Method for decompressing JPEG files using a variable block size inverse discrete cosine transform

• US 6,778,707 B1
• Filed: 12/17/1999
• Issued: 08/17/2004
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: de Queiroz, Ricardo L.
• Primary Examiner(s): Mehta, Bhavesh M.
• Assistant Examiner(s): Bayat, Ali
• Application Number:
  US09/466,567
• Time in Patent Office: 1,705 Days
• Field of Search: 382/232, 382/233, 382/239, 382/248, 382/250, 382/251, 382/235, 382/260, 358/426.02, 358/426.04, 358/426.16, 375/240.02, 375/240.18, 375/240.2
• US Class Current: 382/233
• CPC Class Codes: H04N 19/122 Selection of transform size, e.g. 8x8 or 2x4x8 DCT; Selection of sub-band transforms of varying structure or type
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/60 using transform coding

Abstract

A method for decompressing digital image data to improve the speed of decompression is disclosed. More specifically, the present invention improves image decompression time by operating upon a subset of the original data and by performing a modified discrete cosine transform on a subset of the originally provided data. The subset is determined by examining the compressed data and looking for a particular pattern of zero values and/or and “end of block” statement.

Claims

1. A method of improving the speed and efficiency of electronic data decompression, comprising:

retrieving compressed serial data corresponding to a matrix;

examining the compressed serial data for a zero coefficient position;

selecting a transform as based upon the zero coefficient position found in the examining step;

applying the selected transform to a subset of the compressed serial data to produce a subset transform result; and

interpolating the subset transform result to provide decompressed data.

2. The method of claim 1 wherein the step of applying a transform includes using an inverse discrete cosine transform.

3. The method of claim 1 wherein the step of applying a transform includes using a 1×

1 inverse discrete cosine transform.

4. The method of claim 1 wherein the step of applying a transform includes using a 2×

2 inverse discrete cosine transform.

5. The method of claim 4 wherein the step of interpolating involves multiplying by a factor of 0.25 for scaling.

6. The method of claim 1 wherein the step of applying a transform includes using a 4×

4 inverse discrete cosine transform.

7. The method of claim 6 wherein the step of interpolating involves multiplying by a factor of 0.50 for scaling.

8. The method of claim 1 wherein the step of interpolating involves scaling.

9. A method of improving the speed and efficiency of electronic data decompression, comprising:

examining compressed serial data for the position of an end-of-block command in the data;

selecting an inverse transform depending upon the position of an end-of-block command found in the examining step, applying the selected inverse transform to the compressed data to produce a transform result; and

interpolating the transform result to provide decompressed data.

10. The method of claim 9 wherein the step of examining for particular arrangements of data comprises determining the location of zero values in the compressed serial data.

11. The method of claim 10 wherein the step of applying a transform includes using a 1×

1 inverse discrete cosine transform.

12. The method of claim 10 wherein the step of applying a transform includes using a 2×

2 inverse discrete cosine transform.

13. The method of claim 10 wherein the step of applying a transform includes using a 4×

4 inverse discrete cosine transform.

14. The method of claim 9 wherein the step of examining for particular arrangements of data comprises determining the location of a zero coefficient in the compressed serial data.

15. The method of claim 14 wherein the step of applying a transform includes using a 1×

1 inverse discrete cosine transform.

16. The method of claim 14 wherein the step of applying a transform includes using a 2×

2 inverse discrete cosine transform.

17. The method of claim 14 wherein the step of applying a transform includes using a 4×

4 inverse discrete cosine transform.

18. A method of improving the speed and efficiency of JPEG decompression, comprising:

examining compressed serial data for a zero coefficient position to determine a determined subset of compressed data;

selecting an inverse transform depending upon the zero coefficient position found in the examining step;

applying the selected inverse transform to the determined subset of compressed data to produce a subset transform result; and

interpolating the subset transform result to provide a full 8×

8 matrix of pixel data.

19. The method of claim 18 wherein the step of examining for particular arrangements of data comprises determining the location of zero values in the compressed serial data.

20. The method of claim 19 wherein the step of applying a transform includes using a 1×

1 inverse discrete cosine transform.

21. The method of claim 19 wherein the step of applying a transform includes using a 2×

2 inverse discrete cosine transform.

22. The method of claim 19 wherein the step of applying a transform includes using a 4×

4 inverse discrete cosine transform.

23. The method of claim 18 wherein the step of examining for particular arrangements of data comprises determining the location of a “

end of block”

in the compressed serial data.

24. The method of claim 23 wherein the step of applying a transform includes using a discrete inverse cosine transform.

25. The method of claim 23 wherein the step of applying a transform includes using a 1×

1 inverse discrete cosine transform.

26. The method of claim 23 wherein the step of applying a transform includes using a 2×

2 inverse discrete cosine transform.

27. The method of claim 23 wherein the step of applying a transform includes using a 4×

4 inverse discrete cosine transform.