Method and system for achieving coding gains in wavelet-based image codecs

• US 6,697,521 B2
• Filed: 06/15/2001
• Issued: 02/24/2004
• Est. Priority Date: 06/15/2001
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Islam, Asad, Chebil, Fehmi
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): SHERALI, ISHRAT I
• Application Number:
  US09/883,105
• Publication Number:
  US 20030002734A1
• Time in Patent Office: 984 Days
• Field of Search: 382/166, 382/233, 382/232, 382/162, 382/167, 382/240, 382/244-248, 358/539, 358/426.1, 358/426.2, 358/426.13, 358/426.14, 358/426.16, 375/240.11, 375/240.18, 375/240.21, 375/240.23, 375/240.25, 348/472
• US Class Current: 382/166
• CPC Class Codes: H04N 19/10 using adaptive coding
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/63 using sub-band based transform, e.g. wavelets

Abstract

A method and system for coding a RGB image in an encoder and a decoder. In the encoder, the RGB image components are converted into YUV components. One or more of the lower bit-planes of YUV components are eliminated before the YUV components are transformed by forward wavelet transform and coded into a codestream for transmission. In the decoder, the codestream is decoded and transformed by inverse wavelet transform into a set of reconstructed YUV components. The bit-planes of these reconstructed YUV components are up-shifted so that the up-shifted YUV components are structurally equivalent to the original YUV components before they are adjusted in the encoder. However, the lower bit-planes that come into being due to the up-shifting are all set to zero. The up-shifted YUV components are then converted into the RGB component of the reconstructed image.

Claims

1. A method of encoding an image separated into a plurality of first color components of a first color space, wherein the first color components are converted into a plurality of second color components of a second color space different from the first color space, each of the second color components having a number of more-significant bit-planes and a first number of less-significant bit-planes, said encoding method comprising the steps of:

adjusting the second color components by changing the first number of less-significant bit-planes of at least one of the second color components to a second number smaller than the first number;

transforming the adjusted second color components based on a forward wavelet transformation for providing transformed image data; and

coding the transformed image data for forming a bitstream indicative of the transformed image data.

2. The encoding method of claim 1, wherein the first number is 1 and the second number is 0.

3. The encoding method of claim 1, wherein the first and second numbers are predetermined.

4. The encoding method of claim 1, wherein the second color components include one luminance component and two chrominance components and the first number is 2, and wherein the second number of bit-planes in the luminance component is 0 and the second number of bit planes in the chrominance components is 1.

5. The encoding method of claim 4, wherein the number of the more-significant bit-planes is 6.

6. The encoding method of claim 4, wherein the number of the more-significant bit-planes is 0.

7. The encoding method of claim 1, wherein the adjusted second color components include one luminance component having 6 or 7 bit-planes and two chrominance components each having 7 bit-planes.

8. The encoding method of claim 1, wherein the adjusting step is achieved by bit-shifting.

9. The encoding method of claim 1, wherein the adjusting step is achieved through a look-up table.

10. The encoding method of claim 1, wherein the first color space is an RGB space and the second color space is a YUV color space.

11. The encoding method of claim 1, wherein the second color space is based on a representation comprising a luminance component and at least one color difference component.

12. An apparatus for encoding an image separated into a plurality of first color components of a first color space, wherein the first color components are converted into a plurality of second color components of a second color space different from the first color space, each of the second color components having a number of more-significant bit-planes and a first number of less-significant bit-planes, said apparatus comprising:

means, responsive to the second color components, for adjusting from at least one of the second color components the first number of bit-planes to a second number smaller than the first number for providing adjusted second color components;

means for transforming the adjusted color components into transformed image data based on a forward wavelet transformation for providing a signal indicative of the transformed image data, and

means, responsive to the signal, for coding the transformed image data and forming a bitstream indicative of the coded transformed image data.

13. The apparatus of claim 12, wherein the adjusting means comprises a bit-shifter for effecting the bit-plane reduction.

14. The apparatus of claim 12, wherein the adjusting means comprises a bit-shifting software program for effecting the bit-plane reduction.

15. The apparatus of claim 12, wherein the adjusting means comprises a look-up table for effecting the bit-plane reduction.

16. The apparatus of claim 12, wherein the second number of each of the second color components is predetermined, said apparatus further comprising means for storing the pre-determined second numbers and the adjusting means providing the second color components based on the stored second number.

17. The apparatus of claim 12, further comprising means for obtaining the second number of each of the second color components so as to allow the adjusting means to adjust the second color components to the adjusted second color components.

18. The apparatus of claim 12, wherein the first color space is an RGB color space and the second color space is a YUV color space.

19. A software program product embodied in a computer readable medium for use in an encoder having transform means and coding means for processing image data indicative of an image into a bitstream, wherein the image is separated into a plurality of first color components of a first color space, and the first color components are converted into a plurality of second color components of a second color space different from the first color space, each of the second color components having a plurality of more-significant bit-planes and a first number of less-significant bit-planes, said software program comprising the steps of:

adjusting, from at least one of the second color components, the first number of bit-planes to a second number smaller than the first number for providing adjusted second color components;

providing the adjusted second color components to the transform means so as to allow the transform means to transform the adjusted second color components based on a forward wavelet transformation into transformed image data, and the coding means to form the bitstream indicative of the transformed image data.

20. The software program of claim 19, wherein the adjusting step is based on bit-shifting.

21. The software program of claim 19, wherein the adjusting step is based on a look-up table.

22. An apparatus for processing a bitstream having coded data indicative of an image into a reconstructed image, wherein

the image is separated into a plurality of first color components of a first color space;

the first color components are converted into a plurality of second color components of a second color space different from the first color space, each of the second color components having a first number of more-significant bit-planes and a second number of less-significant bit-planes;

the second color components are adjusted into adjusted second color components by changing, from at least one of the second color components, the second number of bit-planes to a corresponding third number smaller than the second number for providing adjusted second color components in the second color space;

the adjusted color components are transformed into transformed image data based on a forward wavelet transformation; and

the transformed data is coded into the bitstream having the coded data, said apparatus comprising;

means, responsive to the bitstream, for decoding the coded data for providing reconstructed transformed data;

means for processing the reconstructed transformed data based on an inverse wavelet transformation for providing first reconstructed color components in the second color space;

means for changing the first reconstructed color components into second reconstructed color components in the second color space, such that each of the second reconstructed color components has a number of more-significant bit-planes equal to the first number, and a number of less-significant bit-planes equal to the second number.

23. The apparatus of claim 22, further comprising means for converting the second reconstructed color components in the second color space into third reconstructed color components in the first color space for forming the reconstructed image, wherein each of the third reconstructed color components has a number of more-significant bit-planes equal to the first number, and a number of less-significant bit-planes equal to the second number.

24. The apparatus of claim 22, wherein the first color space is an RGB color space and the second color space is a YUV space.

25. The apparatus of claim 22, wherein the corresponding third number of said at least one of the second color components is predetermined, said apparatus further comprising means for obtaining said corresponding third number so as to allow the changing means to change the first reconstructed color components into the second reconstructed color components based on the obtained third number.

26. The apparatus of claim 22, wherein the corresponding third number of said at least one of the second color components is included in the bitstream so as to allow the changing means to change the first reconstructed color components into the second reconstructed color components based on the included third number.

27. The apparatus of claim 22, wherein each of the first reconstructed color components is corresponding to one of the second color components, and each of the first reconstructed color components has a number of more-significant bit-planes equal to the first number, and a number of less-significant bit-planes equal to the third number of less-significant bit-planes of the corresponding one of the second color components.

28. A software program product embodied in a computer readable medium for use in an apparatus for processing a bitstream having coded data indicative of an image into a reconstructed image, wherein

the image is separated into a plurality of first color components of a first color space;

the first color components are converted into a plurality of second color components of a second color space different from the first color space, each of the second color components having a first number of more-significant bit-planes and a second number of less-significant bit-planes;

the second color components are adjusted into adjusted second color components by changing, from at least one of the second color components, the second number of bit-planes to a corresponding third number smaller than the second number for providing adjusted second color components in the second color space;

the adjusted color components are transformed into transformed image data based on a forward wavelet transformation; and

the transformed data is coded into the bitstream having the coded data, said apparatus comprising;

means, responsive to the bitstream, for decoding the coded data for providing reconstructed transformed data;

means for processing the reconstructed transformed data based on an inverse wavelet transformation for providing first reconstructed color components in the second color space, each of the first reconstructed color components corresponding to one of the second color components, wherein each of the first reconstructed color components has a number of more-significant bit-planes equal to the first number, and a fourth number of less-significant number of bit-planes equal to the corresponding third number;

said software program comprising the steps of;

changing the first reconstructed color components into second reconstructed color components in the second color space, effectively adding a number of bit-planes to at least one of the first reconstructed color components corresponding to said at least one of the second color components such that each of the second reconstructed color components has a number of more-significant bit-planes equal to the first number, and a number of less-significant bit-planes equal to the second number; and

setting pixel values of the added bit-planes to zero.

29. The software program of claim 28, wherein the changing step is based on bit-shifting.

30. The software program of claim 28, wherein the changing step is achieved through a look-up table.

31. A system for coding an image into a bitstream and decoding the bitstream into a reconstructed image, wherein the image is separated into a plurality of first color components of a first color space, and the first color components are converted into a plurality of second color components of a second space different from the first color space, wherein each of the second color components has a first number of more-significant bit-planes and a second number of less-significant bit planes, said system comprising:

means, responsive to the second color components, for adjusting at least one of the second color components the second number of bit-planes to a corresponding third number smaller than the second number for providing adjusted second color components in the second color space;

means for transforming the adjusted second color components into transformed image data based on a forward wavelet transformation for providing a signal indicative of the transformed image data;

means, responsive to the signal, for coding the transformed image data and forming a bitstream having coded information indicated of the coded transformed image data;

means, responsive to the bitstream, for decoding the coded information for providing reconstructed transformed data;

means for processing the reconstructed transformed data based on an inverse wavelet transformation for providing first reconstructed color components in the second color space; and

means for changing the first reconstructed color components into second reconstructed color components in the second color space indicative of the reconstructed image, such that each of the second reconstructed color components has a number of more-significant bit-planes equal to the first number, and a number of less-significant bit-planes equal to the second number.

32. The system of claim 31, further comprising means for converting the second reconstructed color components in the second space into third reconstructed color components in the first color space for forming the reconstructed image.

33. The system of claim 31, wherein each of the first reconstructed color components is corresponding to one of the second color components, and wherein each of the first reconstructed color components has a number of less-significant bit-planes equal to the third number of less-significant bit-planes of the corresponding one of the second color components.

34. The system of claim 31, wherein the first color space is an RGB color space, and

the second color space is a YUV color space.