Intra prediction method and apparatus in image coding system
An image decoding method performed by a decoding apparatus according to the present disclosure comprises the steps of: obtaining a reference sample line index of a current block and most probable mode (MPM)-related information; constructing an alternative MPM list on the basis of the reference sample line index; deriving an intra prediction mode of the current block on the basis of the alternative MPM list and the MPM-related information; and generating a predicted block of the current block on the basis of the intra prediction mode, wherein the alternative MPM list is constructed on the basis of an intra prediction mode of an upper adjacent block of the current block and an intra prediction mode of a left adjacent block of the current block.
1. An image decoding method performed by a decoding apparatus, the method comprising:
obtaining image information including prediction related information, information on a reference sample line index and most probable mode (MPM) related information of a current block through a bitstream;
determining that an intra prediction is applied for the current block based on the prediction related information;
configuring an MPM list for the current block;
deriving an intra prediction mode of the current block based on the MPM list and the MPM related information;
deriving reference neighboring samples based on the information on the reference sample line index;
generating a predicted block for the current block based on the intra prediction mode and the reference neighboring samples; and
generating a reconstructed picture based on the predicted block,
wherein the MPM list is configured based on a first intra prediction mode of a left neighboring block of the current block and a second intra prediction mode of a top neighboring block of the current block,
wherein the MPM list comprise a first MPM candidate, a second MPM candidate, a third MPM candidate, a fourth MPM candidate and a fifth MPM candidate,
wherein based on a case that a mode value of the first intra prediction mode is equal to a mode value of the second intra prediction mode and the mode value of the first intra prediction mode is greater than a mode value of a DC mode,
a mode value of the first MPM candidate is equal to the mode value of the first intra prediction mode,
a mode value of the second MPM candidate is equal to a result of an equation of (L+61)%64+2, L being the mode value of the first intra prediction mode,
a mode value of the third MPM candidate is equal to a result of an equation of (L−1)%64+2,
a mode value of the fourth MPM candidate is equal to a result of an equation of (L+60)%64+2, and
a mode value of the fifth MPM candidate is equal to a result of an equation of (L)%64+2.
2. The image decoding method of claim 1 , wherein the MPM related information comprises an MPM flag information related to whether the intra prediction mode of the current block is one of MPM candidates and an MPM index information indicating the intra prediction mode of the current block in the MPM list.
3. The image decoding method of claim 2 , wherein the intra prediction mode of the current block is derived based on the MPM list and the MPM index information in case that a value of the MPM flag is 1.
4. The image decoding method of claim 2 , wherein the intra prediction mode of the current block is derived based on remaining intra prediction modes excluding the MPM candidates among all available intra prediction modes in case that a value of the MPM flag is 0.
5. An image encoding method performed by an encoding apparatus, the method comprising:
determining that an intra prediction is applied for a current block;
generating prediction related information;
deriving a reference sample line index of the current block;
generating information on the reference sample line index;
configuring a most probable mode (MPM) list for the current block;
deriving an intra prediction mode of the current block based on the MPM list;
generating MPM related information of the current block; and
generating a bitstream by encoding image information including the prediction related information, the information on the reference sample line index and the MPM related information,
wherein the MPM list is configured based on a first intra prediction mode of a left neighboring block of the current block and a second intra prediction mode of a top neighboring block of the current block,
wherein the MPM list comprise a first MPM candidate, a second MPM candidate, a third MPM candidate, a fourth MPM candidate and a fifth MPM candidate,
wherein based on a case that a mode value of the first intra prediction mode is equal to a mode value of the second intra prediction mode and the mode value of the first intra prediction mode is greater than a mode value of a DC mode,
a mode value of the first MPM candidate is equal to the mode value of the first intra prediction mode,
a mode value of the second MPM candidate is equal to a result of an equation of (L+61)%64+2, L being the mode value of the first intra prediction mode,
a mode value of the third MPM candidate is equal to a result of an equation of (L−1)%64+2,
a mode value of the fourth MPM candidate is equal to a result of an equation of (L+60)%64+2, and
a mode value of the fifth MPM candidate is equal to a result of an equation of (L)%64+2.
6. The image encoding method of claim 5 , wherein the MPM related information comprises an MPM flag information related to whether the intra prediction mode of the current block is one of MPM candidates and an MPM index information indicating the intra prediction mode of the current block in the MPM list.
7. A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising:
determining that an intra prediction is applied for a current block;
generating prediction related information;
deriving a reference sample line index of a current block;
generating information on the reference sample line index;
configuring a most probable mode (MPM) list for the current block;
deriving an intra prediction mode of the current block based on the MPM list;
generating MPM related information of the current block; and
generating the bitstream by encoding image information including the prediction related information, the information on the reference sample line index and the MPM related information,
wherein the MPM list is configured based on a first intra prediction mode of a left neighboring block of the current block and a second intra prediction mode of a top neighboring block of the current block,
wherein the MPM list comprise a first MPM candidate, a second MPM candidate, a third MPM candidate, a fourth MPM candidate and a fifth MPM candidate,
wherein based on a case that a mode value of the first intra prediction mode is equal to a mode value of the second intra prediction mode and the mode value of the first intra prediction mode is greater than a mode value of a DC mode,
a mode value of the first MPM candidate is equal to the mode value of the first intra prediction mode,
a mode value of the second MPM candidate is equal to a result of an equation of (L+61)%64+2, L being the mode value of the first intra prediction mode,
a mode value of the third MPM candidate is equal to a result of an equation of (L−1)%64+2,
a mode value of the fourth MPM candidate is equal to a result of an equation of (L+60)%64+2, and
a mode value of the fifth MPM candidate is equal to a result of an equation of (L)%64+2.