Method for predicting subblock-based temporal motion vector and apparatus therefor
An image decoding method performed by a decoding apparatus according to the present disclosure includes determining whether to use an advanced temporal motion vector predictor (ATMVP) candidate of sub-block unit for a current block, specifying a corresponding block corresponding to the current block in a reference picture based on a motion vector for a spatial neighboring block of the current block when the ATMVP candidate of the sub-block unit is used, deriving the ATMVP candidate of the sub-block unit for the current block based on motion vectors of sub-block unit of the corresponding block, constructing a merge candidate list including the ATMVP candidate of the sub-block unit for the current block, generating prediction samples of the current block by deriving motion vectors of the sub-block unit for the current block based on the merge candidate list and reconstructing a current picture based on the prediction samples of the current block.
1. A decoding apparatus for image decoding, the decoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
obtain a flag indicating whether to use a subblock-based temporal motion vector predictor (SbTMVP) candidate from a bitstream,
determine whether to use the SbTMVP candidate of a sub-block unit for a current block based on the flag;
derive the SbTMVP candidate of the sub-block unit for the current block based on motion vectors of corresponding sub-blocks related to current sub-blocks split from the current block;
construct a merge candidate list including the SbTMVP candidate of the sub-block unit for the current block;
generate prediction samples of the current block by deriving motion vectors of the sub-block unit for the current block based on the merge candidate list; and
reconstruct a current picture based on the prediction samples of the current block,
wherein the corresponding sub-blocks are located in a reference picture and the motion vectors of the corresponding sub-blocks are derived based on a motion vector of a left neighboring block for the current block, and
wherein the SbTMVP candidate of the sub-block unit is determined not to be used for the current block based on a size of the current block being smaller than a fixed sub-block size which is pre-defined as a minimum sub-block size of 8×8.
2. An encoding apparatus for image encoding, the encoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
determine whether to use a subblock-based temporal motion vector predictor (SbTMVP) candidate of a sub-block unit for a current block;
generate a flag indicating whether to use the SbTMVP candidate of the sub-block unit for the current block;
derive the SbTMVP candidate of the sub-block unit for the current block based on motion vectors of corresponding sub-blocks related to current sub-blocks split from the current block;
construct a merge candidate list including the SbTMVP candidate of the sub-block unit for the current block;
generate a candidate index indicating a candidate applied to the current block among the candidates in the merge candidate list; and
encode image information including the flag and the candidate index to output a bitstream,
wherein the corresponding sub-blocks are located in a reference picture and the motion vectors of the corresponding sub-blocks are derived based on a motion vector of a left neighboring block for the current block, and
wherein the SbTMVP candidate of the sub-block unit is determined not to be used for the current block based on a size of the current block being smaller than a fixed sub-block size which is pre-defined as a minimum sub-block size of 8×8.
3. An apparatus for transmitting data for an image, the apparatus comprising:
at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on determining whether to use a subblock-based temporal motion vector predictor (SbTMVP) candidate of a sub-block unit for a current block, generating a flag indicating whether to use the SbTMVP candidate of the sub-block unit for the current block, deriving the SbTMVP candidate of the sub-block unit for the current block based on motion vectors of corresponding sub-blocks related to current sub-blocks split from the current block, constructing a merge candidate list including the SbTMVP candidate of the sub-block unit for the current block, generating a candidate index indicating a candidate applied to the current block among the candidates in the merge candidate list, and encoding image information including the flag and the candidate index; and
a transmitter configured to transmit the data comprising the bitstream,
wherein the corresponding sub-blocks are located in a reference picture and the motion vectors of the corresponding sub-blocks are derived based on a motion vector of a left neighboring block for the current block, and
wherein the SbTMVP candidate of the sub-block unit is determined not to be used for the current block based on a size of the current block being smaller than a fixed sub-block size which is pre-defined as a minimum sub-block size of 8×8.