Inter prediction method and apparatus in video coding system
A video decoding method performed by a decoding apparatus includes the steps of: deriving control points (CP) for a current block; acquiring movement vectors for the CPs; deriving a sample unit movement vector in the current block on the basis of the acquired movement vectors; and deriving a prediction sample for the current block on the basis of the sample unit movement vector. According to the present invention, it is possible to effectively perform, through sample unit motion vectors, inter-prediction not only in a case where an image in the current block is plane-shifted but also in a case where there are various image distortions.
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:
derive motion vectors for control points (CPs) for a current block;
derive a motion vector for the current block based on the motion vectors for the CPs;
perform a prediction for the current block based on the motion vector for the current block; and
generate a reconstructed block for the current block based on a result of the prediction for the current block,
wherein the CPs includes a first CP, a second CP and a third CP, wherein the first CP is for a top-left corner of the current block, the second CP is for a top-right corner of the current block and the third CP is for bottom-left corner of the current block,
wherein the motion vectors for the CPs include a first motion vector for the first CP, a second motion vector for the second CP and a third motion vector for the third CP,
wherein the first motion vector is derived based on a firstly-checked available block according to a first predefined priority order in a first block group,
wherein the first block group comprises a top-left corner neighboring block of the current block, a first top neighboring block which is leftmost block among blocks adjacent to an upper side of the current block and a first left neighboring block which is an uppermost block among blocks adjacent to a left side of the current block,
wherein the second motion vector is derived based on a firstly-checked available block according to a second predefined priority order in a second block group,
wherein the second block group comprises a top-right corner neighboring block of the current block and a second top neighboring block which is a rightmost block among the blocks adjacent to the upper side of the current block,
wherein the third motion vector is derived based on a firstly-checked available block according to a third predefined priority order in a third block group, and
wherein the third block group comprises a bottom-left corner neighboring block of the current block and a second left neighboring block which is a lowermost block among the blocks adjacent to the left side of the current block.
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:
derive motion vectors for control points (CPs) for a current block;
derive a motion vector for the current block based on the motion vectors for the CPs;
perform a prediction for the current block based on the motion vector for the current block; and
encode video information including information on the prediction for the current block,
wherein the CPs includes a first CP, a second CP and a third CP, wherein the first CP is for a top-left corner of the current block, the second CP is for a top-right corner of the current block and the third CP is for bottom-left corner of the current block,
wherein the motion vectors for the CPs include a first motion vector for the first CP, a second motion vector for the second CP and a third motion vector for the third CP,
wherein the first motion vector is derived based on a firstly-checked available block according to a first predefined priority order in a first block group,
wherein the first block group comprises a top-left corner neighboring block of the current block, a first top neighboring block which is leftmost block among blocks adjacent to an upper side of the current block and a first left neighboring block which is an uppermost block among blocks adjacent to a left side of the current block,
wherein the second motion vector is derived based on a firstly-checked available block according to a second predefined priority order in a second block group,
wherein the second block group comprises a top-right corner neighboring block of the current block and a second top neighboring block which is a rightmost block among the blocks adjacent to the upper side of the current block,
wherein the third motion vector is derived based on a firstly-checked available block according to a third predefined priority order in a third block group, and
wherein the third block group comprises a bottom-left corner neighboring block of the current block and a second left neighboring block which is a lowermost block among the blocks adjacent to the left side of the current block.
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 deriving motion vectors for control points (CPs) for a current block, deriving a motion vector for the current block based on the motion vectors for the CPs, performing a prediction for the current block based on the motion vector for the current block, and encoding video information including information on the prediction for the current block; and
transmitting the data comprising the bitstream,
wherein the CPs includes a first CP, a second CP and a third CP, wherein the first CP is for a top-left corner of the current block, the second CP is for a top-right corner of the current block and the third CP is for bottom-left corner of the current block,
wherein the motion vectors for the CPs include a first motion vector for the first CP, a second motion vector for the second CP and a third motion vector for the third CP,
wherein the first motion vector is derived based on a firstly-checked available block according to a first predefined priority order in a first block group,
wherein the first block group comprises a top-left corner neighboring block of the current block, a first top neighboring block which is leftmost block among blocks adjacent to an upper side of the current block and a first left neighboring block which is an uppermost block among blocks adjacent to a left side of the current block,
wherein the second motion vector is derived based on a firstly-checked available block according to a second predefined priority order in a second block group,
wherein the second block group comprises a top-right corner neighboring block of the current block and a second top neighboring block which is a rightmost block among the blocks adjacent to the upper side of the current block,
wherein the third motion vector is derived based on a firstly-checked available block according to a third predefined priority order in a third block group, and
wherein the third block group comprises a bottom-left corner neighboring block of the current block and a second left neighboring block which is a lowermost block among the blocks adjacent to the left side of the current block.