Intra prediction in image processing

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

determining an intra prediction mode of a current block, wherein the intra prediction mode is determined as a directional prediction mode from intra prediction modes including 33 directional prediction modes and at least one non-directional prediction mode;

deriving neighboring reference samples of the current block;

performing filtering on at least one of the reference samples; and

generating a prediction sample of the current block based on a filtered reference sample,

wherein the filtered reference sample is filtered by using a first reference sample located in a prediction direction of the intra prediction mode with regard to a location of the prediction sample and reference samples adjacent to the first reference sample, and

wherein when the first reference sample is located on an upper side of the current block, the reference samples adjacent to the first reference sample includes a second reference sample located on a left side of the first reference sample and a third reference sample located on a right side of the first reference sample.

2. The method of claim 1 , wherein a filtering coefficient for the first reference sample is greater than filtering coefficients for the reference samples adjacent to the first reference sample.

3. The method of claim 1 , wherein the filtered reference sample is filtered by applying a 3-tap filter with a filtering coefficient of [1 2 1]to the first reference sample.

4. The method of claim 1 , wherein the filtered reference sample is filtered by applying a filtering using a 3-tap filter to the first reference sample, the second reference sample, and the third reference sample to generate the filtered reference sample at the position of the first reference sample.

5. The method of claim 1 , wherein the intra prediction mode is a prediction mode having an up-right diagonal prediction direction.

6. The method of claim 1 , wherein the intra prediction mode is a prediction mode having an up-left diagonal prediction direction o.

7. The method of claim 1 , wherein the intra prediction mode is a prediction mode having a down-left diagonal prediction direction.

8. The method of claim 1 , wherein it is determined whether the filtering is performed depending on a size and the intra prediction mode of the current block.

9. The method of claim 8 , wherein when it is determined that the filtering is not performed, the prediction sample is generated based on the first reference sample, and

wherein a smoothing process using 2-tap coefficients is performed on the first reference sample.

10. The method of claim 1 , wherein the first reference sample is filtered by the following equation:

( r ( x− 1)+2* r ( x )+ r ( x+ 1)+2)>>2,

where r(x) represents a sample value of the first reference sample, r(x−1) represents a sample value of the second reference sample located on the left side of the first reference sample, and r(x+1) represents a sample value of the third reference sample located on the right side of the first reference sample.

11. An image encoding method using intra prediction, by an encoding apparatus, the method comprising:

determining an intra prediction mode of a current block, wherein the intra prediction mode is determined as a directional prediction mode from intra prediction modes including 33 directional prediction modes and at least one non-directional prediction mode;

deriving neighboring reference samples of the current block;

performing filtering on at least one of the reference samples;

generating a prediction sample of the current block based on a filtered reference sample; and

encoding image information including prediction mode information indicating the intra prediction mode of the current block,

wherein the filtered reference sample is filtered by using a first reference sample located in a prediction direction of the intra prediction mode with regard to a location of the prediction sample and reference samples adjacent to the first reference sample, and

wherein when the first reference sample is located on an upper side of the current block, the reference samples adjacent to the first reference sample includes a second reference sample located on a left side of the first reference sample and a third reference sample located on a right side of the first reference sample.

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

determining an intra prediction mode of a current block based on the image information, wherein the intra prediction mode is determined as a directional prediction mode from intra prediction modes including 33 directional prediction modes and at least one non-directional prediction mode;

deriving neighboring reference samples of the current block;

performing filtering on at least one of the reference samples; and

generating a prediction sample of the current block based on a filtered reference sample,

wherein the filtered reference sample is filtered by using a first reference sample located in a prediction direction of the intra prediction mode with regard to a location of the prediction sample and reference samples adjacent to the first reference sample, and

wherein when the first reference sample is located on an upper side of the current block, the reference samples adjacent to the first reference sample includes a second reference sample located on a left side of the first reference sample and a third reference sample located on a right side of the first reference sample.