Alignment of prediction weights in video coding

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• determine, during a conversion between a current chroma block of a video and a bitstream of the video, that the current chroma block is coded with a geometric partitioning mode;
• determine a first motion information and a second motion information;
• determine chroma weights used for determining a final chroma prediction for the current chroma block by a blending process;
• and
• perform the conversion based on the first motion information, the second motion information and the chroma weights, wherein the conversion comprises applying the blending process to generate the final chroma prediction based on a weighted sum of prediction samples derived from the first motion information and the second motion information using the chroma weights,
• wherein the chroma weights are determined based on a chroma format of the current chroma block indicating a chroma subsampling ratio relative to a collocated luma block of the current chroma block, and
• wherein a chroma weight, WeightC[x][y], is equal to WeightY[f(x)][g(y)], wherein x is an integer between 0 and W/subWidthC−1, y is an integer between 0 and H/subHeightC−1, W and H are a width and a height of the collocated luma block, subWidthC and subHeightC denote chroma subsampling ratios in width and height directions, respectively, and WeightY[a][b] denotes a luma weight, a is an integer between 0 and W−1 and b is an integer between 0 and H−1.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• determine, during a conversion between a current chroma block of a video and a bitstream of the video, that the current chroma block is coded with a geometric partitioning mode;
• determine a first motion information and a second motion information;
• determine chroma weights used for determining a final chroma prediction for the current chroma block by a blending process;
• and
• perform the conversion based on the first motion information, the second motion information and the chroma weights, wherein the conversion comprises applying the blending process to generate the final chroma prediction based on a weighted sum of prediction samples derived from the first motion information and the second motion information using the chroma weights,
• wherein the chroma weights are determined based on a chroma format of the current chroma block indicating a chroma subsampling ratio relative to a collocated luma block of the current chroma block;
• and
• wherein a chroma weight, WeightC[x][y], is equal to WeightY[f(x)][g(y)], wherein x is an integer between 0 and W/subWidthC−1, y is an integer between 0 and H/subHeightC−1, W and H are a width and a height of the collocated luma block, subWidthC and subHeightC denote chroma subsampling ratios in width and height directions, respectively, and WeightY[a][b] denotes a luma weight, a is an integer between 0 and W−1 and b is an integer between 0 and H−1.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• determining that a current chroma block of the video is coded with a geometric partitioning mode;
• determining a first motion information and a second motion information;
• determining chroma weights used for determining a final chroma prediction for the current chroma block by a blending process;
• and
• generating the bitstream based on the first motion information, the second motion information and the chroma weights, wherein the generating comprises applying the blending process to generate the final chroma prediction based on a weighted sum of prediction samples derived from the first motion information and the second motion information using the chroma weights,
• wherein the chroma weights are determined based on a chroma format of the current chroma block indicating a chroma subsampling ratio relative to a collocated luma block of the current chroma block;
• and
• wherein a chroma weight, WeightC[x][y], is equle to WeightY[f(x)][g(y)], wherein x is an integer between 0 and W/subWidthC−1, y is an integer between 0 and H/subHeightC−1, W and H are a width and a height of the collocated luma block, subWidthC and subHeightC denote chroma subsampling ratios in width and height directions, respectively, and WeightY[a][b] denotes a luma weight, a is an integer between 0 and W−1 and b is an integer between 0 and H−1.