Method for processing image on basis of intra prediction mode, and device therefor
Disclosed are a method for decoding a video signal and a device therefore. More particularly, a method for decoding an image based on an intra prediction mode, may comprise the steps of: acquiring a most probable mode (MPM) flag for indicating whether an MPM is applied to a current block, the MPM representing a mode in which an intra prediction mode of the current block is induced from an intra predicted block neighboring the current block; configuring an MPM list, on the basis of whether intra prediction modes of a left neighboring block and an above neighboring block of the current block satisfy predefined conditions, if the MPM is applied to the current block; acquiring an MPM index for indicating, within the MPM list, a specific intra prediction mode; and generating a prediction block for the current block by using the intra prediction mode specified by the MPM index.
1. A method of decoding an image based on an intra prediction mode by an apparatus, the method comprising:
obtaining a most probable mode (MPM) flag informing whether an MPM is applied to a current block, the MPM denoting a mode in which an intra prediction mode of the current block is derived from an intra-predicted block around the current block;
configuring an MPM list based on whether intra prediction modes of left and upper neighboring blocks of the current block meet a predefined condition;
obtaining an MPM index indicating a specific intra prediction mode in the MPM list; and
generating a prediction block of the current block based on an intra prediction mode specified by the MPM index,
wherein the configuring the MPM list includes: deriving a first MPM list based on that the intra prediction mode of the left neighboring block and the intra prediction mode of the upper neighboring block are non-angular modes, and
wherein the first MPM list comprises a horizontal intra prediction mode a value of which is 18, a vertical intra prediction mode a value of which is 50, an intra prediction mode having a value of 46 obtained by subtracting 4 from the value of the vertical intra prediction mode, and an intra prediction mode having a value of 54 obtained by adding 4 to the value of the vertical intra prediction mode.
2. The method of claim 1 , wherein the left neighboring block is set as a block including a pixel horizontally adjacent to a left lower sample in the current block, and
wherein the upper neighboring block is set as a block including a pixel vertically adjacent to an upper right sample in the current block.
3. The method of claim 1 , wherein the configuring the MPM list includes configuring one of a specific number of MPM lists based on four pre-defined conditions.
4. The method of claim 3 , wherein the configuring the MPM list includes:
configuring a first MPM list based on that a first condition is met;
configuring a second MPM list based on that a second condition and a third condition are met but the first condition is not met;
configuring a third MPM list based on that the second condition and a fourth condition are met but the first condition and the third condition are not met;
configuring a fourth MPM list based on that the second condition is met but the first condition, the third condition, and the fourth condition are not met; and
configuring a fifth MPM list based on that the first condition and the second condition are not met.
5. The method of claim 4 , wherein the first condition is set as whether the intra prediction modes of the left neighboring block and the upper neighboring block are smaller than, or equal to, a DC mode,
wherein the second condition is set as whether the intra prediction modes of the left neighboring block and the upper neighboring block are not equal to each other,
wherein the third condition is set as whether the intra prediction mode of the left neighboring block or the intra prediction mode of the upper neighboring block is smaller than or equal to the DC mode, and
wherein the fourth condition is set as whether a difference between a maximum mode indicating a mode with a larger mode index value among the intra prediction modes of the left neighboring block and the upper neighboring block and a minimum mode indicating a mode with a smaller mode index value among the intra prediction modes of the left neighboring block and the upper neighboring block is smaller than a predefined value.
6. A method of encoding an image based on an intra prediction mode by an apparatus, the method comprising:
signaling a most probable mode (MPM) flag informing whether an MPM is applied to a current block, the MPM denoting a mode in which an intra prediction mode of the current block is derived from an intra-predicted block around the current block;
configuring an MPM list based on whether intra prediction modes of left and upper neighboring blocks of the current block meet a predefined condition;
signaling an MPM index indicating a specific intra prediction mode in the MPM list; and
generating a prediction block of the current block based on an intra prediction mode specified by the MPM index,
wherein the configuring the MPM list includes: deriving a first MPM list based on that the intra prediction mode of the left neighboring block and the intra prediction mode of the upper neighboring block are non-angular modes, and
wherein the first MPM list comprises a horizontal intra prediction mode a value of which is 18, a vertical intra prediction mode a value of which is 50, an intra prediction mode having a value of 46 obtained by subtracting 4 from the value of the vertical intra prediction mode, and an intra prediction mode having a value of 54 obtained by adding 4 to the value of the vertical intra prediction mode.
7. The method of claim 6 , wherein the left neighboring block is set as a block including a pixel horizontally adjacent to a left lower sample in the current block, and
wherein the upper neighboring block is set as a block including a pixel vertically adjacent to an upper right sample in the current block.
8. The method of claim 6 , wherein the configuring the MPM list includes configuring one of a specific number of MPM lists based on four pre-defined conditions.
9. The method of claim 8 , wherein the configuring the MPM list includes:
configuring a first MPM list based on that a first condition is met;
configuring a second MPM list based on that a second condition and a third condition are met but the first condition is not met;
configuring a third MPM list based on that the second condition and a fourth condition are met but the first condition and the third condition are not met;
configuring a fourth MPM list based on that the second condition is met but the first condition, the third condition, and the fourth condition are not met; and
configuring a fifth MPM list based on that the first condition and the second condition are not met.
10. The method of claim 9 , wherein the first condition is set as whether the intra prediction modes of the left neighboring block and the upper neighboring block are smaller than, or equal to, a DC mode,
wherein the second condition is set as whether the intra prediction modes of the left neighboring block and the upper neighboring block are not equal to each other,
wherein the third condition is set as whether the intra prediction mode of the left neighboring block or the intra prediction mode of the upper neighboring block is smaller than or equal to the DC mode, and
wherein the fourth condition is set as whether a difference between a maximum mode indicating a mode with a larger mode index value among the intra prediction modes of the left neighboring block and the upper neighboring block and a minimum mode indicating a mode with a smaller mode index value among the intra prediction modes of the left neighboring block and the upper neighboring block is smaller than a predefined value.
11. A non-transitory computer-readable medium for storing encoded image information generated by performing steps of:
signaling a most probable mode (MPM) flag informing whether an MPM is applied to a current block, the MPM denoting a mode in which an intra prediction mode of the current block is derived from an intra-predicted block around the current block;
configuring an MPM list based on whether intra prediction modes of left and upper neighboring blocks of the current block meet a predefined condition;
signaling an MPM index indicating a specific intra prediction mode in the MPM list; and
generating a prediction block of the current block based on an intra prediction mode specified by the MPM index,
wherein the configuring the MPM list includes: deriving a first MPM list based on that the intra prediction mode of the left neighboring block and the intra prediction mode of the upper neighboring block are non-angular modes, and
wherein the first MPM list comprises a horizontal intra prediction mode a value of which is 18, a vertical intra prediction mode a value of which is 50, an intra prediction mode having a value of 46 obtained by subtracting 4 from the value of the vertical intra prediction mode, and an intra prediction mode having a value of 54 obtained by adding 4 to the value of the vertical intra prediction mode.