Method and apparatus for encoding and decoding image using modification of residual block

• US 8,194,989 B2
• Filed: 02/15/2008
• Issued: 06/05/2012
• Est. Priority Date: 04/06/2007
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Jae-chool, Han, Woo-jin
• Primary Examiner(s): Wu, Jingge
• Assistant Examiner(s): MOTSINGER, SEAN T
• Application Number:
  US12/032,056
• Publication Number:
  US 20080247658A1
• Time in Patent Office: 1,572 Days
• Field of Search: 382232-253, 348240-241
• US Class Current: 382/239
• 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 19/182 the unit being a pixel
• CPC Class Codes: H04N 19/20 using video object coding
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/649 the transform being applied to non rectangular image segments

Abstract

Provided are a method and apparatus for encoding and decoding an image. In the encoding method, a residual block of a current block is transformed using a predicted block of the current block so as to increase the spatial correlation among residual values, and DCT is performed on the transformed residual block, thus improving the efficiency of transforming a block having a region that is difficult to precisely predict.

Claims

1. A method of encoding an image, comprising:

generating a predicted block of a current block, and subtracting the predicted block from the current block to generate a residual block of the current block;

generating information for increasing a spatial correlation among residual values included in the residual block based on the predicted block, and transforming the residual block based on the information; and

performing discrete cosine transformation (DCT) on a part of the transformed residual block based on the information,

wherein the generating of the information comprises generating a gradient map of the predicted block.

2. The method of claim 1, wherein the performing of the DCT comprises performing shape-adaptive DCT on the transformed residual block.

3. The method of claim 1, wherein the generating of the information and transforming of the residual block comprises:

selecting residual values on which the DCT is to be performed, from among the residual values of the residual block, based on the gradient map; and

shifting the selected residual values to the top and the left side of the residual block.

4. The method of claim 3, wherein the performing of the DCT comprises performing shape-adaptive DCT on the shifted residual values.

5. The method of claim 4, further comprising performing entropy encoding only on coefficients obtained by the performing shape-adaptive DCT, according to the gradient map.

6. The method of claim 5, wherein the performing of entropy encoding comprises generating a significant map only of the coefficients obtained by the performing shape-adaptive DCT.

7. An apparatus for encoding an image, the apparatus comprising:

a prediction unit which generates a predicted block of a current block;

a subtraction unit which generates a residual block of the current block by subtracting the predicted block from the current block;

a pre-processor which generates information for increasing the spatial correlation among values of residuals included in the residual block based on the predicted block, and transforming the residual block based on the information; and

a transformation unit which performs discrete cosine transformation (DCT) on a part of the transformed residual block based on the information,

wherein the pre-processor comprises a gradient map generation unit which generates a gradient map of the predicted block, and

wherein at least one of the prediction unit, subtraction unit, pre-processor and the transformation unit is implemented as a hardware component.

8. The apparatus of claim 7, wherein the transformation unit performs shape-adaptive DCT on the transformed residual block.

9. The apparatus of claim 7, wherein the pre-processor comprises:

a selection unit which selects residual values on which the DCT is to be performed, from among the residual values of the residual block, based on the gradient map; and

a shift unit which shifts the selected residual values to the top and the left side of the residual block.

10. The apparatus of claim 9, wherein the transformation unit performs shape-adaptive DCT on the shifted residual values.

11. The apparatus of claim 9, further comprising an entropy encoding unit which performs entropy encoding on only coefficients obtained by performing shape-adaptive DCT, according to the gradient map.

12. The apparatus of claim 11, wherein the entropy encoding unit generates a significant map only of the coefficients obtained by the performing shape-adaptive DCT.

13. A method of decoding an image, the method comprising:

generating a predicted block of a current block, and information for increasing the spatial correlation among residual values included in a residual block of the current block based on the predicted block;

performing inverse discrete cosine transformation (DCT) on a part of DCT coefficients of the residual block, based on the information;

rearranging the residual values of the residual block which are obtained by the performing inverse DCT, based on the information; and

combining the rearranged residual block and the predicted block to restore the current block,

wherein the generating of the predicted block and the information comprises generating a gradient map of the predicted block.

14. The method of claim 13, wherein the performing of inverse DCT comprises performing shape-adaptive inverse DCT on a part of the DCT coefficients of the residual block, based on the gradient map.

15. The method of claim 14, wherein the rearranging of the residual values comprises shifting residual values included in the residual block on which the shape-adaptive inverse DCT is performed based on the gradient map.

19. A non-transitory computer readable medium having recorded thereon a program for executing the method of claim 13.

16. An apparatus for decoding an image, the apparatus comprising:

a prediction unit which generates a predicted block of a current block;

a pre-processor which generates information for increasing a spatial correlation among values of residuals included in a residual block of the current block, based on the predicted block;

an inverse transformation unit which performs inverse discrete cosine transformation (DCT) on a part of DCT coefficients of the residual block, based on the information; and

an addition unit which rearranges the residual values of the residual block which are obtained by performing inverse DCT based on the information, and combines the rearranged residual block and the predicted block to restore the current block,

wherein the pre-processor generates a gradient map of the predicted block.

17. The apparatus of claim 16, wherein the inverse transformation unit performs shape-adaptive DCT on the DCT coefficients of the residual block based on the gradient map.

18. The apparatus of claim 17, wherein the addition unit shifts the residual values of the residual block on which the shape-adaptive inverse DCT is performed based on the gradient map, and combines the shifted residual values and the predicted block to restore the current block.