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

An video encoding method performed by an encoding device, the method comprising:

• determining an intra-prediction mode of a current block, wherein the intra-prediction mode is one of directional intra prediction modes with a prediction angle greater than 0;
• 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;
• and
• encoding video information comprising prediction information for the current block,
• wherein when the size of the current block is greater than or equal to a first specific value, the interpolation filter for the target sample is derived as the Gaussian filter, and
• wherein when the size of the current block is smaller than the first specific value, the interpolation filter for the target sample is derived based on the intra-prediction mode and a second specific value.

A non-transitory computer-readable storage medium storing video information, the video information, when executed, causing a decoding apparatus to perform the following steps:

• deriving an intra-prediction mode of a current block, wherein the intra-prediction mode is one of directional intra prediction modes with a prediction angle greater than 0;
• 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;
• and
• deriving a prediction sample of the target sample based on the interpolation filter and the reference samples,
• wherein when the size of the current block is greater than or equal to a first specific value, the interpolation filter for the target sample is derived as the Gaussian filter, and
• wherein when the size of the current block is smaller than the first specific value, the interpolation filter for the target sample is derived based on the intra-prediction mode and a second specific value.