Intra prediction mode encoding/decoding method and device, and recording medium in which bitstream is stored

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

deriving an intra prediction mode of a current block based on a most probable mode (MPM) list including five intra prediction modes;

deriving a reference sample for the current block based on the intra prediction mode; and

predicting the current block based on the intra prediction mode and the reference sample,

wherein the MPM list is configured to include a first intra prediction mode being equal to a left intra prediction mode, a second intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode+61)%64), a third intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode −1)%64), a fourth intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode+60)%64), and a fifth intra prediction mode which index is (2+intra prediction mode value of the left intra prediction mode %64)),

wherein an index of a left intra prediction mode is equal to an index of an upper intra prediction mode and greater than 1,

wherein the left intra prediction mode is an intra prediction mode of a block adjacent to a left side of the current block and the upper intra prediction mode is an intra prediction mode of a block adjacent to an upper side of the current block, and

wherein the current block is obtained by dividing a current picture including the current block using a quad-tree division method.

2. The method according to claim 1 , wherein in a case where a size of the current block is W×H, the block adjacent to the upper side of the current block is a block to which a [W−1, −1] sample belongs.

3. The method according to claim 1 , wherein in a case where a size of the current block is W×H, a block adjacent to a left side of the current block is a block to which a [−1, H−1] sample belongs.

4. The method according to claim 1 , wherein in a case where the intra prediction mode of the current block is a directional intra prediction mode and where a reference sample corresponding to the intra prediction mode is present at an integer position, reference sample filtering is performed without applying an interpolation filter to the reference sample.

5. A method of encoding an image, the method comprising:

determining an intra prediction mode of a current block;

deriving a reference sample for the current block based on the intra prediction mode;

predicting the current block based on the reference sample; and

encoding an intra prediction mode of the current block, wherein the intra prediction mode is encoded based on a most probable mode (MPM) list including five intra prediction modes,

wherein the MPM list is configured to include a first intra prediction mode being equal to a left intra prediction mode, a second intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode+61)%64), a third intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode −1)%64), a fourth intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode+60)%64), and a fifth intra prediction mode which index is (2+intra prediction mode value of the left intra prediction mode %64)),

wherein an index of a left intra prediction mode is equal to an index of an upper intra prediction mode and greater than 1,

wherein the left intra prediction mode is an intra prediction mode of a block adjacent to a left side of the current block and the upper intra prediction mode is an intra prediction mode of a block adjacent to an upper side of the current block, and

wherein the current block is obtained by dividing a current picture including the current block using a quad-tree division method.

6. The method according to claim 5 , wherein in a case where a size of the current block is W×H, the block adjacent to the upper side of the current block is a block to which a [W−1, −1] sample belongs.

7. The method according to claim 5 , wherein in a case where a size of the current block is W×H, a block adjacent to a left side of the current block is a block to which a [−1, H−1] sample belongs.

8. A method of transmitting a bitstream generated by an encoding method, the encoding method comprising:

determining an intra prediction mode of a current block;

deriving a reference sample for the current block based on the intra prediction mode;

predicting the current block based on the reference sample; and

encoding an intra prediction mode of the current block, wherein the intra prediction mode is encoded based on a most probable mode (MPM) list including five intra prediction modes,

wherein the MPM list is configured to include a first intra prediction mode being equal to a left intra prediction mode, a second intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode+61)%64), a third intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode −1)%64), a fourth intra prediction mode which index is (2+(intra prediction mode value of the left intra prediction mode+60)%64), and a fifth intra prediction mode which index is (2+intra prediction mode value of the left intra prediction mode %64)),

wherein an index of a left intra prediction mode is equal to an index of an upper intra prediction mode and greater than 1,

wherein the left intra prediction mode is an intra prediction mode of a block adjacent to a left side of the current block and the upper intra prediction mode is an intra prediction mode of a block adjacent to an upper side of the current block, and

wherein the current block is obtained by dividing a current picture including the current block using a quad-tree division method.