Method for processing image on basis of inter-prediction mode and device therefor

An apparatus for encoding a video signal based on an inter prediction mode, comprising:

• a memory configured to store the video signal;
• and
• a processor coupled with the memory,
• wherein the processor is configured to:
• generate a merge candidate list by using a spatial neighboring block and a temporal neighboring block of a current block, based on that a merge mode is applied to the current block;
• generate a merge index indicating a candidate to be used for an inter prediction of the current block in the merge candidate list;
• derive a motion vector of each subblocks included in the current block based on a motion vector of the candidate indicated by the merge index;
• generate a prediction block of the current block based on the motion vector of each subblocks;
• generate a residual block of the current block based on the prediction block;
• and
• perform transform on the residual block,
• wherein the processor is further configured to add a block which is located in a collocated picture of the current block and specified by a motion vector of the spatial neighboring block to the merge candidate list as the temporal neighboring block, based on that a width and a height of the current block is greater than or equal to a pre-defined size.

A non-transitory decoder-readable storage medium storing encoded picture information generated by performing the steps of:

• generating a merge candidate list by using a spatial neighboring block and a temporal neighboring block of a current block, based on that a merge mode is applied to the current block;
• generating a merge index indicating a candidate to be used for an inter prediction of the current block in the merge candidate list;
• deriving a motion vector of each subblocks included in the current block based on a motion vector of the candidate indicated by the merge index;
• generating a prediction block of the current block based on the motion vector of each subblocks;
• generating a residual block of the current block based on the prediction block;
• and
• performing transform on the residual block,
• wherein a block which is located in a collocated picture of the current block and specified by a motion vector of the spatial neighboring block is added to the merge candidate list as the temporal neighboring block, based on that a width and a height of the current block is greater than or equal to a pre-defined size.