Image processing method based on inter prediction mode, and device therefor

An apparatus of encoding an image, comprising:

• a memory configured to store the image;
• and
• a processor coupled with the memory,
• wherein the processor is configured to:
• based on that a reference picture of a spatial neighboring block around a current block is the same as one pre-defined reference picture among reference pictures included in a reference picture list, derive a collocated block of the current block in the one pre-defined reference picture using a motion vector of the spatial neighboring block;
• derive motion vectors of sub-blocks in the current block based on a motion vector of the collocated block;
• generate prediction samples of the current block based on the motion vectors of the sub-blocks;
• generate residual samples of the current block based on the prediction samples;
• and
• generate a reference index indicating the one pre-defined reference picture, wherein the one pre-defined reference picture is defined in a slice header.

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:
• based on that a reference picture of a spatial neighboring block around a current block is the same as one pre-defined reference picture among reference pictures included in a reference picture list, derive a collocated block of the current block in the one pre-defined reference picture using a motion vector of the spatial neighboring block;
• derive motion vectors of sub-blocks in the current block based on a motion vector of the collocated block;
• generate prediction samples of the current block based on the motion vectors of the sub-blocks;
• generate residual samples of the current block based on the prediction samples;
• and
• generate a reference index indicating the one pre-defined reference picture, wherein the one pre-defined reference picture is defined in a slice header.