Method and apparatus for video coding using intra prediction based on subblock partitioning
A video coding method and a device using subblock partition-based intra prediction are disclosed. The video coding method and device perform intra prediction of the subblocks by eliminating unnecessary parsing of the intra-prediction mode or revising the prediction mode or reconstruction order when intra-predicting subblocks divided from the current block.
1 . A method performed by a video decoding device for intra predicting a current block, the method comprising:
decoding, from a bitstream, a subblock partition application flag that indicates whether to apply subpartitioning to the current block; and
performing an intra prediction of the current block in accordance with the subblock partition application flag,
wherein performing the intra prediction comprises, when the subblock partition application flag is true:
decoding subpartition information from the bitstream;
generating subblocks by partitioning the current block by using the subpartition information;
decoding an intra prediction mode of the current block from the bitstream;
determining, for each subblock, an intra prediction mode based on the intra prediction mode of the current block;
determining a reconstruction order of the subblocks; and
generating prediction signals of the subblocks by performing an intra prediction on the subblocks by using the intra prediction modes and the reconstruction order of the subblocks, and
wherein determining the reconstruction order of the subblocks comprises at least one of:
(i) determining, when the current block is horizontally partitioned and the intra prediction mode of the current block has a direction between a left direction and a bottom-left direction, the reconstruction order of the subblocks such that the subblocks are reconstructed in an order from a bottom sub-block to a top sub-block;
(ii) determining, when the current block is vertically partitioned and the intra prediction mode of the current block has a direction between a right direction and a top-right direction, the reconstruction order of the subblocks such that the subblocks are reconstructed in an order from a right sub-block to a left sub-block; or
(iii) a combination thereof.
2 . The method of claim 1 , wherein the subpartition information comprises:
a subblock partition direction flag and an index of a partition mode,
wherein the partition mode indicates sizes of K equal or unequal subblocks, and
wherein the index of the partition mode indicates one partition mode from a list comprising a plurality of preset partition modes.
3 . The method of claim 2 , wherein generating the subblocks comprises:
determining a horizontal partitioning or a vertical partitioning based on the subblock partition direction flag;
determining the sizes of the subblocks based on the index of the partition mode; and
partitioning the current block based on a determination between horizontal and vertical partitioning and further based on sizes of the subblocks.
4 . The method of claim 3 , wherein performing the intra prediction comprises:
upon determining the horizontal partitioning, when the subblocks include at least one subblock having an aspect ratio greater than 1, skipping a revision of a reconstruction order of the subblocks for a preset prediction mode.
5 . The method of claim 3 , wherein generating predicted signals comprises:
upon determining the horizontal partitioning, when a previously reconstructed subblock has a height that is greater than N pixels (wherein N is a positive integer), performing the intra prediction of the subblocks by using reconstructed pixels of the previously reconstructed subblock.
6 . The method of claim 3 , wherein generating predicted signals comprises:
upon determining the horizontal partitioning, performing the intra prediction of the subblocks by using reconstructed pixels located downward of each subblock.
7 . The method of claim 3 , wherein performing the intra prediction comprises:
upon determining the vertical partitioning, when the subblocks include at least one subblock having an aspect ratio greater than 1, skipping a revision of a reconstruction order of the subblocks for a preset prediction mode.
8 . The method of claim 3 , wherein generating the predicted signals comprises:
upon determining the vertical partitioning, performing the intra prediction of the subblocks by using reconstructed pixels located rightward of each subblock.
9 . The method of claim 1 , further comprising:
determining a reconstruction order of the subblocks based on the intra prediction mode and the aspect ratio of each subblock.
10 . The method of claim 1 , wherein performing the intra prediction comprises, when the subblock partition application flag is false:
decoding the intra prediction mode of the current block from the bitstream; and
generating predicted signals of the current block by performing an intra prediction on the current block by using the intra prediction mode.
11 . A method performed by a video encoding device for intra predicting a current block, the method comprising:
determining whether to apply subpartitioning to a current block;
encoding a subblock partition application flag that indicates whether to apply subpartitioning to the current block; and
performing an intra prediction of the current block based on whether the subpartitioning is applied to the current block,
wherein performing the intra prediction comprises, when the subpartitioning is applied to the current block:
generating subblocks by partitioning the current block;
determining an intra prediction mode of the current block;
determining a reconstruction order of the subblocks; and
generating prediction signals of the subblocks by performing an intra prediction on the subblocks by using the intra prediction modes and the reconstruction order of the subblocks,
wherein determining the reconstruction order of the subblocks comprises at least one of:
(i) determining, when the current block is horizontally partitioned and the intra prediction mode of the current block has a direction between a left direction and a bottom-left direction, the reconstruction order of the subblocks such that the subblocks are reconstructed in an order from a bottom sub-block to a top sub-block;
(ii) determining, when the current block is vertically partitioned and the intra prediction mode of the current block has a direction between a right direction and a top-right direction, the reconstruction order of the subblocks such that the subblocks are reconstructed in an order from a right sub-block to a left sub-block; or
(iii) a combination thereof.
12 . The method of claim 11 , wherein performing the intra prediction comprises, when the subblock partition application flag is false:
determining the intra prediction mode of the current block; and
generating predicted signals of the current block by performing an intra prediction on the current block by using the intra prediction mode.
13 . A method for transmitting a bitstream containing encoded video data, the method comprising:
generating the bitstream for a current block in an image; and
transmitting the bitstream,
wherein generating the bitstream for the image comprises:
determining whether to apply subpartitioning to the current block;
encoding a subblock partition application flag that indicates whether to apply subpartitioning to the current block; and
performing an intra prediction of the current block based on whether the subpartitioning is applied to the current block,
wherein performing the intra prediction comprises, when the subpartitioning is applied to the current block:
generating subblocks by partitioning the current block;
determining an intra prediction mode of the current block;
determining a reconstruction order of the subblocks; and
generating prediction signals of the subblocks by performing an intra prediction on the subblocks by using the intra prediction modes and the reconstruction order of the subblocks,
wherein determining the reconstruction order of the subblocks comprises at least one of:
(i) determining, when the current block is horizontally partitioned and the intra prediction mode of the current block has a direction between a left direction and a bottom-left direction, the reconstruction order of the subblocks such that the subblocks are reconstructed in an order from a bottom sub-block to a top sub-block;
(ii) determining, when the current block is vertically partitioned and the intra prediction mode of the current block has a direction between a right direction and a top-right direction, the reconstruction order of the subblocks such that the subblocks are reconstructed in an order from a right sub-block to a left sub-block; or
(iii) a combination thereof.