Methods and apparatus for prediction refinement with optical flow

A bit-depth representation method of prediction refinement with optical flow (PROF) for decoding a video signal, comprising:

• obtaining, at the decoder, a first reference picture I associated with a video block within the video signal;
• obtaining, at the decoder, prediction samples I(i, j) of the video block from a reference block in the first reference picture I, wherein i and j represent a coordinate of one sample within the video block;
• controlling, at the decoder, internal bit-depths of a PROF derivation process for various representation precisions of internal PROF parameters by applying right-shifting to the internal PROF parameters based on a first bit-shift value na, wherein the internal PROF parameters comprise horizontal gradient values, vertical gradient values, horizontal motion difference values, and vertical motion difference values derived for the prediction samples I(i, j);
• obtaining, at the decoder, prediction refinement values for samples in the video block based on the PROF derivation process being applied to the video block based on the prediction samples I(i, j);
• and
• obtaining, at the decoder, final prediction samples of the video block based on the combination of the prediction samples I(i, j) and the prediction refinement values.

A computing device comprising:

• one or more processors;
• a non-transitory computer-readable storage medium storing instructions executable by the one or more processors, wherein the one or more processors are configured to:
• obtain a first reference picture I associated with a video block that is coded by affine mode within the video signal;
• obtain control point motion vectors (CPMVs) of an affine coding block based on the video block;
• obtain prediction samples I(i, j) of the affine coding block from reference samples in the first reference picture I based on the CPMVs, wherein i and j represent a coordinate of one sample within the video block;
• derive prediction refinement with optical flow (PROF) prediction sample refinements of the affine coding block based on PROF;
• receive a local illumination compensation (LIC) flag that indicates whether an LIC is applied to the affine coding block;
• derive, in response to determining that the LIC is applied, LIC weight and offset based on neighboring reconstructed samples of the affine coding block and their corresponding reference samples in the first reference picture;
• and
• obtain final prediction samples of the affine coding block based on the PROF prediction sample refinements and the LIC weight and offset.