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 comprising:
receiving a bitstream including information on a picture to be decoded;
determining whether intra prediction or inter prediction is applied to a current block based on prediction mode information acquired by entropy-decoding the bitstream;
deriving an intra prediction mode for the current block when intra prediction is applied to the current block;
deriving neighboring samples used for intra prediction of the current block, wherein the neighboring samples include left side samples of the current block and upper side samples of the current block, wherein filtering is applied to at least one of the neighboring samples;
deriving a prediction sample of the current block based on the derived neighboring samples;
generating a reconstructed picture based on the prediction sample of the current block;
wherein the prediction sample of the current block is derived based on interpolation using four reference samples, two reference samples from the left side samples and two reference samples from the upper side samples, including a first reference sample located in the same row as the prediction sample, a second reference sample pixel located at a lower side of the first reference sample a third reference sample located in the same column as the prediction sample and a fourth reference sample located at a right side of the third reference sample;
wherein the second reference sample has been filtered by using adjacent samples of the second reference sample, and the fourth reference sample has been filtered by using adjacent samples of the fourth reference sample; and
wherein the second reference sample is derived by using a sample located at a lower side of a lowest sample among left samples adjacent to the left boundary of the current block, and the fourth reference sample is derived by using a sample located at a right side of a right-most sample among upper samples adjacent to the upper boundary of the current block.
2. The method of claim 1 ,
wherein 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); and
a filtered value of the second reference sample and a filtered 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 filtered value of the second reference sample, T′ represents the filtered value of the fourth reference sample, and P represents a sample value of a corresponding location.
3. The method of claim 1 , wherein the adjacent samples of the second reference sample include an upper side sample and a lower side sample of the second reference sample, and
wherein the adjacent samples of the fourth reference sample include a left side sample and a right side sample of the fourth reference sample.
4. The method of claim 3 ,
wherein a location of the second reference sample is specified by (−1, y), a location of the upper side sample is specified by (−1, y−1) and a location of the lower side sample is specified by (−1, y+1), and
a location of the fourth reference sample is specified by (x, −1), a location of the left side sample is specified by (x−1, −1) and a location of the right side sample is specified by (x+1, −1).
5. The method of claim 1 , wherein the intra prediction mode of the current block is a planar mode.