Image coding method using history-based motion information and apparatus for the same
According to an embodiment disclosed in the present specification, a history-based motion vector prediction (HMVP) candidate set with respect to a current block may be derived based on a history, the HMVP candidate set may be updated or initialized according to a condition, and motion information of the current block may be derived based on the HMVP candidate set, through which inter prediction efficiency can be improved.
1. An image decoding method performed by a decoding apparatus, the method comprising:
dividing a current picture into a plurality of tiles;
deriving a history-based motion vector prediction (HMVP) candidate set for a current block;
configuring a motion information candidate list based on an HMVP candidate comprised in the HMVP candidate set;
deriving motion information of the current block based on the motion information candidate list;
deriving a reference picture index of the current block and a motion vector of the current block based on the motion information; and
generating prediction samples for the current block based on the motion vector and the reference picture index;
wherein a current block is for one of coding units (CUs) split from a coding tree unit (CTU);
wherein the HMVP candidate set is updated based on motion information of a previous block in a CTU row in a current tile, wherein the CTU row comprising the current block;
wherein for CTUs of the CTU row in the current tile, the HMVP candidate set is initialized only at a specific CTU among the CTUs of the CTU row in the current tile;
wherein the specific CTU is a firstly-ordered CTU among the CTUs of the CTU row in the current tile; and
wherein based on the current picture being divided into the plurality of tiles, the HMVP candidate set is initialized per each CTU row in each tile.
2. The method of claim 1 , wherein a slice data syntax includes a field for one or more CTUs in a slice; and
wherein information representing the specific CTU in which the HMVP candidate set is initialized is included in the slice data syntax.
3. The method of claim 1 , wherein based on the HMVP candidate set being initialized, the number of HMVP candidates belonging to the HMVP candidate set is set to 0.
4. The method of claim 1 , wherein based on the specific CTU being not the firstly-ordered CTU of the CTU row within a current picture but the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set is initialized at the specific CTU.
5. The method of claim 1 , wherein based on a current CTU including the current block being determined to be the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set includes an HMVP candidate derived based on motion information of a block processed earlier than the current block within the current CTU; and
based on a determination that the current CTU is not the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set includes a first HMVP candidate derived based on motion information of a block processed earlier than the current block within the current CTU and a second HMVP candidate derived based on motion information of a block processed earlier within a previous CTU of the current CTU of the CTU row within the current tile.
6. The method of claim 1 , wherein based on a merge mode being applied to the current block, the motion information candidate list is a merge candidate list, and the HMVP candidate belonging to the HMVP candidate set is included as a candidate of the merge candidate list; and
the HMVP candidate is indicated based on a merge index obtained from a bitstream among candidates belonging to the merge candidate list.
7. An image encoding method performed by an encoding apparatus, the method comprising:
dividing a current picture into a plurality of tiles;
deriving a history-based motion vector prediction (HMVP) candidate set for a current block;
constructing a motion information candidate list based on HMVP candidates belonging to the HMVP candidate set;
deriving motion information of the current block based on the motion information candidate list;
deriving a reference picture index of the current block and a motion vector of the current block based on the motion information; and
generating prediction samples for the current block based on the motion vector and the reference picture index;
wherein a current block is for one of coding units (CUs) split from a coding tree unit (CTU);
wherein the HMVP candidate set is updated based on motion information of a previous block in a CTU row in a current tile, wherein the CTU row comprising the current block;
wherein for CTUs of the CTU row in the current tile, the HMVP candidate set is initialized only at a specific CTU among the CTUs of the CTU row in the current tile;
wherein the specific CTU is a firstly-ordered CTU among the CTUs of the CTU row in the current tile; and
wherein based on the current picture being divided into the plurality of tiles, the HMVP candidate set is initialized per each CTU row in each tile.
8. The method of claim 7 , wherein a slice data syntax includes a field for one or more CTUs in a slice; and
wherein information representing the specific CTU in which the HMVP candidate set is initialized is included in the slice data syntax.
9. The method of claim 7 , wherein based on the specific CTU being not the firstly-ordered CTU of the CTU row within the current picture but the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set is initialized at the specific CTU.
10. The method of claim 7 , wherein based on the HMVP candidate set being initialized, the number of HMVP candidates belonging to the HMVP candidate set is set to 0.
11. The method of claim 7 ,
wherein based on a current CTU including the current block being determined to be the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set includes an HMVP candidate derived based on motion information of a block processed earlier than the current block within the current CTU; and
based on a determination that the current CTU is not the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set includes a first HMVP candidate derived based on motion information of a block processed earlier than the current block within the current CTU and a second HMVP candidate derived based on motion information of a block processed earlier within a previous CTU of the current CTU of the CTU row within the current tile.
12. The method of claim 7 , wherein based on a merge mode being applied to the current block, the motion information candidate list is a merge candidate list, and the HMVP candidate belonging to the HMVP candidate set is included as a candidate of the merge candidate list; and
a merge index included in the image information indicates the HMVP candidate among candidates belonging to the merge candidate list.
13. A non-transitory computer-readable digital storage medium storing bitstream generated by a method, the method comprising: performing dividing a current picture into a plurality of tiles; deriving a history-based motion vector prediction (HMVP) candidate set for a current block; constructing a motion information candidate list based on HMVP candidates belonging to the HMVP candidate set; deriving motion information of the current block based on the motion information candidate list; deriving a reference picture index of the current block and a motion vector of the current block based on the motion information; and generating prediction samples for the current block based on the motion vector and the reference picture index
wherein a current block is for one of coding units (CUs) split from a coding tree unit (CTU);
wherein the HMVP candidate set is updated based on motion information of a previous block in a CTU row in a current tile, wherein the CTU row comprising the current block;
wherein for CTUs of the CTU row in the current tile, the HMVP candidate set is initialized only at a specific CTU among the CTUs of the CTU row in the current tile;
wherein the specific CTU is a firstly-ordered CTU among the CTUs of the CTU row in the current tile; and
wherein based on the current picture being divided into the plurality of tiles, the HMVP candidate set is initialized per each CTU row in each tile.
14. The non-transitory computer-readable digital storage medium of claim 13 , wherein a slice data syntax includes a field for one or more CTUs in a slice; and
wherein information representing the specific CTU in which the HMVP candidate set is initialized is included in the slice data syntax.
15. The non-transitory computer-readable digital storage medium of claim 13 , wherein based on the HMVP candidate set being initialized, the number of HMVP candidates belonging to the HMVP candidate set is set to 0.
16. The non-transitory computer-readable digital storage medium of claim 13 , wherein based on the specific CTU being not the firstly-ordered CTU of the CTU row within a current picture but the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set is initialized at the specific CTU.
17. The non-transitory computer-readable digital storage medium of claim 13 , wherein based on a current CTU including the current block being determined to be the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set includes an HMVP candidate derived based on motion information of a block processed earlier than the current block within the current CTU; and
based on a determination that the current CTU is not the firstly-ordered CTU of the CTU row within the current tile, the HMVP candidate set includes a first HMVP candidate derived based on motion information of a block processed earlier than the current block within the current CTU and a second HMVP candidate derived based on motion information of a block processed earlier within a previous CTU of the current CTU of the CTU row within the current tile.
18. The non-transitory computer-readable digital storage medium of claim 13 , wherein based on a merge mode being applied to the current block, the motion information candidate list is a merge candidate list, and the HMVP candidate belonging to the HMVP candidate set is included as a candidate of the merge candidate list; and
the HMVP candidate is indicated based on a merge index obtained from a bitstream among candidates belonging to the merge candidate list.