Method and device for processing video signal using affine motion prediction

1. A method for decoding a video signal by a decoding apparatus, the method comprising:

obtaining residual information from a bitstream;

checking information on the affine motion prediction of a current block;

obtaining a merge candidate index based on the information on the affine motion prediction, wherein the merge candidate index indicates a merge candidate within a merge candidate list;

determining a motion vector for each subblock of a plurality of subblocks included in the current block based on the merge candidate index;

generating a prediction sample for the current block based on the motion vector for each subblock of the plurality of subblocks;

generating a residual sample for the current block based on the residual information; and

generating a reconstructed sample based on the prediction sample and the residual sample,

wherein the step of checking the information on the affine motion prediction of the current block further comprises

determining whether a width and a height of the current block satisfy a condition corresponding to the information on the affine motion prediction; and

obtaining the information on the affine motion prediction of the current block based on that the condition is satisfied,

wherein how to perform the affine motion prediction is determined based on the information on the affine motion prediction, and

wherein based on that the information on the affine motion prediction includes an affine merge mode, the condition is based on checking whether a width and a height of the current block is greater than or equal to 8.

2. The method of claim 1 ,

wherein the condition is satisfied based on (i) the current block has been encoded by a bi-prediction, and a width and a height of the current block is greater than or equal to a second reference value, or (ii) the current block has been encoded by a uni-prediction, and a width and a height of the current block is greater than or equal to a third reference value,

wherein the second reference value is greater than or equal to the width or the height of the subblock, the second reference value is greater than or equal to the third reference value, and the third reference value is greater than or equal to the width or the height of a subblock.

3. The method of claim 1 ,

wherein the condition is satisfied based on (i) the current block has been encoded by a bi-prediction, a product of a width and a height of the current block is greater than or equal to a fourth reference value, and the width and the height of the current block is greater than or equal to a fifth reference value, or (ii) the current block has been encoded by a uni-prediction, a product of the width and the height of the current block is greater than or equal to a sixth reference value, and the width and the height of the current block is greater than or equal to a seventh reference value,

wherein the fourth reference value is greater than or equal to the sixth reference value, and the sixth reference value is greater than or equal to a width or a height of a subblock.

4. A method for encoding a video signal by an encoding apparatus, the method comprising:

generating a merge candidate list of a current block;

selecting a merge candidate within the merge candidate list;

determining a motion vector for each subblock of a plurality of subblocks included in the current block based on motion information of the merge candidate;

generating information on an affine motion prediction of the current block;

generating a prediction sample for the current block based on the motion vector for each subblock of the plurality of subblocks;

generating a merge candidate index indicating the selected merge candidate;

generating residual information based on the prediction sample; and

encoding image information including the residual information to generate a bitstream,

wherein the step of generating information on the affine motion prediction of the current block further comprises

checking whether a width and a height of the current block is greater than or equal to 8; and

generating the information on the affine motion prediction of the current block based on the width and the height of the current block is greater than or equal to 8, wherein the information on the affine motion prediction includes an affine merge mode,

wherein how to perform the affine motion prediction is determined based on the information on the affine motion prediction.

5. A non-transitory computer-readable storage medium storing a bitstream generated by the method for encoding the video signal of claim 4 .

6. A transmission method of data for image, the transmission method comprising:

obtaining a bitstream, wherein the bitstream is generated by generating a merge candidate list of a current block, selecting a merge candidate within the merge candidate list, determining a motion vector for each subblock of a plurality of subblocks included in the current block based on motion information of the merge candidate, generating information on an affine motion prediction of the current block, generating a prediction sample for the current block based on the motion vector for each subblock of the plurality of subblocks, generating a merge candidate index indicating the selected merge candidate, generating residual information based on the prediction sample, and encoding image information including the residual information; and

transmitting the data comprising the bitstream,

wherein the step of generating information on the affine motion prediction of the current block further comprises

checking whether a width and a height of the current block is greater than or equal to 8; and

generating the information on the affine motion prediction of the current block based on the width and the height of the current block is greater than or equal to 8, wherein the information on the affine motion prediction includes an affine merge mode,

wherein how to perform the affine motion prediction is determined based on the information on the affine motion prediction.