Apparatus for performing image coding on basis of ATMVP candidate

An image encoding method performed by an encoding apparatus, the method comprising:

• deriving a subblock based temporal merge candidate for a current block;
• deriving affine candidates for the current block;
• deriving a merge candidate list for the current block, wherein the merge candidate list includes the subblock based temporal merge candidate and the affine candidates;
• deriving prediction samples for the current block based on the merge candidate list;
• deriving residual information based on the prediction samples;
• and
• encoding image information including the residual information,
• wherein the subblock based temporal merge candidate is derived based on a motion vector of a left neighboring block of the current block,
• wherein deriving the subblock based temporal merge candidate comprises:
• deriving the motion vector of the left neighboring block of the current block,
• deriving corresponding subblocks in a collocated picture based on the motion vector,
• deriving subblock motion vectors of the corresponding subblocks, and
• deriving the subblock based temporal merge candidate based on the subblock motion vectors,
• wherein deriving the subblock based temporal merge candidate further comprises deriving a base motion vector based on a motion vector related to a below-right center position of the current block, and
• wherein, based on a motion vector of a corresponding subblock not being available, the base motion vector is used as the subblock motion vector of the corresponding subblock.

A transmission method of data for an image, the method comprising:

• obtaining a bitstream for the image, wherein the bitstream is generated based on deriving a subblock based temporal merge candidate for a current block,
• deriving affine candidates for the current block,
• deriving a merge candidate list for the current block, wherein the merge candidate list includes the subblock based temporal merge candidate and the affine candidates,
• deriving prediction samples for the current block based on the merge candidate list;
• deriving residual information based on the prediction samples, and
• encoding image information including the residual information;
• and
• transmitting the data comprising the bitstream,
• wherein the subblock based temporal merge candidate is derived based on a motion vector of a left neighboring block of the current block,
• wherein deriving the subblock based temporal merge candidate comprises:
• deriving the motion vector of the left neighboring block of the current block,
• deriving corresponding subblocks in a collocated picture based on the motion vector,
• deriving subblock motion vectors of the corresponding subblocks, and
• deriving the subblock based temporal merge candidate based on the subblock motion vectors,
• wherein deriving the subblock based temporal merge candidate further comprises deriving a base motion vector based on a motion vector related to a below-right center position of the current block, and
• wherein, based on a motion vector of a corresponding subblock not being available, the base motion vector is used as the subblock motion vector of the corresponding subblock.