Image decoding method and device therefor
An image decoding method performed by a decoding device, according to the present disclosure, comprises the steps of: deriving an intra block copy (IBC) mode as a prediction mode of a current block; deriving one or more block vectors and/or scaling information for the IBC mode; deriving a revised reference block for the current block by using the one or more block vectors and/or the scaling information in a current picture; deriving a prediction sample of the current block on the basis of the revised reference block; and generating a reconstructed picture on the basis of the prediction sample.
1 . An image decoding method that is performed by a decoding apparatus, the image decoding method comprising:
deriving an intra block copy (IBC) mode as a prediction mode of a current block;
deriving a revised reference block for the current block in a current picture;
deriving a prediction sample of the current block based on the revised reference block; and
generating a reconstructed picture based on the prediction sample,
wherein whether affine prediction is applied to the current block is determined,
wherein, based on the affine prediction being applied to the current block, block vector information and an affine angle index of the current block are obtained through a bitstream, and
wherein the revised reference block for the current block is derived based on the block vector information and the affine angle index of the current block.
2 . The image decoding method of claim 1 ,
wherein, based on the affine prediction being applied to the current block, control point motion vectors (CPMVs) of the current block are derived, and
wherein the revised reference block for the current block is derived based on the CPMVs.
3 . The image decoding method of claim 2 , wherein information on the CPMV including motion vector prediction (MVP) index information of the current block is obtained through a bitstream,
an MVP list of the current block is constructed, and
the CPMVs of the current block are derived based on MVP candidates in the MVP list indicated by the MVP index information.
4 . The image decoding method of claim 1 ,
wherein a subblock motion vector of the current block is derived based on the block vector information and a deformation angle indicated by the affine angle index, and
wherein the revised reference block for the current block is derived based on the subblock motion vector.
5 . The image decoding method of claim 4 , wherein the subblock motion vector is derived based on an Equation below,
[
cos
θ
-
sin
θ
sin
θ
cos
θ
]
[
x
y
]
,
where θ denotes the deformation angle, x denotes an x coordinate of a center position of a reference block indicated by the block vector information, and y denotes y coordinate of the center position of the reference block indicated by the block vector information.
6 . The image decoding method of claim 1 ,
wherein a block vector of the current block is derived based on the block vector information, and
wherein the revised reference block for the current block is derived based on a reference block, which is derived based on the block vector, for the current block in the current picture, and a deformation angle indicated by the affine angle index.
7 . The image decoding method of claim 1 ,
wherein, based on scaling being applied to the current block, block vector information and a scale index of the current block are obtained through a bitstream,
wherein a block vector of the current block is derived based on the block vector information,
wherein a reference block for the current block in the current picture is derived based on the block vector, and
wherein the revised reference block for the current block is derived by scaling the reference block based on the scale index.
8 . The image decoding method of claim 7 , wherein, based on the scale index indicating scale-up, the revised reference block is derived using an interpolation filter for samples of the reference block.
9 . The image decoding method of claim 7 , wherein, based on the scale index indicating scale-up, the revised reference block is derived by padding a sample of the reference block.
10 . The image decoding method of claim 7 , wherein, based on the scale index indicating scale-down, the revised reference block is derived using a decimation filter for samples of the reference block.
11 . The image decoding method of claim 7 , wherein, based on the scale index indicating scale-down, the revised reference block is derived by sub-sampling a sample of the reference block.
12 . An image encoding method that is performed by an encoding apparatus, the image encoding method comprising:
deriving an intra block copy (IBC) mode as a prediction mode of a current block;
deriving a revised reference block for the current block in a current picture;
deriving a prediction sample of the current block based on the revised reference block; and
encoding image information including prediction mode information of the current block,
wherein whether affine prediction is applied to the current block is determined,
wherein, based on the affine prediction being applied to the current block, block vector information and an affine angle index of the current block are derived, and
wherein the revised reference block for the current block is derived based on the block vector information and the affine angle index of the current block.
13 . The image encoding method of claim 12 ,
wherein, based on the affine prediction being applied to the current block, control point motion vectors (CPMVs) of the current block are derived,
wherein the revised reference block for the current block is derived based on the CPMVs, and
information on the CPMV including MVP index information of the current block is encoded.
14 . A digital storage medium in which a bitstream including the prediction mode information encoded by the image encoding method of claim 12 is stored.
15 . A transmission method of data for an image, the transmission method comprising:
obtaining a bitstream of image information including prediction mode information of a current block; and
transmitting the data including the bitstream of the image information which includes the prediction mode information,
wherein the prediction mode information is encoded by deriving an intra block copy (IBC) mode as a prediction mode of the current block, deriving a revised reference block for the current block in a current picture, and deriving a prediction sample of the current block based on the revised reference block,
wherein whether affine prediction is applied to the current block is determined,
wherein, based on the affine prediction being applied to the current block, block vector information and an affine angle index of the current block are derived, and
wherein the revised reference block for the current block is derived based on the block vector information and the affine angle index of the current block.