Method and device for processing video signal by using affine motion
Disclosed are a method for processing a video signal by using an affine motion prediction and an apparatus thereof. A method for processing a video signal according to the present disclosure may include: adding, to an affine candidate list, an affine coded block coded in an affine prediction mode among neighbor blocks of a current block; obtaining a syntax element indicating a candidate used for the affine motion prediction of the current block in the affine candidate list; deriving a control point motion vector predictor of the current block based on an affine motion model of the candidate indicated by the syntax element; deriving a control point motion vector of the current block by adding a control point motion vector difference to the control point motion vector predictor; and generating a prediction block of the current block by using the control point motion vector of the current block.
1. An apparatus for decoding a video signal, comprising:
a memory configured to store the video signal; and
a processor coupled with the memory,
wherein the processor is configured to:
determine a block coded in an affine prediction mode among neighbor blocks of a current block as an affine candidate based on that the block having a same reference picture as a reference picture of the current block;
obtain a syntax element related to an affine candidate used for the affine motion prediction of the current block among affine candidates;
derive a control point motion vector predictor of the current block based on the affine candidate related to the syntax element;
derive a control point motion vector of the current block based on a control point motion vector difference and the control point motion vector predictor;
generate prediction samples of the current block based on the control point motion vector of the current block; and
generate reconstructed samples of the current block based on the prediction samples of the current block,
wherein for determining of the block, the processor is further configured to:
group the neighbor blocks of the current block into a first group and a second group; and
search the block coded in the affine prediction mode based on a predefined order in each of the first group and the second group.
2. The apparatus of claim 1 , wherein for determining of the block, the processor is further configured to determine a predefined maximum number of blocks coded in the affine prediction mode as the affine candidates, and
wherein the predefined maximum number is two.
3. The apparatus of claim 1 , wherein for determining of the block, the processor is further configured to:
search a valid affine coded block among the blocks having the same reference picture as the reference picture of the current block in the first group according to a predefined order, and
search a valid affine coded block among the blocks having the same reference picture as the reference picture of the current block in the top group according to a predefined order.
4. The apparatus of claim 1 , wherein for determining of the block, the processor is further configured to determine an affine candidate scaled based on a picture order count between reference pictures when there is no affine coded block among the neighbor blocks of the current block.
5. The apparatus of claim 1 , wherein for determining of the block, the processor is further configured to determine 0 or 1 block coded in the affine prediction mode in each group as the affine candidate.
6. An apparatus for encoding a video signal, comprising:
a memory configured to store the video signal; and
a processor coupled with the memory,
wherein the processor is configured to:
determine a block coded in an affine prediction mode among neighbor blocks of a current block as an affine candidate based on that the block having a same reference picture as a reference picture of the current block;
select an affine candidate used for the affine motion prediction of the current block among affine candidates;
derive a control point motion vector predictor of the current block based on the selected affine candidate;
derive a control point motion vector of the current block based on a control point motion vector difference and the control point motion vector predictor;
generate prediction samples of the current block based on the control point motion vector of the current block;
generate residual samples of the current block based on the prediction samples; and
generate a syntax element related to the selected affine candidate among the affine candidates,
wherein for determining of the block further includes:
group the neighbor blocks of the current block into a first group and a second group; and
search the block coded in the affine prediction mode based on a predefined order in each of the first group and the second group.
7. The apparatus of claim 6 , wherein for determining of the block the processor is further configured to determine a predefined maximum number of blocks coded in the affine prediction mode as the affine candidates, and
wherein the predefined maximum number is two.
8. The apparatus of claim 6 , wherein for determining of the block, the processor is further configured to
search a valid affine coded block among the blocks having the same reference picture as the reference picture of the current block in the first group according to a predefined order, and
search a valid affine coded block among the blocks having the same reference picture as the reference picture of the current block in the top group according to a predefined order.
9. The apparatus of claim 6 , wherein for determining of the block the processor is further configured to determine 0 or 1 block coded in the affine prediction mode in each group as the affine candidate.
10. An apparatus of transmitting data for an image, comprising:
a processor configured to obtain a bitstream for the image; and
a transmitter configured to transmit the data comprising the bitstream,
wherein the processor is configured to:
obtain the bitstream for the image; and
transmit the data comprising the bitstream,
wherein, for obtaining the bitstream, the processor is configured to:
determine a block coded in an affine prediction mode among neighbor blocks of a current block as an affine candidate based on that the block having a same reference picture as a reference picture of the current block;
select an affine candidate used for the affine motion prediction of the current block among affine candidates;
derive a control point motion vector predictor of the current block based on the selected affine candidate;
derive a control point motion vector of the current block based on a control point motion vector difference and the control point motion vector predictor;
generate prediction samples of the current block based on the control point motion vector of the current block;
generate residual samples of the current block based on the prediction samples; and
generate a syntax element related to the selected affine candidate among the affine candidates,
wherein for determining of the block further includes:
group the neighbor blocks of the current block into a first group and a second group; and
search the block coded in the affine prediction mode based on a predefined order in each of the first group and the second group.