Image decoding method and apparatus relying on intra prediction in image coding system

A method of decoding video performed by a decoding device, the method comprising:

• receiving information on an intra prediction mode for a current block;
• determining the intra prediction mode for the current block based on the information on the intra prediction mode;
• deriving upper neighboring samples and left neighboring samples of the current block;
• deriving a prediction sample of the current block based on the upper neighboring samples and the left neighboring samples and the intra-prediction mode;
• and
• generating a reconstructed block using the derived prediction sample,
• wherein the upper neighboring samples include upper neighboring samples of a n-th row,
• wherein the left neighboring samples include left neighboring samples of a n-th column,
• wherein the n is more than 1, and
• wherein based on an upper neighboring sample which is derived based on a prediction direction of the current block and is positioned at a fractional sample position, a sample value of the upper neighboring sample positioned at the fractional sample position is derived through linear interpolation between sample values of samples positioned at integer sample positions which are adjacent to the left and right of the upper neighboring sample positioned at the fractional sample position.

A method of encoding video performed by an encoding device, the method comprising:

• determining an intra-prediction mode of a current block;
• deriving upper neighboring samples and left neighboring samples of the current block;
• generating a prediction sample of the current block based on the upper reference samples and the left reference samples and the intra-prediction mode;
• and
• generating prediction mode information based on the determined intra prediction mode;
• encoding image information including the prediction mode information to generate a bitstream,
• wherein the upper neighboring samples include upper neighboring samples of a n-th row,
• wherein the left neighboring samples include left neighboring samples of a n-th column,
• wherein the n is more than 1, and
• wherein based on an upper neighboring sample which is derived based on a prediction direction of the current block and is positioned at a fractional sample position, a sample value of the upper neighboring sample positioned at the fractional sample position is derived through linear interpolation between sample values of samples positioned at integer sample positions which are adjacent to the left and right of the upper neighboring sample positioned at the fractional sample position.

A non-transitory computer-readable storage medium storing encoded video data comprising information on instructions, when executed, causing a video decoding device to perform operations comprising:

• receiving information on an intra prediction mode for a current block;
• determining the intra prediction mode for the current block based on the information on the intra prediction mode;
• deriving upper neighboring samples and left neighboring samples of the current block;
• deriving a prediction sample of the current block based on the upper neighboring samples and the left neighboring samples and the intra-prediction mode;
• and
• generating a reconstructed block using the derived prediction sample,
• wherein the upper neighboring samples include upper neighboring samples of a n-th row,
• wherein the left neighboring samples include left neighboring samples of a n-th column,
• wherein the n is more than 1, and
• wherein based on an upper neighboring sample which is derived based on a prediction direction of the current block and is positioned at a fractional sample position, a sample value of the upper neighboring sample positioned at the fractional sample position is derived through linear interpolation between sample values of samples positioned at integer sample positions which are adjacent to the left and right of the upper neighboring sample positioned at the fractional sample position.