System and method for improved compression of DCT compressed images
View Patent ↗A system providing methods for improved compression of images that have been compressed using Discrete Cosine Transform (DCT) based compression is described. A digital image that has been compressed using DCT based compression, such as an image compressed using the Joint Photographic Experts Group (JPEG) compression scheme, is received and partially decompressed to generate DCT coefficients of the image. The decoded coefficients of the image are then rearranged to aggregate like frequencies together. After rearrangement, the image is recompressed using a wavelet-based compression scheme.
1. A method for transformation and improved compression of a digital image having been compressed using Discrete Cosine Transform (DCT) based compression, the method comprising:
receiving a digital image, said digital image having been compressed using Discrete Cosine Transform (DCT) based compression to generate a plurality of DCT coefficients of the image;
aggregating a first DCT coefficient from a first pixel block of the partially decompressed image with a second DCT coefficient from a second pixel block adjoining the first pixel block of the partially decompressed image based on similarity of frequencies of the first DCT coefficient and the second DCT coefficient;
partially decompressing said digital image; and
recompressing said digital image using wavelet-based compression, wherein the recompressing comprises quantizing the image and entropy coding the image.
2. The method of claim 1 , wherein said Discrete Cosine Transform (DCT) based compression includes Joint Photographic Experts Group (JPEG) compression.
3. The method of claim 1 , wherein said step of partially decompressing said digital image includes entropy decoding said digital image.
4. The method of claim 3 , wherein said step of entropy decoding includes a variable length decoding.
5. The method of claim 3 , wherein said step of entropy decoding includes a run length decoding.
6. The method of claim 1 wherein said step of partially decompressing said image includes partially decompressing said image in segments.
7. The method of claim 1 , further comprising:
rearranging said partially decompressed digital image to aggregate like frequencies together before recompressing said digital image.
8. The method of claim 7 , wherein said step of aggregating like frequencies includes aggregating Discrete Cosine Transform (DCT) coefficients of said digital image into at least eight sub-bands.
9. The method of claim 1 , wherein said step of recompressing said digital image includes transforming said digital image using a forward wavelet-based transform.
10. The method of claim 1 , wherein said step of recompressing said digital image includes using a one-dimensional wavelet-based transform.
11. The method of claim 1 , wherein said step of recompressing said digital image includes using a two-dimensional wavelet-based transform.
12. The method of claim 1 , wherein said step of recompressing said digital image includes recompressing said image in segments.
13. The method of claim 12 , wherein each said segment corresponds to a row of eight lines of pixels of said digital image.
14. The method of claim 12 , wherein said step of recompressing said image in segments includes the substeps of:
rearranging each said segment to aggregate like frequencies together; and
compressing each said segment using a wavelet-based compression.
15. The method of claim 1 , wherein said step of receiving a digital image includes retrieving said digital image from memory of a digital imaging device.
16. The method of claim 1 , wherein said steps of partially decompressing and recompressing said digital image are performed on a digital imaging device.
17. The method of claim 1 , further comprising:
transmitting said recompressed digital image from a digital imaging device to a second device.
18. The method of claim 17 wherein said set of transmitting said recompressed digital image includes transmitting said recompressed digital image in segments.
19. The method of claim 17 , further comprising:
decompressing said recompressed digital image on said second device.
20. The method of claim 17 , further comprising:
decompressing said recompressed digital image on said second device and recompressing said digital image using Joint Photographic Experts Group (JPEG) compression.
21. A computer-readable medium having computer-executable instructions for performing the method of claim 1 .
22. A downloadable set of computer-executable instructions for performing the method of claim 1 .
23. A method for transformation and improved compression of an image that has been compressed using Joint Photographic Experts Group (JPEG) compression, the method comprising:
upon receiving a JPEG compressed image, partially decompressing the image to generate Discrete Cosine Transform (DCT) coefficients of the image;
rearranging said DCT coefficients of the image to aggregate a first DCT coefficient from a first pixel block of the partially decompressed image with a second DCT coefficient from a second pixel block adjoining the first pixel block of the partially decompressed image based on similarity of frequencies of the first DCT coefficient and the second DCT coefficient; and
recompressing said digital image using wavelet-based compression.
24. The method of claim 23 , wherein said receiving step includes retrieving said digital image from memory of a digital camera.
25. The method of claim 23 , wherein said transformation and improved compression of an image is performed on a digital camera.
26. The method of claim 23 , wherein said JPEG compressed image includes an image compressed using JPEG compression and stored in JPEG File Interchange Format (JFIF).
27. The method of claim 23 , wherein said JPEG compressed image includes an image compressed using JPEG compression and stored in any file format.
28. The method of claim 23 , wherein JPEG compressed image includes an image compressed using a Discrete Cosine Transform (DCT) based compression method.
29. The method of claim 23 , wherein said partially decompressing step includes entropy decoding.
30. The method of claim 29 , wherein entropy decoding includes a run length decoding.
31. The method of claim 29 , wherein entropy decoding includes a variable length decoding.
32. The method of claim 23 , wherein said recompressing step includes recompressing the image in segments.
33. The method of claim 23 , wherein said rearranging step includes rearranging the image in segments.
34. The method of claim 23 , further comprising:
transmitting the recompressed image from a digital camera to a second device.
35. The method of claim 34 , wherein said transmitting step includes transmitting the image in segments.
36. The method of claim 34 , further comprising:
sub-sampling the image before transmission to the second device to reduce the size of the image file.
37. The method of claim 23 , wherein said recompressing step includes using a one-dimensional wavelet-based transform.
38. The method of claim 23 , wherein said recompressing step includes using a two-dimensional wavelet-based transform.
39. The method of claim 23 , wherein said recompressing includes coding the image using a wavelet-based transform.