Signaling for illumination compensation

1. A method comprising:

receiving a first block of pixels in a first video picture to be coded as a current block, wherein the current block is associated with a motion vector that references a second block of pixels in a second video picture as a reference block;

performing inter-prediction for the current block by using the motion vector to generate a set of motion-compensated pixels for the current block; and

modifying the set of motion-compensated pixels of the current block by applying a linear model that is computed based on neighboring samples of the reference block and of the current block, wherein the neighboring samples are identified based on a position of the current block within a larger block.

2. The method of claim 1 , wherein the linear model is based on a set of illumination compensation parameters comprising a scaling factor and an offset.

3. The method of claim 1 , wherein the larger block comprises a plurality of sub-blocks, wherein a first sub-block is the current block, wherein neighboring pixels of the first sub-block are used as the neighboring samples of the current block to compute the linear model that is used to modify the current block and other sub-blocks of the larger block.

4. The method of claim 1 , wherein the current block is a coding unit (CU) and the larger block is a coding tree unit (CTU) that includes a plurality of CUs, wherein the identified neighboring samples of the current block are derived based on neighboring pixels of the CTU.

5. The method of claim 1 , wherein the current block is a prediction unit (PU) and the larger bock is a coding unit (CU) that includes a plurality of PUs and has a size that is greater than a threshold, wherein the identified neighboring samples of the current block are derived based on neighboring pixels of the CU.

6. The method of claim 1 , wherein the neighboring samples of the current block are neighboring pixels of the larger block that are vertically or horizontally aligned with the current block.

7. The method of claim 1 , wherein the identified neighboring samples of the current block comprises neighboring pixels above the larger block and no other pixels when the current block is at a top edge of the larger block but not at a left edge of the larger block.

8. The method of claim 1 , wherein the identified neighboring samples of the current block comprises neighboring pixels left of the larger block and no other pixels when the current block is at a left edge of the larger block but not at a top edge of the larger block.

9. The method of claim 1 , wherein the identified neighboring samples are computed by using reconstructed pixels based on prediction pixels and residual pixels of a neighboring block when the residual pixels of the neighboring block are available; and by using the prediction pixels of the neighboring block when the residual pixels of the neighboring block are not available.

10. The method of claim 1 , wherein the linear model is inherited from a neighboring block of the current block.

11. The method of claim 1 , wherein the larger block comprises a plurality of sub-blocks that includes the current block, wherein neighboring pixels of the larger block are sub-sampled and used as the neighboring samples to compute the linear model that is used to modify the current block and other sub-blocks of the larger block.

12. The method of claim 1 , wherein performing inter-prediction for the current block comprises generating a set of prediction pixels for the current block, and wherein modifying the set of motion-compensated pixels of the current block comprises applying the linear model to refine the set of prediction pixels of the current block.

13. A method comprising:

receiving a first block of pixels in a first video picture to be coded as a current block, wherein the current block is associated with a motion vector that references a second block of pixels in a second video picture as a reference block;

performing inter-prediction for the current block by using the motion vector to generate a set of motion-compensated pixels for the current block;

determining whether to enable illumination compensation mode based on a prediction setting of the current block; and

modifying the current block by applying a linear model when the illumination compensation mode is enabled.

14. The method of claim 13 , wherein the illumination compensation mode is disabled when a size of the current block is larger than a threshold.

15. The method of claim 13 , wherein determining whether to enable the illumination compensation mode is further based on a position of the current block within a larger block.

16. The method of claim 15 , wherein illumination compensation mode is disabled when the current block is not a top-most block or a left-most block of the larger block.

17. The method of claim 13 , further comprising disabling the illumination compensation mode when at least one of General Bi-prediction (GBi), Bi-directional optical flow (BIO), Sub-PU Temporal Motion Vector Prediction (SPTMVP or ATMVP), Affine mode, Bilateral Template MV Refinement (DMVR), Multi-hypothesis Intra-Merge mode, Multi-hypothesis Merge mode, and Multi-hypothesis Merge+AMVP mode is turned on for the current block.

18. An electronic apparatus comprising:

an encoder circuit capable of:

receiving a first block of pixels in a first video picture to be encoded a current block, wherein the current block is associated with a motion vector that references a second block of pixels in a second video picture as a reference block;

performing inter-prediction for the current block by using the motion vector to generate a set of motion-compensated pixels for the current block;

modifying the set of motion-compensated pixels of the current block by applying a linear model that is computed based on neighboring samples of the reference block and of the current block, wherein the neighboring samples are identified based on a position of the current block within a larger block; and

encoding the modified set of motion-compensated pixels of the current block into a bitstream.

19. The electronic apparatus of claim 18 , wherein the modifying is based on enablement of an illumination compensation mode.

20. The method of claim 1 , wherein the modifying is based on enablement of an illumination compensation mode.