Image decoding method/apparatus, image encoding method/apparatus, and recording medium storing bitstream
The present invention provides an image encoding method and an image decoding method. An image decoding method according to the present invention, for decoding an image by decoder-side motion information derivation, comprises the steps of: checking, from among a plurality of motion information derivation types, the motion information derivation type applied to the current block: and deriving motion information of the current block according to the checked motion information derivation type, wherein different motion information compensation techniques are applicable according to the motion information derivation type.
1. A method of decoding an image, comprising:
deriving initial motion information of a current block based on a merge candidate list including a plurality of merge candidates;
deriving delta motion information of the current block based on a sum of absolute difference (SAD) list for a search area, the SAD list including a plurality of SAD candidates;
updating the initial motion information of the current block based on the delta motion information; and
performing inter prediction on the current block based on the updated initial motion information,
wherein deriving the delta motion information is performed based on a comparison result between a reference SAD candidate and a predetermined threshold,
wherein the reference SAD candidate is representative of a SAD candidate corresponding to a non-directional offset, and
wherein when the reference SAD candidate is greater than or equal to the predetermined threshold, deriving the delta motion information comprises:
identifying a SAD candidate having a minimum value among the SAD candidates belonging to the SAD list; and
determining the delta motion information based on an offset corresponding to the identified SAD candidate.
2. The method of claim 1 , wherein the search area is determined as an area including at least one of a reference block specified by the initial motion information or an adjacent area of the reference block, and
wherein the adjacent area is an area extended by N sample lines from a boundary of the reference block.
3. The method of claim 1 , wherein the SAD candidate is determined by a SAD value between a L0 block and a L1 block, and
wherein the L0 block is determined based on a position of a L0 reference block of the current block and a predetermined offset, and the L1 block is determined based on a position of a L1 reference block of the current block and the predetermined offset.
4. The method of claim 3 , wherein the offset includes at least one of a non-directional offset or a directional offset, and
wherein the directional offset includes an offset for at least one direction of left, right, top, bottom, top-left, top-right, bottom-left or bottom-right.
5. A method of encoding an image, comprising:
determining initial motion information of a current block based on a merge candidate list including a plurality of merge candidates;
determining delta motion information of the current block based on a sum of absolute difference (SAD) list for a search area, the SAD list including a plurality of SAD candidates;
updating the initial motion information of the current block based on the delta motion information; and
performing inter prediction on the current block based on the updated initial motion information,
wherein deriving the delta motion information is performed based on a comparison result between a reference SAD candidate and a predetermined threshold,
wherein the reference SAD candidate is representative of a SAD candidate corresponding to a non-directional offset, and
wherein when the reference SAD candidate is greater than or equal to the predetermined threshold, deriving the delta motion information comprises:
identifying a SAD candidate having a minimum value among the SAD candidates belonging to the SAD list; and
determining the delta motion information based on an offset corresponding to the identified SAD candidate.
6. A method of transmitting a bitstream, comprising:
determining initial motion information of a current block based on a merge candidate list including a plurality of merge candidates;
determining delta motion information of the current block based on a sum of absolute difference (SAD) list for a search area, the SAD list including a plurality of SAD candidates;
updating the initial motion information of the current block based on the delta motion information;
generating a prediction block of the current block by performing inter prediction on the current block based on the updated initial motion information;
generating a residual block of the current block based on the prediction block;
encoding the residual block to generate the bitstream; and
transmitting the bitstream,
wherein deriving the delta motion information is performed based on a comparison result between a reference SAD candidate and a predetermined threshold,
wherein the reference SAD candidate is representative of a SAD candidate corresponding to a non-directional offset, and
wherein when the reference SAD candidate is greater than or equal to the predetermined threshold, deriving the delta motion information comprises:
identifying a SAD candidate having a minimum value among the SAD candidates belonging to the SAD list; and
determining the delta motion information based on an offset corresponding to the identified SAD candidate.