Method and device for performing image decoding on basis of intra prediction in image coding system

1. An image decoding method performed by a decoding device, the method comprising:

obtaining prediction mode information and residual information for a current block from a bitstream;

constructing a Most Probable Mode (MPM) list for the current block based on an intra prediction mode of a neighboring block of the current block;

deriving an intra-prediction mode of the current block based on the prediction mode information and the MPM list;

deriving neighboring samples including left neighboring samples and upper neighboring samples of the current block;

deriving reference samples for prediction of a target sample of the current block among the neighboring samples based on a position of the target sample and a prediction angle of the intra-prediction mode;

determining an interpolation filter for the target sample based on the intra-prediction mode and a size of the current block, wherein the interpolation filter is determined as one of a Gaussian filter and a cubic filter;

deriving a prediction sample of the target sample based on the interpolation filter and the reference samples;

deriving a residual sample of the target sample based on the residual information; and

generating a reconstructed picture based on the prediction sample and the residual sample,

wherein determining the interpolation filter for the target sample based on the intra-prediction mode and the size of the current block comprises:

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 the intra-prediction mode is one of directional intra prediction modes with a prediction angle greater than 0,

wherein based on the size of the current block being greater than or equal to the first specific value, the interpolation filter for the target sample is derived as the 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 for the target sample is derived as the 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 for the target sample is derived as the Gaussian filter.

2. An image encoding method performed by an encoding device, the method comprising:

constructing a Most Probable Mode (MPM) list for a current block based on an intra prediction mode of a neighboring block of the current block;

determining an intra-prediction mode of the current block based on the MPM list;

deriving neighboring samples including left neighboring samples and upper neighboring samples of the current block;

deriving reference samples for prediction of a target sample of the current block among the neighboring samples based on a position of the target sample and a prediction angle of the intra-prediction mode;

determining an interpolation filter for the target sample based on the intra-prediction mode and a size of the current block, wherein the interpolation filter is determined as one of a Gaussian filter and a cubic filter;

deriving a prediction sample of the target sample based on the interpolation filter and the reference samples;

deriving a residual sample of the target sample based on the prediction sample; and

encoding a bitstream including prediction mode information for the current block representing the intra-prediction mode of the current block among MPM candidates of the MPM list, and residual information for the residual sample,

wherein determining the interpolation filter for the target sample based on the intra-prediction mode and the size of the current block comprises:

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 the intra-prediction mode is one of directional intra prediction modes with a prediction angle greater than 0,

wherein based on the size of the current block being greater than or equal to the first specific value, the interpolation filter for the target sample is derived as the 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 for the target sample is derived as the 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 for the target sample is derived as the Gaussian filter.

3. A non-transitory computer-readable storage medium storing the bitstream encoded by the image encoding method of claim 2 .

4. A transmission method of data for image, the method comprising:

obtaining a bitstream of image information including prediction mode information and residual information for a current block; and

transmitting the data including the bitstream of the video information including the prediction mode information and the residual information,

wherein the prediction mode information for the current block represents an intra-prediction mode of the current block among Most Probable Mode (MPM) candidates of a MPM list,

wherein the MPM list for the current block is constructed based on an intra prediction mode of a neighboring block of the current block, and the intra-prediction mode of the current block is determined based on the MPM list,

wherein a prediction sample of a target sample of the current block is derived based on an interpolation filter and reference samples of the target sample among neighboring samples of the current block,

wherein the residual information is generated based on a residual sample of a target sample for the current block,

wherein the residual sample is derived based on a prediction sample of the target sample derived by performing intra-prediction,

wherein the interpolation filter for the target sample is determined based on the intra-prediction mode and a size of the current block,

wherein determining the interpolation filter for the target sample comprises:

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 the intra-prediction mode is one of directional intra prediction modes with a prediction angle greater than 0,

wherein based on the size of the current block being greater than or equal to the first specific value, the interpolation filter for the target sample is derived as the 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 for the target sample is derived as the 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 for the target sample is derived as the Gaussian filter.