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:

• deriving an intra-prediction mode of a current block;
• deriving upper neighboring samples and left neighboring samples of the current block;
• and
• generating a prediction sample of the current block based on the upper neighboring samples and the left neighboring samples and the intra-prediction mode,
• wherein the upper neighboring samples include upper neighboring samples of a n-th row, and
• wherein the left neighboring samples include left neighboring samples of a n-th column.

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
• encoding prediction information of the current block,
• wherein the upper neighboring samples include upper neighboring samples of a n-th row, and
• wherein the left neighboring samples include left neighboring samples of a n-th column.