Image compression system and method having optimized quantization tables
First Claim
1. A digital image compression preprocessor for use in a discrete cosine transform-based digital image compression device, the preprocessor comprising:
- (a) gathering means for determining discrete cosine transform statistics from input digital image data, wherein the discrete cosine transform statistics include counts related to the number of times each of a plurality of discrete cosine transform coefficients derived from the input digital image data takes a value;
(b) computing means, operatively coupled to the gathering means, for calculating an image distortion array and a rate of image compression array based upon the discrete cosine transform statistics for each of a plurality of possible quantization values; and
(c) quantization table generating means, operatively coupled to the computing means, for optimizing the rate of image compression array against the image distortion array to derive a rate-distortion-optimal quantization table.
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Abstract
A digital image compression preprocessor for use in a discrete cosine transform-based digital image compression device is provided. The preprocessor includes a gathering mechanism for determining discrete cosine transform statistics from input digital image data. A computing mechanism is operatively coupled to the gathering mechanism to calculate a image distortion array and a rate of image compression array based upon the discrete cosine transform statistics for each possible quantization value. A dynamic programming mechanism is operatively coupled to the computing mechanism to optimize the rate of image compression array against the image distortion array such that a rate-distortion-optimal quantization table is derived. In addition, a discrete cosine transform-based digital image compression device and a discrete cosine transform-based digital image compression and decompression system are provided. Also, a method for generating a rate-distortion-optimal quantization table, using discrete cosine transform-based digital image compression, and operating a discrete cosine transform-based digital image compression and decompression system are provided.
101 Citations
44 Claims
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1. A digital image compression preprocessor for use in a discrete cosine transform-based digital image compression device, the preprocessor comprising:
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(a) gathering means for determining discrete cosine transform statistics from input digital image data, wherein the discrete cosine transform statistics include counts related to the number of times each of a plurality of discrete cosine transform coefficients derived from the input digital image data takes a value; (b) computing means, operatively coupled to the gathering means, for calculating an image distortion array and a rate of image compression array based upon the discrete cosine transform statistics for each of a plurality of possible quantization values; and (c) quantization table generating means, operatively coupled to the computing means, for optimizing the rate of image compression array against the image distortion array to derive a rate-distortion-optimal quantization table. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A discrete cosine transform-based digital image compression device, comprising:
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(a) discrete cosine transformer means for dividing input digital image data into fixed length image blocks and generating a corresponding block of discrete cosine transform coefficients for each fixed length image block by applying a discrete cosine transform to each fixed length image block; (b) quantization table generator, operatively coupled to the discrete cosine transformer means, which generates a rate-distortion-optimal quantization table, comprising; (i) gathering means for determining discrete cosine transform statistics from each block of discrete cosine transform coefficients, wherein the discrete cosine transform statistics include counts related to the number of times each discrete cosine transform coefficient from the blocks takes a value; (ii) computing means, operatively coupled to the gathering means, for calculating an image distortion array and a rate of image compression array based upon the discrete cosine transform statistics for each of a plurality of possible quantization values; and (iii) quantization table generating means, operatively coupled to the computing means, for optimizing the rate of image compression array against the image distortion array to derive the rate-distortion-optimal quantization table; (c) quantizing means, operatively coupled to the discrete cosine transformer means and the quantization table generating means, for generating a corresponding block of quantized discrete cosine transform coefficients for each block of discrete cosine transform coefficients by quantizing each block of discrete cosine transform coefficients with the rate-distortion-optimal quantization table; and (d) entropy coding means, operatively coupled to the quantizing means, for entropy coding each block of quantized discrete cosine transform coefficients to form a corresponding compressed block such that a sequence of all of the compressed blocks forms the compressed digital image data. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A discrete cosine transform-based digital image compression and decompression system, comprising:
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(a) a transmitting device which receives input digital image data, generates compressed digital image data, and transmits the compressed digital image data and a rate-distortion-optimal quantization table over a communication channel, the transmitting device comprising; (i) discrete cosine transformer means for dividing the input digital image data into fixed length image blocks and generating a corresponding block of discrete cosine transform coefficients for each fixed length image block by applying a discrete cosine transform to each fixed length image block; (ii) quantization table generating means, operatively coupled to the discrete cosine transformer means, for generating the rate-distortion-optimal quantization table by determining discrete cosine transform statistics from each block of discrete cosine transform coefficients, wherein the discrete cosine transform statistics include counts related to the number of times each discrete cosine transform coefficient from the blocks takes a value, calculating an image distortion array and a rate of image compression array based upon the discrete cosine transform statistics for each of a plurality of possible quantization values, and optimizing the rate of image compression array against the image distortion array to derive the rate-distortion-optimal quantization table; (iii) quantization means, operatively coupled to the discrete cosine transformer means and the quantization table generating means, for generating a corresponding block of quantized discrete cosine transform coefficients for each block of discrete cosine transform coefficients by quantizing each block of discrete cosine transform coefficients with the rate-distortion-optimal quantization table; and (iv) entropy coding means, operatively coupled to the quantizing means, for entropy coding each block of quantized discrete cosine transform coefficients to form a corresponding compressed block such that a sequence of all of the compressed blocks forms the compressed digital image data; and (b) a receiving device which receives the compressed digital image data and the rate-distortion-optimal quantization table from the communication channel and generates decompressed digital image data, the receiving device comprising; (i) decoding means for decoding each entropy-coded compressed block in the received compressed digital image data into a corresponding block of quantized discrete cosine transform coefficients; (ii) dequantizing means, operatively coupled to the decoding means, for generating a corresponding block of discrete cosine transform coefficients for each block of quantized discrete cosine transform coefficients based on the received rate-distortion-optimal quantization table; and (iii) inverse discrete cosine transformer means, operatively coupled to the dequantizing means, for generating a corresponding decompressed block of fixed length digital image data for each block of discrete cosine transform coefficients by applying an inverse discrete cosine transform to each block of discrete cosine transform coefficients such that a sequence of all of the decompressed blocks forms the decompressed digital image data. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31)
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32. A method for generating a rate-distortion-optimal quantization table for use in a discrete cosine transform-based digital image compression process, the method comprising the steps of:
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(a) determining discrete cosine transform statistics from input digital image data, wherein the discrete cosine transform statistics include counts related to the number of times each of a plurality of discrete cosine transform coefficients derived from the input digital image data takes a value; (b) calculating an image distortion array and a rate of image compression array based upon the discrete cosine transform statistics for each of a plurality of possible quantization values; and (c) optimizing the rate of image compression array against the image distortion array to derive the rate-distortion-optimal quantization table. - View Dependent Claims (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44)
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Specification