Intra prediction-based image coding method using MPM list and apparatus therefor
An image decoding method according to the present disclosure comprises deriving a first candidate intra prediction mode based on a first neighboring block of a current block; deriving a second candidate intra prediction mode based on a second neighboring block of the current block; constructing MPM (Most Probable Mode) list of the current block based on the first candidate intra prediction mode and the second candidate intra prediction mode; deriving an intra prediction mode for the current block based on the MPM list; and generating a prediction sample for the current block based on the intra prediction mode, wherein the first neighboring block is a left neighboring block located at the lowermost side among neighboring blocks adjacent to a left boundary of the current block, and wherein the second neighboring block is an upper neighboring block located at the rightmost side among neighboring blocks adjacent to an upper boundary of the current block.
1. A decoding apparatus for image decoding, the decoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
obtain prediction information including an MPM index from a bitstream;
perform an intra prediction for the current block based on the prediction information to generate prediction samples; and
generate reconstructed samples for the current block based on the prediction samples for the current block,
wherein the at least one processor configured to perform the intra prediction for the current block comprises the at least one processor configured to:
derive a first candidate intra prediction mode based on a first neighboring block of the current block;
derive a second candidate intra prediction mode based on a second neighboring block of the current block;
construct an intra prediction mode candidate list of the current block based on the first candidate intra prediction mode and the second candidate intra prediction mode;
derive an intra prediction mode for the current block based on the intra prediction mode candidate list and the MPM index; and
generate the prediction samples for the current block based on the intra prediction mode,
wherein the first neighboring block is a left neighboring block located at the lowermost side among neighboring blocks adjacent to a left boundary of the current block,
wherein the second neighboring block is an upper neighboring block located at the rightmost side among neighboring blocks adjacent to an upper boundary of the current block,
wherein, based on a determination that a size of the current block is W×H, and x and y components of a top-left sample position of the current block are xN and yN respectively, the first neighboring block is a block including a sample at the coordinates of (xN−1, yN+H−1), and the second neighboring block is a block including a sample at the coordinates of (xN+W−1, yN−1), and
wherein the at least one processor configured to construct the intra prediction mode candidate list comprises the at least one processor configured to:
determine whether the first candidate intra prediction mode is equal to the second candidate intra prediction mode, and
determine whether a mode value of the first candidate intra prediction mode or a mode value of the second candidate intra prediction mode is greater than a mode value of a DC intra prediction mode.
2. An encoding apparatus for image encoding, the encoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
determine that an intra prediction is applied for a current block;
perform the intra prediction for the current block to generate prediction samples;
generate residual samples for the current block based on prediction samples for the current block; and
encode image information including prediction information including an MPM index related to the intra prediction to output a bitstream,
wherein the at least one processor configured to perform the intra prediction for the current block comprises the at least one processor configured to:
derive a first candidate intra prediction mode based on a first neighboring block of the current block;
derive a second candidate intra prediction mode based on a second neighboring block of the current block;
construct an intra prediction mode candidate list of the current block based on the first candidate intra prediction mode and the second candidate intra prediction mode;
determine an intra prediction mode for the current block based on the intra prediction mode candidate list; and
generate the prediction samples for the current block based on the intra prediction mode,
wherein the first neighboring block is a left neighboring block located at the lowermost side among neighboring blocks adjacent to a left boundary of the current block,
wherein the second neighboring block is an upper neighboring block located at the rightmost side among neighboring blocks adjacent to an upper boundary of the current block,
wherein, based on a determination that a size of the current block is W×H, and x and y components of a top-left sample position of the current block are xN and yN respectively, the first neighboring block is a block including a sample at the coordinates of (xN−1, yN+H−1), and the second neighboring block is a block including a sample at the coordinates of (xN+W−1, yN−1), and
wherein the at least one processor configured to construct the intra prediction mode candidate list comprises the at least one processor configured to:
determine whether the first candidate intra prediction mode is equal to the second candidate intra prediction mode, and
determine whether a mode value of the first candidate intra prediction mode or a mode value of the second candidate intra prediction mode is greater than a mode value of a DC intra prediction mode.
3. An apparatus for transmitting data for an image, the apparatus comprising:
at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on determining that an intra prediction is applied for a current block; performing the intra prediction for the current block to generate prediction samples; generating residual samples for the current block based on prediction samples for the current block; and encoding the image information including prediction information including an MPM index related to the intra prediction to output the bitstream, and
a transmitter configured to transmit the data comprising the bitstream,
wherein the performing the intra prediction for the current block comprising:
deriving a first candidate intra prediction mode based on a first neighboring block of the current block;
deriving a second candidate intra prediction mode based on a second neighboring block of the current block;
constructing an intra prediction mode candidate list of the current block based on the first candidate intra prediction mode and the second candidate intra prediction mode;
deriving an intra prediction mode for the current block based on the intra prediction mode candidate list; and
generating the prediction samples for the current block based on the intra prediction mode,
wherein the first neighboring block is a left neighboring block located at the lowermost side among neighboring blocks adjacent to a left boundary of the current block,
wherein the second neighboring block is an upper neighboring block located at the rightmost side among neighboring blocks adjacent to an upper boundary of the current block,
wherein, based on a determination that a size of the current block is W×H, and x and y components of a top-left sample position of the current block are xN and yN respectively, the first neighboring block is a block including a sample at the coordinates of (xN−1, yN+H−1), and the second neighboring block is a block including a sample at the coordinates of (xN+W−1, yN−1), and
wherein the constructing the intra prediction mode candidate list comprising:
determining whether the first candidate intra prediction mode is equal to the second candidate intra prediction mode, and
determining whether a mode value of the first candidate intra prediction mode or a mode value of the second candidate intra prediction mode is greater than a mode value of a DC intra prediction mode.