flag, for forming a corresponding block of difference pixel values and for producing the quantizer select signal for the block;
• v. a subsample mask responsive to the quantizer select signal for producing a binary mask;
• vi. a quantizer module responsive to the quantizer select signal, the binary mask, the DC track flag, the DC track signal and a second difference signal for producing quantized difference pixel values for each pixel within the block and corresponding symbol values;
• vii. a second predictor responsive to reconstructed pixel values from a current line and a previous line of pixels to produce a second predicted pixel value;
• viii. means for summing the second predicted pixel value and the corresponding quantized difference pixel value to produce the reconstructed pixel value;
• and
• ix. means for subtracting the second predicted pixel value from the pixel value to produce the second difference pixel value.

A block adaptive differential pulse code modulation (DPCM) system for transmitting or storing a digital image signal, a compressor for compressing the digital image by operating on n.times.m blocks of pixel values, comprising:

• a. a first numerically lossless DPCM processor responsive to blocks of pixel values for producing encoder command signals;
• b. a first lossy DPCM compressor responsive to blocks of pixel values for producing encoder command signals;
• c. an encoder for receiving encoder command signals and producing a compressed encoded bit stream;
• d. a switch responsive to a compression configuration mode signal and to the encoder command signals from the lossy compressor for selectively passing the encoder command signals from the numerically lossless processor or the lossy compressor to the encoder;
• and
• e. wherein the lossy compressor further comprises means for detecting low activity regions in the digital image signal and for generating an encoder command signal instructing the encoder to employ run length coding for the low activity region.

In a block adaptive differential pulse code modulation (DPCM) system for transmitting or storing a digital image signal, a decompressor for reconstructing a digital image from a compressed encoded bit stream produced by a compressor of the type having a first numerically lossless DPCM processor responsive to blocks of pixel values for producing encoder command signals;

• a first lossy DPCM compressor responsive to blocks of pixel values for producing encoder command signals;
• an encoder for receiving encoder command signals and producing a compressed encoded bit stream;
• and a switch responsive to a compression configuration mode signal and to the encoder command signals from the lossy compressor for selectively passing the encoder command signals from the numerically lossless processor or the lossy compressor to the encoder, comprising:
• a. a decoder for receiving the compressed encoded bit stream and reproducing the encoder command signals and the compression configuration mode signal;
• and
• b. reconstructing means responsive to the reproduced encoder command signals and the compression configuration mode signal for reconstructing the digital image, the reconstructing means including a first means for reconstructing lossless processed digital image data and a second means for reconstructing lossy compressed digital image data.

In a block adaptive differential pulse code modulation (DPCM) system, a lossless DPCM processor for compressing a digital image signal having pixel values, comprising:

• a. a predictor for receiving a pixel value and previously reconstructed pixel values and producing a predicted pixel value;
• b. a subtractor for subtracting the predicted pixel value from the pixel value to produce a difference pixel value;
• c. a symbolizer responsive to the predicted pixel value and the corresponding difference pixel value for generating a lossless symbol value corresponding to the difference pixel value;
• d. a classifier responsive to the lossless symbol value and producing corresponding prefix and code signals;
• e. a range select module for receiving a block of prefix signals and generating a range value for the block;
• and
• f. an encoder responsive to the prefix, code and range values for producing a compressed bit stream representing the digital image.

In a block adaptive differential pulse code modulation (DPCM) system, a lossy DPCM compressor for compressing a digital image signal having pixel values, comprising:

• a. a predictor for receiving a pixel value and previously reconstructed pixel values and producing a predicted pixel value;
• b. a subtractor for subtracting the predicted pixel value from the pixel value to produce a difference pixel value;
• c. run select means for receiving a block of pixel values, reconstructed pixel values and a quantizer select signal, and producing a DC track signal representing an offset for the block of pixel values, a track flag indicating whether the block of pixel values is to be DC tracked, and a run flag indicating whether the block of pixel values is classified as a run block;
• d. quantizer select means responsive to difference pixel values, and the run flag, for forming a corresponding block of difference pixel values and for producing the quantizer select signal for the block;
• e. a subsample mask responsive to the quantizer select signal for producing a binary mask;
• f. a quantizer module responsive to the quantizer select signal, the binary mask, the DC track flag, the DC track signal and a second difference signal for producing quantized difference pixel values for each pixel within the block and corresponding symbol values;
• g. a second predictor responsive to reconstructed pixel values from a current line and a previous line of pixels to produce a second predicted pixel value;
• h. means for summing the second predicted pixel value and the corresponding quantized difference pixel value to produce the reconstructed pixel value;
• i. means for subtracting the second predicted pixel value from the pixel value to produce the second difference pixel value;
• and
• j. an encoder responsive to the quantizer select signal and the symbol value corresponding to the quantized difference pixel value for producing a compressed bit steam representing the digital image.