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. A video decoding method performed by a video decoder, comprising:
deriving a prediction mode of a current block as an intra planar prediction mode;
deriving neighboring reference samples of the current block, wherein the reference samples include left reference samples and upper reference samples;
deriving a prediction sample of the current block based on the neighboring reference samples; and
generating a reconstructed picture based on the prediction sample;
wherein the prediction sample is derived based on bi-linear interpolation using 4 reference samples among the neighboring reference samples,
wherein the 4 reference samples include a first reference sample located in the 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, and
wherein the second reference sample is derived by using a sample located in a lower side of a lowest sample among the left reference samples adjacent to a left boundary of the current block, and the fourth reference sample is derived by using a sample located in a right side of a right-most sample among the upper reference samples adjacent to an upper boundary of the current block.
2. The video decoding 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.
3. The video decoding 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 video decoding method of claim 2 , wherein the adjacent samples of the fourth reference sample which is an nth upper reference sample include an (n−1)th upper reference sample and an (n+1)th upper reference sample.
5. The video decoding method of claim 2 , wherein the adjacent samples of the second reference sample which is an nth left reference pixel include an (n−1)th left reference sample and an (n+1)th left reference sample.
6. The video decoding method of claim 4 , wherein a 3-tap filter is applied to the fourth reference sample,
wherein the 3-tap filter has a weight of 1 to the (n+1)th upper reference sample, a weight of 2 to the fourth reference sample, and a weight of 1 to the (n+1)th upper reference sample.