Method and apparatus for illumination compensation and method and apparatus for encoding and decoding image based on illumination compensation

1. A method of compensating for illumination of a reference block, comprising:

receiving inputs of restored values of pixels neighboring a current block and restored values of pixels neighboring the reference block;

predicting mean values of pixels of the current block and the reference block, based on the input restored values of the pixels neighboring the current block and the input restored values of the pixels neighboring the reference block;

based on the predicted mean value of the pixels of the current block, the predicted mean value of the pixels of the reference block, and the values of the pixels of the current block and the reference block, determining an illumination compensation parameter for illumination compensation of the reference block; and

performing illumination compensation of the reference block, by using the determined illumination compensation parameter.

2. The method of claim 1 , wherein the predicting of the mean values of the pixels of the current block and the reference block comprises predicting the mean value of the values of the pixels neighboring the current block to be the mean value of the pixels of the current block, and predicting the mean value of the values of the pixels neighboring the reference block to be the mean value of the pixels of the reference block.

3. The method of claim 1 , wherein the determining of an illumination compensation parameter for illumination compensation of the reference block further comprises determining an illumination compensation parameter which minimizes a difference between the pixels of an illumination-compensated reference block and the original pixels of the current block, the illumination-compensated reference block being generated by multiplying the difference between the restored pixels of the reference block and the mean value of the pixels neighboring the reference block, by a predetermined illumination compensation parameter, and then, adding the mean value of the pixels neighboring the current block.

4. The method of claim 1 , wherein the determining of an illumination compensation parameter for illumination compensation of the reference block comprises:

assuming that an illumination compensation parameter is a x,y , a size of each of the current block and the reference block is M×N, the pixel value at a position (i,j) in the current block is f(i,j), the predicted value of the pixel value at the position (i,j) in the current block is f E (i,j), the restored value of the pixel value at a position (i,j) in the reference block is r′ x,y (i,j), generating the illumination-compensated reference block by using the following equation:

f E ( i,j )= a x,y ( r′ x,y ( i,j )−DC r )+DC jl

where M, N, i and j are positive integers, 0≦i≦M, 0≦j≦N, wherein DC r is a mean value of the pixels neighboring a restored reference block, and wherein DC f is a mean value of the pixels neighboring a restored current block; and

calculating a sum of the differences between each pixel value f(i,j) and the predicted value f E (i,j) of the current block, and determining an illumination compensation parameter a x,y which minimizes the sum of the differences.

5. The method of claim 1 , wherein the determining of an illumination compensation parameter for illumination compensation of the reference block comprises determining an illumination compensation parameter from a predetermined number of predefined illumination compensation parameters so that the difference between the pixel values of the illumination-compensated reference block and the current block is minimized.

6. The method of claim 1 , wherein the determining of an illumination compensation parameter for illumination compensation of the reference block is performed according to one of two modes comprising a variable mode in which a different illumination compensation parameter is determined for a block of a predetermined size, and a fixed mode in which an identical illumination compensation parameter is determined for sub blocks in the block of the predetermined size.

7. An apparatus for compensating for illumination of a reference block, comprising:

a processor;

a memory coupled to the processor, wherein the memory stores program instructions executable by the processor to implement:

a mean value prediction unit which predicts mean values of pixels of a current block and the reference block, based on restored values of pixels neighboring the current block and restored values of pixels neighboring the reference block;

an illumination compensation parameter calculation unit, based on the predicted mean value of the pixels of the current block, the predicted mean value of the pixels of the reference block, and the values of the pixels of the current block and the reference block, determining an illumination compensation parameter for illumination compensation of the reference block; and

an illumination compensation unit which performs illumination compensation of the reference block, by using the determined illumination compensation parameter.

8. The apparatus of claim 7 , wherein the mean value prediction unit predicts the mean value of the values of the pixels neighboring the current block to be the mean value of the pixels of the current block, and the mean value of the values of the pixels neighboring the reference block to be the mean value of the pixels of the reference block.

9. The apparatus of claim 7 , wherein the illumination compensation parameter calculation unit determines an illumination compensation parameter which minimizes a difference between the pixels of an illumination-compensated reference block and the original pixels of the current block, the illumination-compensated reference block being generated by multiplying a difference between the restored pixels of the reference block and the mean value of the pixels neighboring the reference block, by a predetermined illumination compensation parameter, and then, adding the mean value of the pixels neighboring the current block.

10. The apparatus of claim 7 , wherein, assuming that an illumination compensation parameter is a x,y , a size of each of the current block and the reference block is M×N, the pixel value at a position (i,j in the current block is f(i,j), the predicted value of the pixel value at the position (i,j) in the current block is f E (i,j), the restored value of the pixel value at a position (i,j) in the reference block is r′ x,y (i,j), the illumination compensation unit generates the illumination-compensated reference block by using the following equation:

f E ( i,j )= a x,y ( r′ x,y ( i,j )−DC r )+DC j

where M, N, i and j are positive integers, 0≦i≦M, 0≦j≦N, wherein DC r is a mean value of the pixels neighboring a restored reference block, and wherein DC f is a mean value of the pixels neighboring a restored current block; and

the illumination compensation parameter calculation unit calculates a sum of the differences between each pixel value f(i,j) and the predicted value f E (i,j) of the current block, and determines an illumination compensation parameter a x,y which minimizes the sum of the differences.

11. The apparatus of claim 7 , wherein the illumination compensation parameter calculation unit determines an illumination compensation parameter from a predetermined number of predefined illumination compensation parameters so that a difference between the pixel values of the illumination-compensated reference block and the current block is minimized.

12. The apparatus of claim 7 , wherein the illumination compensation parameter calculation unit determines the illumination compensation parameter for illumination compensation of the reference block according to one of two modes comprising a variable mode in which a different illumination compensation parameter is determined for a block of a predetermined size, and a fixed mode in which an identical illumination compensation parameter is determined for sub blocks in the block of the predetermined size.