Inter-prediction mode based image processing method, and apparatus therefor
In the present invention, an inter-prediction mode based image processing method and an apparatus therefor are disclosed. Specifically, the inter-prediction based image processing method may comprise the steps of: deriving movement information of a control point for specifying a reference block of a current block; dividing the current block into sub-blocks; deriving movement information of the sub-blocks using the movement information of the control point; and generating a prediction block for each sub-block using the movement information of the sub-blocks.
1. A method of decoding an image based on inter prediction, comprising steps of:
deriving, by a processor, at least two motion vectors of at least two control points of a current block;
splitting, by the processor, the current block into sub-blocks;
deriving, by the processor, a motion vector of each of the sub-blocks based on the at least two motion vectors of the at least two control points of the current block;
generating, by the processor, a prediction block for each of the sub-blocks based on the motion vector of each of the sub-blocks; and
updating, by the processor, the prediction block for each of the sub-blocks pixel-by-pixel based on an optical flow,
wherein the at least two motion vectors of the at least two control points of the current block are derived based on a motion vector of a control point of a neighboring block,
wherein a motion vectors of one among the at least two control points of the current block are derived based on modifying of the motion vector of a control point of the neighboring block based on a difference between a coordinate of the control point of the neighboring block and a coordinate of one of the at leat two control points of the current block, and a differnece between two motion vectors of two control points of the neighboring block with respect to at least one of a horizontal direction or a vertical direction, and
wherein the coordinate of the control point of the neighboring block corresponds to a position of an upper left sample of the neighboring block and the coordiante of the one of the at least two control points of the current block corresponds to a position of an upper left sample of the current block.
2. The method of claim 1 , wherein the motion vector of the one among the at least two control points of the current block is derived based on modifying of the motion vector of the control point of the neighboring block or a reference block based on a difference between a size of the current block and, a size of the neighboring block or the reference block.
3. The method of claim 1 , wherein a size of the sub-block and/or a split type of the sub-block are determined based on the at leat two motion vectors of the at least two control points of the current block.
4. The method of claim 3 , wherein:
a width of the sub-block is determined based on a difference between a motion vector of an upper left control point of the current block and a motion vector of an upper right control point of the current block, and
a height of the sub-block is determined based on a difference between a motion vector of an upper left control point of the current block and a motion vector of a lower left control point of the current block.
5. The method of claim 1 , wherein a motion vector of a specific reference point in the sub-block is used as the motion vector of the sub-block.
6. The method of claim 5 , wherein in case of a sub-block comprising the control point or adjacent to the control point, a motion vector of the control point is used as the motion vector of the sub-block.
7. The method of claim 5 , wherein a motion vector of a plurality of reference points in the sub-block is used as the motion vector of the sub-block.
8. The method of claim 1 , wherein:
the prediction block is generated based on a motion vector of a single reference point, and
the generated prediction block is updated pixel-by-pixel based on the optical flow and a plurality of prediction blocks derived based on a motion vector of a plurality of reference points.
9. The method of claim 1 , wherein the optical flow is applied only for sub-blocks that do not include the control point or are not adjacent to the control point.
10. A method of encoding an image based on inter prediction, comprising steps of:
deriving, by a processor, at least two motion vectors of at least two control points of a current block;
splitting, by the processor, the current block into sub-blocks; deriving, by the processor, a motion vector of each of the sub-blocks based on the at least two motion vectors of the at least two control points of the current block;
generating, by the processor, a prediction block for each of the sub-blocks based on the motion vector of each of the sub-blocks; and
updating, by the processor, the prediction block for each of the sub-blocks pixel-by-pixel based on an optical flow,
wherein the at least two motion vectors of the at least two control points of the current block are derived based on a motion vector of a control point of a neighboring block, and
wherein a motion vector of one among the at least two control points of the current block is derived based on modifying of the motion vector of the control point of the neighboring block based on a difference between a coordinate of the control point of the neighboring block and a coordinate of one of the at least two control points of the current block, and a difference between two motion vectors of two control points of the neighboring block with respect to at least one of a horizontal direction or a vertical direction, and
wherein the coordinate of the control point of the neighboring block corresponds to a position of an upper left sample of the neighboring block and the coordinate of the one of the at least two control points of the current block corresponds to a position of an upper left sample of the current block.
11. A non-transitory computer-readable recording medium storing a bitstream generated by a method of claim 10 .