Image encoding/decoding method and device
The image encoding/decoding method and device according to the present invention can construct a merge candidate list of a current block, derive motion information of the current block on the basis of the merge candidate list and a merge index of the current block, derive a motion vector difference of the current block, correct a motion vector of the current block by means of the motion vector difference, and carry out motion compensation on the current block by means of the corrected motion vector.
1. An image decoding method, comprising:
configuring a merge candidate list of a current block;
deriving motion information of the current block based on a merge index of the current block and the merge candidate list, the motion information including at least one of a motion vector or a reference picture index;
deriving a motion vector difference value of the current block;
modifying the motion vector of the current block by using the motion vector difference value; and
performing motion compensation of the current block by using the modified motion vector,
wherein deriving the motion vector difference value comprises:
obtaining, from a bitstream, a first index specifying a length candidate among a plurality of length candidates and a second index specifying a direction candidate among a plurality of direction candidates,
wherein the motion vector difference value is derived based on a merge offset vector,
wherein the merge offset vector is determined based on the length candidate specified by the first index and the direction candidate specified by the second index, and
wherein a range of the length candidates is determined differently according to a precision of the motion vector of the current block.
2. The method of claim 1 , wherein the merge candidate list includes at least one of a spatial merge candidate or a temporal merge candidate of the current block,
wherein motion information of a previous block belonging to a motion information list of the current block is added to the merge candidate list, and
wherein the previous block is one or more blocks which are decoded before the current block.
3. The method of claim 1 , wherein deriving the motion vector difference value is selectively performed based on a flag obtained from the bitstream, and
wherein the flag represents whether the motion vector difference value is used in a merge mode.
4. The method of claim 3 , wherein a maximum number of merge candidates available for the current block is adaptively determined according to a value of the flag.
5. The method of claim 4 , wherein the motion vector difference value is derived by applying a predetermined scaling factor to the merge offset vector, and
wherein the scaling factor is determined based on a POC difference between a current picture to which the current block belongs and a reference picture of the current block.
6. The method of claim 1 ,
wherein the direction candidates include a left, right, top and bottom direction.
7. An image encoding method, comprising:
configuring a merge candidate list of a current block;
determining motion information of the current block based on the merge candidate list, wherein the motion information includes at least one of a motion vector or a reference picture index, and wherein a merge index for specifying the motion information of the current block is encoded into a bitstream;
determining a motion vector difference value of the current block;
modifying the motion vector of the current block by using the motion vector difference value; and
performing motion compensation of the current block by using the modified motion vector,
wherein a first index specifying a length candidate among a plurality of length candidates and a second index specifying a direction candidate among a plurality of direction candidates are encoded into the bitstream,
wherein the motion vector difference value is determined based on a merge offset vector,
wherein the merge offset vector is determined based on the length candidate and the direction candidate, and
wherein a range of the length candidates is determined differently according to a precision of the motion vector of the current block.
8. A non-transitory computer-readable medium for storing a bitstream generated by an image encoding method, the image encoding method comprising:
configuring a merge candidate list of a current block;
determining motion information of the current block based on the merge candidate list, wherein the motion information includes at least one of a motion vector or a reference picture index, and wherein a merge index for specifying the motion information of the current block is encoded into the bitstream;
determining a motion vector difference value of the current block;
modifying the motion vector of the current block by using the motion vector difference value; and
performing motion compensation of the current block by using the modified motion vector,
wherein a first index specifying a length candidate among a plurality of length candidates and a second index specifying a direction candidate among a plurality of direction candidates are encoded into the bitstream,
wherein the motion vector difference value is determined based on a merge offset vector,
wherein the merge offset vector is determined based on the length candidate and the direction candidate, and
wherein a range of the length candidates is determined differently according to a precision of the motion vector of the current block.