Encoding and decoding images using inter-prediction

1. A method for decoding an image, the method comprising:

receiving mode information on inter prediction of a current block including first information indicating whether there is not a residual signal for the current block and merge flag information indicating whether a prediction mode for the current block is a merge mode, wherein the first information is signaled prior to the merge flag information;

decoding the received mode information;

generating a prediction block by performing inter prediction on the current block on the basis of the decoded mode information; and

generating a reconstructed block by using the generated prediction block, wherein the mode information further includes a merge index indicating a block used for deriving motion information of the current block when the merge flag information indicates that the prediction mode for the current block is the merge mode,

wherein the step of performing inter prediction comprises:

constituting candidate blocks for the inter prediction of the current block,

wherein the candidate blocks comprises four spatial neighboring blocks, (i) the bottom-most block among neighboring blocks adjacent to the left edge of the current block, (ii) the right-most block among neighboring blocks adjacent to the top edge of the current block, (iii) the right top corner block adjacent to the current block, and (iv) the left bottom corner block adjacent to the current block, when the bottom-most block, the right-most block, the right top corner block, and the left bottom corner block are available; and

setting motion information of the current block equal to motion vector of the block indicated by the merge index among the candidate blocks.

2. The method of claim 1 , wherein the first information is decoded prior to the merge flag information.

3. The method of claim 1 , wherein the derived motion information is one of L 0 motion information, L 1 motion information, and Bi motion information.

4. The method of claim 1 , wherein, if there is no residual signal for the current block, a residual value for a luma component and a residual value for a chroma component are derived as 0.

5. The method of claim 1 , wherein the candidate blocks haves the same configuration when there is a residual signal for the current block and when the prediction mode for the current block is the merge mode.

6. The method of claim 1 , wherein the maximum number of the candidate blocks is five.

7. The method of claim 1 , wherein the first information comprises skip flag information indicating whether there is not a residual signal for the current block, the method further comprising:

decoding a merge index identifying a block which is used for deriving a motion information of the current block from the candidate blocks when the skip flag information is 1.

8. The method of claim 1 , wherein the first information comprises skip flag information indicating whether there is not a residual signal for the current block, the method further comprising;

decoding the merge flag information when the skip flag information is 0; and

decoding a merge index identifying a block which is used for deriving a motion information of the current block from the candidate blocks when the merge flag information indicates that the prediction mode for the current block is the merge mode.

9. The method of claim 1 , wherein the four spatial neighboring blocks have priorities in the candidate blocks in an order of: the bottom-most block among neighboring blocks adjacent to the left edge of the current block, the right-most block among neighboring blocks adjacent to the top edge of the current block, the right top corner block adjacent to the current block, and the left bottom corner block adjacent to the current block.

10. The method of claim 6 , wherein the candidate blocks consist of four spatial neighboring blocks and one temporal neighboring block.