Method for encoding/decoding motion vector and apparatus thereof
A method for encoding/decoding a motion vector and an apparatus thereof are disclosed. The method includes defining a candidate motion vector set with respect to a current motion vector; selecting a predicted motion vector from the candidate motion vector set; determining a predictability of the predicted motion vector in a decoding apparatus; encoding the current motion vector by using a motion vector prediction mode for indicating the predicted motion vector and the predictability, if the predictability is determined positive; and encoding the current motion vector by using a motion vector prediction mode for indicating a default predicted motion vector and an unpredictability, if the predictability is determined negative. According to the disclosure, it becomes unnecessary to directly notify of the predicted motion vector of the current motion vector to the decoding apparatus, and instead a predetermined shared function is provided to inform of or search the predicted motion vector.
1. A method for decoding a current motion vector of a current block, which is located in a current picture, at an apparatus for decoding an encoded video, the method comprising:
extracting, from a bitstream, mode information for use in selecting a motion vector prediction mode among a plurality of motion vector prediction modes, wherein the plurality of motion vector prediction modes are different from each other and indicate different ways to determine the current motion vector of the current block; and
when the mode information indicates a first motion vector prediction mode among the plurality of motion vector prediction modes, performing a process comprising:
decoding the bitstream to produce a differential vector of the current block;
deriving a set of candidate motion vectors from motion vectors of a plurality of neighboring blocks of the current block,
wherein the set of candidate motion vectors is used for determining a prediction motion vector of the current block, not determining the current motion vector itself of the current block, to be added to the produced differential vector,
wherein the plurality of neighboring blocks include at least one block spatially adjacent to the current block in the current picture and at least one block in a reference picture other than the current picture, wherein a position of said at least one block in the reference picture is derived based on a position of the current block in the current picture;
selecting a candidate motion vector from among the set of the candidate motion vectors;
determining a prediction motion vector of the current block as the selected candidate motion vector, wherein the selected candidate motion vector has been derived from said at least one block spatially adjacent block or said at least one block in a reference picture; and
reconstructing the current motion vector of the current block by adding the produced differential vector to the prediction motion vector of the current block,
wherein the at least one block spatially adjacent to the current block includes one or more of blocks located at left, upper, upper right and upper left sides of the current block.
2. The method of claim 1 , wherein the position of the at least one block in the reference picture is identical to the position of the current block in the current picture.
3. The method of claim 1 , wherein the selecting comprises:
selecting the candidate motion vector based on information included in the bitstream.
4. The method of claim 1 , further comprising:
reconstructing the current motion vector of the current block by using a predefined motion vector, when the motion information indicates a second motion vector prediction mode.
5. An apparatus for decoding a current motion vector of a current block, which is located in a current picture, to decode an encoded video, the apparatus comprising:
a mode information decoder configured to extract, from a bitstream, mode information for use in selecting a motion vector prediction mode among a plurality of motion vector prediction modes, wherein the plurality of motion vector prediction modes are different from each other and indicate different ways to determine the current motion vector of the current block;
a prediction mode determiner configured to determine whether the extracted mode information indicates a first motion vector prediction mode among the plurality of motion vector prediction modes; and
a prediction motion vector determiner configured to, in response to the extracted mode information being indicative of the first motion vector prediction mode,
derive a set of candidate motion vectors from motion vectors of a plurality of neighboring blocks of the current block,
wherein the set of candidate motion vectors is used for determining a prediction motion vector of the current block, not determining the current motion vector itself of the current block, to be added to a differential vector,
wherein the plurality of neighboring blocks include at least one block spatially adjacent to the current block in the current picture and at least one block in a reference picture other than the current picture, wherein a position of said at least one block in the reference picture is derived based on a position of the current block in the current picture;
select a candidate motion vector from among the set of the candidate motion vectors; and
determine a prediction motion vector of the current block as the selected candidate motion vector, wherein the selected candidate motion vector has been derived from said at least one block spatially adjacent block or said at least one block in a reference picture; and
a reconstructor configured to reconstruct the current motion vector of the current block by adding the prediction motion vector of the current block to the differential vector produced by decoding the bitstream,
wherein the at least one block spatially adjacent to the current block includes one or more of blocks located at left, upper, upper right and upper left sides of the current block.
6. The apparatus of claim 5 , wherein the position of the at least one block in the reference picture is identical to the position of the current block in the current picture.
7. The apparatus of claim 5 , wherein the prediction motion vector determiner is configured to select the candidate motion vector from the set of candidate motion vectors, based on information included in the bitstream.
8. The apparatus of claim 5 , wherein the reconstructor is configured to reconstruct the current motion vector of the current block by using a predefined motion vector, when the motion information indicates a second motion vector prediction mode.
9. The method of claim 1 , wherein the deriving the set of candidate motion vectors comprises:
excluding one of two candidate motion vectors included in the set when the two candidate motion vectors have the same value.
10. The apparatus of claim 5 , wherein the prediction motion vector determiner is configured to compare a first element and a second element included in the set and exclude one of the first element and the second element from the set when the first element and the second element have the same value.