| CPC H04N 19/186 (2014.11) [H04N 19/119 (2014.11); H04N 19/136 (2014.11); H04N 19/176 (2014.11); H04N 19/52 (2014.11); H04N 19/55 (2014.11)] | 16 Claims |
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1. A method of coding video data, comprising:
determining, during a first conversion between a luma block of a video and a bitstream of the video, that motion vectors of control points of the luma block based on an affine mode;
dividing the luma block into a first group of sub-blocks, wherein each sub-block of the first group has a first size;
reconstructing a first group of sub-blocks based on the motion vectors of the control points;
reconstructing a second group of sub-blocks of a chroma block corresponding to the luma block, wherein each sub-block of the second group has a second size, and the second size is equal to the first size when a color format applied for the luma block and the chroma block is 4:2:0 or 4:2:2,
wherein the method further comprises:
determining, during a second conversion between a current video unit of the video and the bitstream of the video, that motion vectors of control points of the current video unit are based on the affine mode, wherein whether a first affine mode or a second affine mode is allowed for the current video unit is based on a same dimension constraint, wherein the current video unit comprises a luma component and at least one chroma component;
dividing the luma component into luma sub-blocks;
dividing a chroma component of the at least one chroma component into chroma sub-blocks;
determining a luma motion vector for each luma sub-block based on the motion vectors of the control points;
deriving a chroma motion vector for each chroma sub-block based on luma motion vectors of multiple corresponding luma sub-blocks and the color format of the current video unit; and
reconstructing the luma component based on the luma motion vector of each luma sub-block,
wherein deriving the chroma motion vector for each chroma sub-block comprises:
determining that the chroma component is divided into at least one first chroma group, wherein the first chroma group includes two or four chroma sub-blocks according to the color format of the current video unit;
deriving a group chroma motion vector for each one of the at least one first chroma group; and
assigning the group chroma motion vector to each sub-block of the corresponding first chroma group,
wherein the group chroma motion vector is derived based on applying a scaling factor to an intermediate motion vector MV*.
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