Intra-prediction method using filtering, and apparatus using the method
Disclosed are an intra-prediction method using filtering and an apparatus using the method. An image-decoding method comprises: a step of filtering an n upper reference pixel of a block to be predicted and neighboring pixels of the n upper reference pixel so as to obtain the filtered n upper reference pixel; and a step of filtering an n left reference pixel of a block to be predicted and neighboring pixels of the n left reference pixel so as to obtain the filtered n left reference pixel. According to the present invention, intra-prediction may be efficiently performed to improve image-encoding/decoding efficiency.
1. 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.
2. The method of claim 1 , wherein the second reference sample is derived by applying filtering using the sample located in the lower side of the lowest sample among the left reference samples adjacent to the left boundary of the current block, and
wherein the fourth reference sample is filtered by using the sample located in the right side of the right-most sample among the upper reference samples adjacent to the upper boundary of the current block.
3. The method of claim 1 , wherein when a location of the second reference sample is specified by (−1, y) and a location of the fourth reference sample is specified by (x, −1), a value of the second reference sample and a value of the fourth reference sample are derived by using the following equations,
L′={P (−1, y− 1)+2× P (−1, y )+ P (−1, y+ 1)+2}/4,
T′={P ( x− 1,−1)+2× P ( x,− 1)+ P ( x+ 1,−1)+2}/4,
where, L′ represents the value of the second reference sample, T′ represents the value of the fourth reference sample, and P represents a sample value of a corresponding location.
4. The method of claim 1 , wherein the second reference sample is derived by applying filtering using adjacent samples of the second reference sample, and the fourth reference sample is filtered by using adjacent samples of the fourth reference sample.
5. The method of claim 4 , wherein the adjacent samples of the fourth reference sample include a sample which is adjacent to a right side of the fourth reference sample and a sample which is adjacent to a left side of the fourth reference sample.
6. The method of claim 5 , wherein a 3-tap filter is applied to the fourth reference sample,
wherein the 3-tap filter has a weight of 1 to the reference sample which is adjacent to a right side of the fourth reference sample, a weight of 2 to the fourth reference sample, and a weight of 1 to the reference sample which is adjacent to a left side of the fourth reference sample.
7. The method of claim 4 , wherein the adjacent samples of the second reference sample include a sample which is adjacent to a lower side of the second reference sample and a sample which is adjacent to an upper side of the second reference sample.
8. The method of claim 7 , wherein a 3-tap filter is applied to the second reference sample,
wherein the 3-tap filter has a weight of 1 to the reference sample which is adjacent to a lower side of the second reference sample, a weight of 2 to the second reference sample, and a weight of 1 to the reference sample which is adjacent to an upper side of the second reference sample.
9. 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.
10. The method of claim 9 , wherein the second reference sample is derived by applying filtering using the sample located in the lower side of the lowest sample among the left reference samples adjacent to the left boundary of the current block, and
wherein the fourth reference sample is filtered by using the sample located in the right side of the right-most sample among the upper reference samples adjacent to the upper boundary of the current block.
11. The method of claim 9 , wherein when a location of the second reference sample is specified by (−1, y) and a location of the fourth reference sample is specified by (x, −1), a value of the second reference sample and a value of the fourth reference sample are derived by using the following equations,
L′={P (−1, y− 1)+2× P (−1, y )+ P (−1, y+ 1)+2}/4,
T′={P ( x− 1,−1)+2× P ( x,− 1)+ P ( x+ 1,−1)+2}/4,
where, L′ represents the value of the second reference sample, T′ represents the value of the fourth reference sample, and P represents a sample value of a corresponding location.
12. The method of claim 9 , wherein the second reference sample is derived by applying filtering using adjacent samples of the second reference sample, and the fourth reference sample is filtered by using adjacent samples of the fourth reference sample.
13. The method of claim 12 , wherein the adjacent samples of the fourth reference sample include a sample which is adjacent to a right side of the fourth reference sample and a sample which is adjacent to a left side of the fourth reference sample.
14. The method of claim 13 , wherein a 3-tap filter is applied to the fourth reference sample,
wherein the 3-tap filter has a weight of 1 to the reference sample which is adjacent to a right side of the fourth reference sample, a weight of 2 to the fourth reference sample, and a weight of 1 to the reference sample which is adjacent to a left side of the fourth reference sample.
15. The method of claim 12 , wherein the adjacent samples of the second reference sample include a sample which is adjacent to a lower side of the second reference sample and a sample which is adjacent to an upper side of the second reference sample.
16. The method of claim 15 , wherein a 3-tap filter is applied to the second reference sample,
wherein the 3-tap filter has a weight of 1 to the reference sample which is adjacent to a lower side of the second reference sample, a weight of 2 to the second reference sample, and a weight of 1 to the reference sample which is adjacent to an upper side of the second reference sample.
17. 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.