Method for encoding/decoding image and device thereof

1. A method of decoding a video, the method comprising:

determining at least one first block for partitioning a current frame which is one of at least one frame included in the video;

determining a first prediction mode indicating an intra-prediction method to be performed on a current first block which is one of the at least one first block, based on first intra-prediction mode information obtained from a bitstream, when intra-prediction is performed on the current first block;

determining a plurality of second blocks included in the current first block;

determining a reference direction to be used for a current second block which is one of the plurality of second blocks, based on a prediction direction determined according to the first intra-prediction mode information;

determining a plurality of prediction direction candidates to be used for the current second block, the plurality of prediction direction candidates including the reference direction;

determining second prediction modes indicating intra-prediction methods to be performed on the current second blocks, based on second intra-prediction mode information indicating one of the plurality of the prediction direction candidates, wherein the second intra prediction mode information is obtained from the bitstream with respect to each of the plurality of second blocks; and

decoding the video by performing intra-prediction based on the first prediction mode and the second prediction mode,

wherein the plurality of prediction direction candidates are determined by adding or subtracting a predetermined set of numbers to an index indicating the reference direction.

2. The method of claim 1 , wherein the determining of the second prediction modes comprises:

obtaining the second intra-prediction mode information from the bitstream related to a previous second block which is one of the plurality of second blocks; and

determining the second prediction mode of the current second block, based on the second intra-prediction mode information related to the previous second block and the first intra-prediction mode information.

3. The method of claim 2 , wherein the determining of the second prediction modes comprises:

determining the reference direction to be used for the current second block, based on a prediction direction determined according to the second intra-prediction mode information related to the previous second block.

4. The method of claim 1 , wherein, when the current second block is a last block among the plurality of second blocks, the determining of the second prediction modes comprises determining a prediction mode using the reference direction to be the second prediction mode of the current second block.

5. The method of claim 1 , wherein differences between indexes of the prediction direction candidates to be used for the current second block are uniform.

6. The method of claim 1 , wherein differences between indexes of the prediction direction candidates to be used for the current second block are not uniform.

7. The method of claim 1 , wherein the determining of the first prediction mode comprises determining an intra-prediction mode of the current first block, based on first intra-prediction mode information obtained from the bitstream related to a first neighboring block adjacent to the current first block.

8. The method of claim 1 , wherein the determining of the first prediction mode comprises determining the first prediction mode, based on the first intra-prediction mode information obtained from the bitstream related to the current first block.

9. The method of claim 1 , wherein the determining of the second prediction mode comprises:

obtaining a flag indicating whether intra-prediction is to be performed based on the first prediction mode and the second prediction modes from the bitstream;

and

when the flag indicates that intra-prediction is to be performed based on the first prediction mode and the second prediction modes, determining the second prediction mode by obtaining the second intra-prediction mode information from the bitstream with respect to each of the plurality of second blocks.

10. The method of claim 1 , wherein, when the first prediction mode indicates a directional intra-prediction mode, the determining of the second prediction modes comprises determining second prediction modes of second blocks in the same row or column among the plurality of second blocks to be the same, based on a direction of intra-prediction related to the first prediction mode.

11. The method of claim 1 , wherein the determining of the plurality of second blocks comprises determining a plurality of non-square second blocks included in the first block.

12. The method of claim 1 , wherein the first block comprises a coding unit, and

the plurality of second blocks comprise transformation units.

13. A non-transitory computer-readable recording medium having recorded thereon a computer program for executing the method of claim 1 .

14. An apparatus for decoding a video, the apparatus comprising:

one or more processors,

a bitstream obtainer configured to obtain first intra-prediction mode information and second intra-prediction mode information from a bitstream; and

a decoder configured to determine at least one first block for partitioning a current frame which is one of at least one frame included in the video, determine whether intra-prediction is to be performed on a current first block which is one of the at least one first block, determine a first prediction mode indicating an intra-prediction method to be performed on the current first block based on the first intra-prediction mode information when intra-prediction is to be performed on the current first block, determine a plurality of second blocks included in the current first block, determine a reference direction to be used for a current second block which is one of the plurality of second blocks, based on a prediction direction determined according to the first intra-prediction mode information, determine a plurality of prediction direction candidates to be used for the current second block, the plurality of prediction direction candidates including the reference direction, determine second prediction mode indicating intra-prediction methods to be performed on the current second block based on the second intra-prediction mode information indicating one of the plurality of the prediction direction candidates, wherein the second intra prediction mode information is obtained with respect to each of the plurality of second blocks, and decode the video by performing intra-prediction based on the first prediction mode and the second prediction modes,

wherein the plurality of prediction direction candidates are determined by adding or subtracting a predetermined set of numbers to an index indicating the reference direction and

wherein the bitstream obtainer and the decoder are executed in said one or more processors.

15. A method of encoding a video, the method comprising:

determining at least one first block for partitioning a current frame which is one of at least one frame included in the video;

determining whether intra-prediction is to be performed on a current first block which is one of the at least one first block;

when intra-prediction is to be performed on the current first block, determining a first prediction mode indicating an intra-prediction method to be performed on the current first block;

determining a plurality of second blocks included in the current first block;

determining a reference direction to be used for a current second block which is one of the plurality of second blocks, based on a prediction direction determined according to the first prediction mode;

determining a plurality of prediction direction candidates to be used for the current second block, the plurality of prediction direction candidates including the reference direction;

determining second prediction modes indicating intra-prediction methods to be performed on the current second blocks, based on one of the plurality of the prediction direction candidates;

encoding the video by performing intra-prediction based on the first prediction mode and the second prediction modes; and

generating a bitstream including data regarding the encoded video, first intra-prediction mode information indicating a current first prediction mode, and second intra-prediction mode information indicating the second prediction modes,

wherein the plurality of prediction direction candidates are determined by adding or subtracting a predetermined set of numbers to an index indicating the reference direction.