Intra-prediction method using filtering, and apparatus using the method

An intra prediction method performed by a decoding apparatus, the method comprising:

• determining, by the decoding apparatus, an intra prediction mode for a current block as an intra planar prediction mode;
• deriving, by the decoding apparatus, neighboring reference samples of the current block;
• and
• generating, by the decoding apparatus, prediction samples of the current block based on the neighboring reference samples,
• wherein a prediction sample of the current block is derived based on four reference samples among the neighboring reference samples,
• wherein the four reference samples include a first reference sample located in a same row with the prediction sample, a second reference sample located in a lower side of the first reference sample, a third reference sample located in a same column with the prediction sample, and a fourth reference sample located in a right side of the third reference sample,
• wherein the second reference sample is located in a same column with the first reference sample and the fourth reference sample is located in a same row with the third reference sample, and
• wherein the second reference sample is derived based on a sample located in a lower side of a lowest sample among left reference samples adjacent to a left boundary of the current block, and the fourth reference sample is derived based on a sample located in a right side of a right-most sample among upper reference samples adjacent to an upper boundary of the current block.

An intra prediction method performed by an encoding apparatus, the method comprising:

• determining, by the encoding apparatus, an intra prediction mode for a current block as an intra planar prediction mode;
• deriving, by the encoding apparatus, neighboring reference samples of the current block;
• and
• generating, by the encoding apparatus, prediction samples of the current block based on the neighboring reference samples,
• wherein a prediction sample of the current block is derived based on four reference samples among the neighboring reference samples,
• wherein the four reference samples include a first reference sample located in a same row with the prediction sample, a second reference sample located in a lower side of the first reference sample, a third reference sample located in a same column with the prediction sample, and a fourth reference sample located in a right side of the third reference sample,
• wherein the second reference sample is located in a same column with the first reference sample and the fourth reference sample is located in a same row with the third reference sample, and
• wherein the second reference sample is derived based on a sample located in a lower side of a lowest sample among left reference samples adjacent to a left boundary of the current block, and the fourth reference sample is derived based on a sample located in a right side of a right-most sample among upper reference samples adjacent to an upper boundary of the current block.

A non-transitory computer readable storage medium storing information causing a decoding apparatus to performs operations comprising:

• determining an intra prediction mode for a current block as an intra planar prediction mode, deriving neighboring reference samples of the current block, and generating prediction samples of the current block based on the neighboring reference samples, wherein a prediction sample of the current block is derived based on 4 reference samples among the neighboring reference samples, wherein the four reference samples include a first reference sample located in a same row with the prediction sample, a second reference sample located in a lower side of the first reference sample, a third reference sample located in a same column with the prediction sample, and a fourth reference sample located in a right side of the third reference sample, wherein the second reference sample is located in a same column with the first reference sample and the fourth reference sample is located in a same row with the third reference sample, and wherein the second reference sample is derived based on a sample located in a lower side of a lowest sample among left reference samples adjacent to a left boundary of the current block, and the fourth reference sample is derived based on a sample located in a right side of a right-most sample among upper reference samples adjacent to an upper boundary of the current block.