Method and apparatus for encoding a motion vector, and method and apparatus for encoding/decoding image using same

1. An apparatus for reconstructing a current motion vector of a current block in a current frame by determining a predicted motion vector of the current motion vector, the apparatus comprising:

a decoder configured to reconstruct a differential motion vector and a prediction candidate identification flag by decoding a bitstream; and

a motion vector reconstructor configured to

derive one or more motion vector prediction candidates to determine the predicted motion vector of the current motion vector,

set the predicted motion vector to a motion vector prediction candidate identified by the prediction candidate identification flag among the one or more motion vector prediction candidates, and

reconstruct the current motion vector of the current block by adding the predicted motion vector to the differential motion vector,

wherein the motion vector reconstructor comprises

means for deriving one or more first motion vector prediction candidates from motion vectors of one or more adjacent blocks of the current block in the current frame, and

means for deriving a second motion vector prediction candidate from a motion vector of a block in a reference frame decoded before the current frame, wherein a position of the block in the reference frame is derived based on a position of the current block in the current frame,

wherein the motion vector reconstructor is configured to select one of the first motion vector prediction candidates from upper blocks adjacent to the current block, and one of the first motion vector prediction candidates from left blocks adjacent to the current block,

wherein the motion vector reconstructor is configured to derive the second motion vector prediction candidate from the motion vector of the block in the reference frame which is at a same position with or at a lower right side of the current block in the current frame, and

wherein the motion vector reconstructor is configured to derive the one or more motion vector prediction candidates from among the first motion vector prediction candidates and the second motion vector prediction candidate,

wherein the upper blocks include adjacent blocks located at an upper left side, an upper side or an upper right side of the current block.

2. The apparatus of claim 1 , wherein the motion vector reconstructor is configured to select only one motion vector prediction candidate among two of motion vector prediction candidates which are within a preset distance.

3. The apparatus of claim 1 , wherein the decoder is configured to decode a prediction candidate selection flag from the bitstream,

wherein the motion vector reconstructor is configured to derive the one or more motion vector prediction candidates based on the prediction candidate selection flag.

4. The apparatus of claim 1 , wherein the motion vector reconstructor is configured to independently determine each of an x-component and a y-component of the predicted motion vector by

setting an x-component of the predicted motion vector to an x-component of one motion vector prediction candidate among the one or more motion vector prediction candidates and

setting a y-component of the predicted motion vector to a y-component of one motion vector prediction candidate among the one or more motion vector prediction candidates.

5. A method for reconstructing a current motion vector of a current block in a current frame by determining a predicted motion vector of the current motion vector, the method comprising:

reconstructing a differential motion vector and a prediction candidate identification flag by decoding a bitstream;

deriving one or more motion vector prediction candidates to determine the predicted motion vector of the current motion vector,

setting the predicted motion vector to a motion vector prediction candidate identified by the prediction candidate identification flag among the one or more motion vector prediction candidates, and

reconstructing the current motion vector of the current block by adding the predicted motion vector to the differential motion vector,

wherein the derivation of the one or more motion vector prediction candidates comprises:

deriving one or more of first motion vector prediction candidates from motion vectors of one or more adjacent blocks of the current block in the current frame; and

deriving a second motion vector prediction candidate from a motion vector of a block in a reference frame decoded before the current frame, wherein a position of the block in the reference frame is derived based on a position of the current block in the current frame,

wherein the deriving of the one or more of first motion vector prediction candidates comprises:

selecting one of the first motion vector prediction candidates from left blocks adjacent to the current block, and

selecting one of the first motion vector prediction candidates from upper blocks adjacent to the current block,

wherein the second motion vector prediction candidate is derived from the motion vector of the block in the reference frame which is at a same position with or at a lower right side of the current block in the current frame, and

wherein the one or more motion vector prediction candidates are derive from among the first motion vector prediction candidates and the second motion vector prediction candidate,

wherein the upper blocks include adjacent blocks located at an upper left side, an upper side or an upper right side of the current block.

6. The method of claim 5 , wherein the derivation of one or more motion vector prediction candidates comprising

selecting only one motion vector prediction candidate among two of motion vector prediction candidates which are within a preset distance.

7. The method of claim 5 , further comprising decoding a prediction candidate selection flag from the bitstream,

wherein the one or more motion vector prediction candidates are derived based on the prediction candidate selection flag.

8. The method of claim 5 , wherein the predicted motion vector is set independently for each of an x-component and a y-component of the predicted motion vector by

setting an x-component of the predicted motion vector to an x-component of one motion vector prediction candidate among the one or more motion vector prediction candidates and

setting a y-component of the predicted motion vector to a y-component of one motion vector prediction candidate among the one or more motion vector prediction candidates.