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

1. An apparatus for decoding a current motion vector of a current block in a current frame from a bitstream by determining a predicted motion vector corresponding to the current motion vector of the current block, the apparatus comprising:

a differential motion vector decoder configured to reconstruct a differential motion vector by decoding an encoded differential motion vector included in the bitstream;

a motion vector reconstructor configured to:

select one or more motion vector prediction candidates to determine the predicted motion vector corresponding to the current motion vector,

determine the predicted motion vector 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, and

a prediction candidate identification flag decoder configured to reconstruct a prediction candidate identification flag by decoding an encoded prediction candidate identification flag,

wherein the motion vector reconstructor is configured to determine a motion vector prediction candidate identified by the prediction candidate identification flag among the one or more motion vector prediction candidates to be the predicted motion vector, and

wherein the motion vector reconstructor comprises:

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

means for selecting a second motion vector prediction candidate from a block in a reference frame other than 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.

2. The apparatus of claim 1 , wherein the motion vector reconstructor is configured to select the one or more of first motion vector prediction candidates from at least one of the adjacent blocks located at an upper left side, an upper side or an upper right side of the current block.

3. The apparatus of claim 1 , wherein the motion vector reconstructor is configured to select the second motion vector prediction candidate from the block in the reference frame which is at a same position with the current block or neighboring to the same position with the current block.

4. 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.

5. The apparatus of claim 1 , wherein the prediction candidate identification flag decoder is configured to decode a part of bits included in a bit-stream by the prediction candidate identification flag,

the motion vector reconstructor is configured to determine the motion vector prediction candidate identified as the predicted motion vector when the motion vector prediction candidate having the highest probability to be determined as the current motion vector is identified, and

the prediction candidate identification flag decoder is configured to decode additional bits included in the bit-stream when the motion vector prediction candidate having the highest probability to be determined as the current motion vector is not identified.

6. The apparatus of claim 1 , further comprising

a prediction candidate selection flag decoder configured to reconstruct a prediction candidate selection flag by decoding an encoded prediction candidate selection flag.

7. The apparatus of claim 6 , wherein the motion vector reconstructor is configured to determine a motion vector prediction candidate identified by the prediction candidate selection flag having been reconstructed, as the one or more motion vector prediction candidates.

8. The apparatus of claim 1 , wherein the motion vector reconstructor is configured to select the one or more motion vector prediction candidates either among the one or more of first motion vector prediction candidates or among the second motion vector prediction candidate.

9. The apparatus of claim 1 , 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.

10. A method performed by an apparatus for decoding a current motion vector of a current block in a current frame from a bitstream by determining a predicted motion vector corresponding to the current motion vector of the current block, the method comprising:

decoding an encoded differential motion vector included in the bitstream, to reconstruct a differential motion vector;

selecting one or more motion vector prediction candidates to determine the predicted motion vector corresponding to the current motion vector;

determining the predicted motion vector 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 selecting of the one or more motion vector prediction candidates comprises:

selecting one or more of first motion vector prediction candidates from one or more adjacent blocks of the current block in the current frame, and

selecting a second motion vector prediction candidate from a block in a reference frame other than 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, and

wherein the determining of the predicted motion vector comprising:

decoding an encoded prediction candidate identification flag to reconstruct a prediction candidate identification flag, and

determining a motion vector prediction candidate identified by the prediction candidate identification flag among the one or more motion vector prediction candidates to be the predicted motion vector.

11. The method of claim 10 , wherein the one or more of first motion vector prediction candidates are selected from at least one of the adjacent blocks located at an upper left side, an upper side or an upper right side of the current block.

12. The method of claim 10 , wherein the second motion vector prediction candidate is selected from the block in the reference frame which is at a same position with the current block or neighboring to the same position with the current block.

13. The method of claim 10 , wherein the selecting 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.

14. The method of claim 10 , wherein the selecting one or more of the first motion vector prediction candidates comprises:

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

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