Method and device for performing image decoding on basis of intra prediction in image coding system
A method by which a decoding device performs image decoding, according to the present invention, comprises the steps of: deriving an intra prediction mode of a current block; deriving neighboring samples including left neighboring samples and upper neighboring samples of the current block; deriving reference samples for prediction of a target sample among the neighboring samples on the basis of the position of the target sample of the current block and the prediction angle of the intra prediction mode; determining an interpolation filter for the target sample; and deriving the prediction sample of the target sample on the basis of the interpolation filter and the reference samples.
1. An image decoding method performed by a decoding device, the method comprising:
obtaining prediction mode information for a current block from a bitstream;
deriving an intra prediction mode of an upper neighboring block of the current block and an intra prediction mode of a left neighboring block of the current block;
constructing a Most Probable Mode (MPM) list for the current block based on the intra prediction mode of the upper neighboring block and the intra prediction mode of the left neighboring block;
deriving an MPM candidate indicated by the prediction mode information among MPM candidates in the MPM list as the intra prediction mode of the current block;
deriving neighboring samples including left neighboring samples and upper neighboring samples of the current block;
deriving reference samples for prediction of a target sample among the neighboring samples, based on a position of the target sample of the current block and a prediction angle of the intra prediction mode;
determining an interpolation filter applied to the reference samples based on the intra prediction mode and a size of the current block;
deriving a predicted sample of the target sample based on the interpolation filter and the reference samples; and
generating a reconstructed picture based on the prediction sample,
wherein determining the interpolation filter applied to the reference samples based on the intra prediction mode and the size of the current block comprises:
determining whether the intra prediction mode of the current block is a directional intra prediction mode;
based on the intra prediction mode of the current block being the directional intra prediction mode, determining whether the size of the current block is smaller than a first specific value; and
based on the size of the current block being smaller than the first specific value, determining whether the prediction angle of the intra prediction mode is smaller than a second specific value,
wherein based on the size of the current block being not smaller than the first specific value, the interpolation filter is derived as a Gaussian filter,
wherein based on the size of the current block being smaller than the first specific value and the prediction angle of the intra prediction mode being smaller than the second specific value, the interpolation filter is derived as a cubic filter, and
wherein based on the size of the current block being smaller than the first specific value and the prediction angle of the intra prediction mode being not smaller than the second specific value, the interpolation filter is derived as the Gaussian filter.
2. An image encoding method performed by an encoding device, the method comprising:
deriving an intra prediction mode of an upper neighboring block of a current block and an intra prediction mode of a left neighboring block of the current block;
constructing a Most Probable Mode (MPM) list for the current block based on the intra prediction mode of the upper neighboring block and the intra prediction mode of the left neighboring block;
deriving an MPM candidate selected from among MPM candidates in the MPM list as an intra prediction mode of the current block;
deriving neighboring samples including left neighboring samples and upper neighboring samples of the current block;
deriving reference samples for prediction of a target sample among the neighboring samples, based on a position of the target sample of the current block and a prediction angle of the intra prediction mode;
determining an interpolation filter applied to the reference samples based on the intra prediction mode and a size of the current block;
deriving a prediction sample of the target sample based on the interpolation filter and the reference samples; and
encoding image information including prediction mode information indicating the selected MPM candidate,
wherein determining the interpolation filter applied to the reference samples based on the intra prediction mode and the size of the current block comprises:
determining whether the intra prediction mode of the current block is a directional intra prediction mode;
based on the intra prediction mode of the current block being the directional intra prediction mode, determining whether the size of the current block is smaller than a first specific value; and
based on the size of the current block being smaller than the first specific value, determining whether the prediction angle of the intra prediction mode is smaller than a second specific value,
wherein based on the size of the current block being not smaller than the first specific value, the interpolation filter is derived as a Gaussian filter,
wherein based on the size of the current block being smaller than the first specific value and the prediction angle of the intra prediction mode being smaller than the second specific value, the interpolation filter is derived as a cubic filter, and
wherein based on the size of the current block being smaller than the first specific value and the prediction angle of the intra prediction mode being not smaller than the second specific value, the interpolation filter is derived as the Gaussian filter.
3. A non-transitory computer-readable storage medium storing a bitstream including the image information encoded by the image encoding method of claim 2 .
4. A transmission method of data for image information, the method comprising:
obtaining a bitstream of the image information including prediction mode information indicating a selected Most Probable Mode (MPM) candidate in a MPM list for a current block, wherein the prediction mode information is generated by performing deriving an intra prediction mode of an upper neighboring block of a current block and an intra prediction mode of a left neighboring block of the current block, constructing the MPM list for the current block based on the intra prediction mode of the upper neighboring block and the intra prediction mode of the left neighboring block, deriving the selected MPM candidate among MPM candidates in the MPM list as an intra prediction mode of the current block, deriving neighboring samples including left neighboring samples and upper neighboring samples of the current block, deriving reference samples for prediction of a target sample among the neighboring samples, based on a position of the target sample of the current block and a prediction angle of the intra prediction mode, determining an interpolation filter applied to the reference samples based on the intra prediction mode and a size of the current block, deriving a prediction sample of the target sample based on the interpolation filter and the reference samples, and generating prediction mode information indicating the selected MPM candidate; and
transmitting the data including the bitstream of the image information including the prediction mode information
wherein determining the interpolation filter applied to the reference samples based on the intra prediction mode and the size of the current block comprises:
determining whether the intra prediction mode of the current block is a directional intra prediction mode;
based on the intra prediction mode of the current block being the directional intra prediction mode, determining whether the size of the current block is smaller than a first specific value; and
based on the size of the current block being smaller than the first specific value, determining whether the prediction angle of the intra prediction mode is smaller than a second specific value,
wherein based on the size of the current block being not smaller than the first specific value, the interpolation filter is derived as a Gaussian filter,
wherein based on the size of the current block being smaller than the first specific value and the prediction angle of the intra prediction mode being smaller than the second specific value, the interpolation filter is derived as a cubic filter, and
wherein based on the size of the current block being smaller than the first specific value and the prediction angle of the intra prediction mode being not smaller than the second specific value, the interpolation filter is derived as the Gaussian filter.