Image encoding/decoding method and apparatus, and method of transmitting bitstream using sequence parameter set including information on maximum number of merge candidates
An image encoding/decoding method and apparatus are provided. An image decoding method according to the present disclosure is performed by an image decoding apparatus. The image decoding method comprises constructing a merge candidate list for a current block based on a prediction mode of the current block, deriving motion information of the current block based on the merge candidate list, and generating a prediction block of the current block based on the motion information. Information on a maximum number of merge candidates included in the merge candidate list may be obtained through a sequence parameter set, and, based on the prediction mode being a subblock-based merge mode, the maximum number of merge candidates may be determined based on whether an affine mode is available for the current block.
1. An image decoding method performed by an image decoding apparatus, the image decoding method comprising:
constructing a candidate list for a current block based on a prediction mode of the current block;
deriving motion information of the current block based on the candidate list; and
generating a prediction block of the current block based on the motion information,
wherein information on a maximum number of candidates included in the candidate list includes information on a maximum number of subblock merge candidates, information on a maximum number of merge candidates, information on a maximum number of IBC (intra block copy) candidates and information on a maximum number of GPM (geometric partitioning mode) candidates,
wherein, based on the prediction mode being a subblock-based merge mode, the maximum number of subblock merge candidates is determined based on whether an affine mode is available for the current block,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode being available, the maximum number of subblock merge candidates is determined based on the information on the maximum number of subblock merge candidates,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode not being available, the maximum number of subblock merge candidates is determined as 1 based on a subblock-based temporal motion vector predictor (TMVP) mode being available for the current block and a temporal motion vector predictor (TMVP) mode being available for the current block,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode not being available, the maximum number of subblock merge candidates is determined as 0 based on one of the subblock-based TMVP mode and the TMVP mode not being available for the current block,
wherein whether the subblock-based TMVP mode is available or not is determined based on a first flag obtained through the sequence parameter set,
wherein whether the TMVP mode is available or not is determined based on a second flag obtained through a picture header,
wherein the information on the maximum number of the candidates included in the candidate list is obtained through a sequence parameter set, and
wherein, in response to the subblock-based TMVP mode being available, a value of the information on the maximum number of subblock merge candidates has a range from 0 to 4 and the maximum number of subblock merge candidates have a range from 1 to 5.
2. An image encoding method performed by an image encoding apparatus, the image encoding method comprising:
constructing a candidate list for a current block based on a prediction mode of the current block;
deriving motion information of the current block based on the candidate list; and
encoding the motion information and information on a maximum number of candidates included in the candidate list,
wherein the information on the maximum number of the candidates included in the candidate list includes information on a maximum number of subblock merge candidates, information on a maximum number of merge candidates, information on a maximum number of IBC (intra block copy) candidates and information on a maximum number of GPM (geometric partitioning mode) candidates,
wherein, based on the prediction mode being a subblock-based merge mode, the maximum number of subblock merge candidates is determined based on whether an affine mode is available for the current block,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode being available, the maximum number of subblock merge candidates is determined based on the information on the maximum number of subblock merge candidates,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode not being available, the maximum number of subblock merge candidates is determined as 1 based on a subblock-based temporal motion vector predictor (TMVP) mode being available for the current block and a temporal motion vector predictor (TMVP) mode being available for the current block,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode not being available, the maximum number of subblock merge candidates is determined as 0 based on one of the subblock-based TMVP mode and the TMVP mode not being available for the current block,
wherein a first flag specifying whether the subblock-based TMVP mode is available or not is encoded in the sequence parameter set,
wherein a second flag specifying whether the TMVP mode is available or not is encoded in a picture header,
wherein the information on the maximum number of the candidates included in the candidate list is obtained through a sequence parameter set, and
wherein, in response to the subblock-based TMVP mode being available, a value of the information on the maximum number of subblock merge candidates has a range from 0 to 4 and the maximum number of subblock merge candidates have a range from 1 to 5.
3. A method for transmitting a bitstream generated by an image encoding method, the image encoding method comprising:
constructing a candidate list for a current block based on a prediction mode of the current block;
deriving motion information of the current block based on the candidate list; and
encoding the motion information and information on a maximum number of candidates included in the candidate list,
wherein the information on the maximum number of the candidates included in the candidate list includes information on a maximum number of subblock merge candidates, information on a maximum number of merge candidates, information on a maximum number of IBC (intra block copy) candidates and information on a maximum number of GPM (geometric partitioning mode) candidates,
wherein, based on the prediction mode being a subblock-based merge mode, the maximum number of subblock merge candidates is determined based on whether an affine mode is available for the current block,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode being available, the maximum number of subblock merge candidates is determined based on the information on the maximum number of subblock merge candidates,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode not being available, the maximum number of subblock merge candidates is determined as 1 based on a subblock-based temporal motion vector predictor (TMVP) mode being available for the current block and a temporal motion vector predictor (TMVP) mode being available for the current block,
wherein, based on the prediction mode being the subblock-based merge mode and the affine mode not being available, the maximum number of subblock merge candidates is determined as 0 based on one of the subblock-based TMVP mode and the TMVP mode not being available for the current block,
wherein a first flag specifying whether the subblock-based TMVP mode is available or not is encoded in the sequence parameter set,
wherein a second flag specifying whether the TMVP mode is available or not is encoded in a picture header,
wherein the information on the maximum number of the candidates included in the candidate list is obtained through a sequence parameter set, and
wherein, in response to the subblock-based TMVP mode being available, a value of the information on the maximum number of subblock merge candidates has a range from 0 to 4 and the maximum number of subblock merge candidates have a range from 1 to 5.