Signal compression and decompression
View Patent ↗A method of data compression, for example for image or audio signals, comprises encoding the data using a transform such as a wavelet transform or DCT, and transmitting only a predefined number of the most significant bits for each coefficient. It has been found experimentally that while such a method may marginally decrease the signal to noise ratio, the subjective quality of the received image or audio signal is nevertheless enhanced.
1. A method of data compression comprising:
applying a transform to the data to derive a plurality of transform coefficients each comprising a plurality of bits;
determining a most significant bit for each coefficient; and
storing or transmitting as compressed data without leading zeros, the most significant bit of each coefficient and subsequent bits down to a pre-defined number of bits that specifies, for each coefficient, an identical number of bits to be stored or transmitted.
2. A method of data compression according to claim 1 in which the transform creates coefficients in a plurality of frequency sub-bands, the pre-defined number of bits being a fixed number of bits within each of the sub-bands.
3. A method of data compression according to claim 1 in which the transform is a wavelet transform.
4. A method of data compression according to claim 1 in which the transform is a discrete cosine transform.
5. A method of data compression according to claim 1 in which the transform is a lapped orthogonal transform.
6. A method of data compression according to claim 1 in which the pre-defined number of bits is determined experimentally according to the perceived quality of data derived from a test range of compressed data.
7. A method of data compression according to claim 1 in which the data to be compressed is representative of a sequence of images.
8. A method of data compression according to claim 1 in which the determining step comprises psycho-visual experimentation.
9. A method of data compression according to claim 1 in which the determining step comprises psycho-auditory experimentation.
10. A method of data compression according to claim 1 in which the pre-defined number of bits is defined at least partially as a function of the image.
11. A method of data compression according to claim 7 in which the transform is a block transform and creates intra-frames and residual frames.
12. A method of data compression according to claim 11 in which the data to be compressed comprises the intra-frames.
13. A method of data compression according to claim 11 in which the data to be compressed comprises the residual frame.
14. A method of data compression according to claim 1 in which the pre-defined number of bits is hard-coded.
15. A method of data compression according to claim 1 in which the pre-defined number of bits is user-adjustable.
16. A method of data compression according to claim 1 in which the pre-defined number of bits is adjustable under program control.
17. A coder for carrying out the method of claim 1 .
18. A codec including a coder as claimed in claim 17 .
19. A method of data compression according to claim 1 in which the data to be compressed is representative of a still image.
20. A method of data compression according to claim 1 in which the data to be compressed is representative of audio information.
21. A computer-readable medium having stored thereon computer-executable instructions for performing steps comprising:
applying a transform to data to derive a plurality of transform coefficients each comprising a plurality of bits;
determining a most significant bit for each coefficient; and
storing or transmitting as compressed data without leading zeros, the most significant bit of each coefficient and subsequent bits down to a pre-defined number of bits that specifies, for each coefficient, an identical number of bits to be stored or transmitted.
22. The computer-readable medium of claim 21 , wherein the transform creates coefficients in a plurality of frequency sub-bands, the pre-defined number of bits being a fixed number of bits within each of the sub-bands.
23. The computer-readable medium of claim 21 , wherein the transform is a wavelet transform.
24. The computer-readable medium of claim 21 , wherein the transform is a discrete cosine transform.
25. The computer-readable medium of claim 21 , wherein the transform is a lapped orthogonal transform.
26. The computer-readable medium of claim 21 , wherein the pre-defined number of bits is determined experimentally according to the perceived quality of data derived from a test range of compressed data.
27. The computer-readable medium of claim 21 , wherein the data to be compressed is representative of a still image.
28. The computer-readable medium of claim 21 , wherein the data to be compressed is representative of a sequence of images.
29. The computer-readable medium of claim 21 , wherein the data to be compressed is representative of audio information.
30. The computer-readable medium of claim 27 , wherein the determining step comprises psycho-visual experimentation.
31. The computer-readable medium of claim 29 , wherein the determining step comprises psycho-auditory experimentation.
32. The computer-readable medium of claim 27 , wherein the pre-defined number of bits is defined at least partially as a function of the image.
33. The computer-readable medium of claim 28 , wherein the transform is a block transform and creates intra-frames and residual frames.
34. The computer-readable medium of claim 33 , wherein the data to be compressed comprises the intra-frames.
35. The computer-readable medium of claim 33 , wherein the data to be compressed comprises the residual frame.
36. The computer-readable medium of claim 21 , wherein the pre-defined number of bits is hard-coded.
37. The computer-readable medium of claim 21 , wherein the pre-defined number of bits is user-adjustable.
38. The computer-readable medium of claim 21 , wherein the pre-defined number of bits is adjustable under program control.
39. An encoder comprising:
a transform coder that applies a transform to data to derive a plurality of transform coefficients each comprising a plurality of bits; and
a coefficient coder that identifies a most significant bit of each coefficient and subsequent bits down to a pre-defined number of bits that specifies, for each coefficient, an identical number of bits to be stored or transmitted.
40. The encoder of claim 39 , wherein the transform creates coefficients in a plurality of frequency sub-bands, the pre-defined number of bits being a fixed number of bits within each of the sub-bands.
41. The encoder of claim 39 , wherein the transform is a wavelet transform.
42. The encoder of claim 39 , wherein the transform is a discrete cosine transform.
43. The encoder of claim 39 , wherein the transform is a lapped orthogonal transform.
44. The encoder of claim 39 , wherein the pre-defined number of bits is determined experimentally according to the perceived quality of data derived from a test range of compressed data.
45. The encoder of claim 39 , wherein the data is representative of a still image.
46. The encoder of claim 39 , wherein the data is representative of a sequence of images.
47. The encoder of claim 39 , wherein the data is representative of audio information.
48. The encoder of claim 45 , wherein the pre-defined number of bits is defined at least partially as a function of the image.
49. The encoder of claim 46 , wherein the transform is a block transform and creates intra-frames and residual frames.
50. The encoder of claim 49 , wherein the data comprises the intra-frames.
51. The encoder of claim 49 , wherein the data comprises the residual frame.
52. The encoder of claim 39 , wherein the pre-defined number of bits is hard-coded.
53. The encoder of claim 39 , wherein the pre-defined number of bits is user-adjustable.
54. The encoder of claim 39 , wherein the pre-defined number of bits is adjustable under program control.