Local illumination compensation for inter prediction

1 . A method for video decoding, comprising:

receiving and decoding a bit-stream to obtain a prediction residual and prediction mode information indicating a mode of Local Illumination Compensation (LIC) to be enabled;

forming a residual block from the prediction residual and forming a prediction block from the prediction mode information; and

reconstructing a reconstructed block from the residual block and prediction block;

wherein LIC parameters for the mode of LIC are calculated with a limited number of reference sample pairs, and wherein a reference sample pair refers to a luma reference sample and a chroma reference sample,

wherein one or more Multi-model LIC (MMLIC) modes are added to the mode of LIC,

wherein in each MMLIC mode, the reference sample pairs are classified into a number of groups and the LIC parameters are calculated for each group, and

wherein the reference sample pairs are classified into the number of groups by a threshold which is calculated by an average value of neighbouring reconstructed luma samples or the maximum and minimum value of the neighbouring reconstructed luma samples.

2 . The method of claim 1 , wherein the maximum number of reference sample pairs for calculating the LIC parameters is limited to a pre-determined value based on a size and shape of a chroma block.

3 . The method of claim 1 , wherein the limited number of reference samples pairs are selected by taking one out of every two neighboring reference sample pairs.

4 . The method of claim 1 , wherein the LIC parameters are calculated using up to 8 reference sample pairs.

5 . The method of claim 1 , wherein the mode of LIC is replaced with a MMLIC mode.

6 . The method of claim 1 , wherein the reference sample pairs are classified into the number of groups with block based pixel classification where a classification decision is applied to all pixels in a block.

7 . The method of claim 1 , wherein the reference sample pairs are classified into three groups.

8 . The method of claim 1 , wherein the threshold is calculated with reconstructed luma samples in a current block.

9 . The method of claim 1 , wherein LIC is performed with the calculated LIC parameters for each group of the number of groups to generate a number of predicted samples; and

wherein the number of predicted samples are weighted to generate a final prediction.

10 . The method of claim 1 , wherein the mode of Local Illumination Compensation (LIC) is determined adaptively by a condition check based on block size.

11 . An apparatus for video decoding, comprising:

a memory to store an instruction; and

a processor to execute the instruction such that the processor is configured to:

receive and decode a bit-stream to obtain a prediction residual and prediction mode information indicating a mode of Local Illumination Compensation (LIC) to be enabled;

form a residual block from the prediction residual and form a prediction block from the prediction mode information; and

reconstruct a reconstructed block from the residual block and prediction block;

wherein LIC parameters for the mode of LIC are calculated with a limited number of reference sample pairs, and wherein a reference sample pair refers to a luma reference sample and a chroma reference sample,

wherein one or more Multi-model LIC (MMLIC) modes are added to the mode of LIC,

wherein in each MMLIC mode, the reference sample pairs are classified into a number of groups and the LIC parameters are calculated for each group, and

wherein the reference sample pairs are classified into the number of groups by a threshold which is calculated by an average value of neighbouring reconstructed luma samples or the maximum and minimum value of the neighbouring reconstructed luma samples.

12 . The apparatus of claim 11 , wherein the maximum number of reference sample pairs for calculating the LIC parameters is limited to a pre-determined value based on a size and shape of a chroma block.

13 . The apparatus of claim 11 , wherein the limited number of reference samples pairs are selected by taking one out of every two neighboring reference sample pairs.

14 . The apparatus of claim 11 , wherein the LIC parameters are calculated using up to 8 reference sample pairs.

15 . The apparatus of claim 11 , wherein the mode of LIC is replaced with a MMLIC mode.

16 . The apparatus of claim 11 , wherein the reference sample pairs are classified into the number of groups with block based pixel classification where a classification decision is applied to all pixels in a block.

17 . A non-transitory machine-readable storage medium, having instructions stored on the medium, the instructions configured to, when executed, cause a machine to:

receive and decode a bit-stream to obtain a prediction residual and prediction mode information indicating a mode of Local Illumination Compensation (LIC) to be enabled;

form a residual block from the prediction residual and form a prediction block from the prediction mode information; and

reconstruct a reconstructed block from the residual block and prediction block;

wherein LIC parameters for the mode of LIC are calculated with a limited number of reference sample pairs, and wherein a reference sample pair refers to a luma reference sample and a chroma reference sample,

wherein one or more Multi-model LIC (MMLIC) modes are added to the mode of LIC,

wherein in each MMLIC mode, the reference sample pairs are classified into a number of groups and the LIC parameters are calculated for each group, and

wherein the reference sample pairs are classified into the number of groups by a threshold which is calculated by an average value of neighbouring reconstructed luma samples or the maximum and minimum value of the neighbouring reconstructed luma samples.