Intra prediction method and apparatus using the method
An intra prediction method and a device using the intra prediction method are provided. The intra prediction method using a DC mode includes setting a bottom-right pixel to a DC-predicted value, interpolating the bottom-right pixel and an n-th top reference pixel to derive predicted values of an n-th column and interpolating the bottom-right pixel and an n-th left reference pixel to derive predicted values of an n-row, and performing bidirectional linear interpolation to derive predicted values of pixels included in a prediction unit other than the n-th row and the n-th column.
1. A method of image decoding, by a decoding apparatus, comprising: obtaining information on a prediction mode from a bitstream; determining an intra prediction mode for a current block based on the information on the prediction mode; deriving a prediction sample on the current block based on the intra prediction mode and neighboring samples of the current block; and generating a reconstructed sample based on the prediction sample, wherein the prediction sample is derived by using 4 samples among the neighboring samples, wherein the 4 samples include a first sample located in a same column with the prediction sample, a second sample located in a right side of the first sample, a third sample located in a same row with the prediction sample, and a fourth sample located in a lower side of the third sample, wherein the first sample and the second sample are located in an upper side of the current block, and the third sample and the fourth sample are located in a left side of the current block, and wherein the second sample is located in a right side with respect to a right boundary of the current block, and the fourth sample is located in a lower side with respect to a lower boundary of the current block, wherein the second sample is located in a right side of a right-most sample among neighboring samples adjacent to an upper boundary of the current block, and wherein the fourth sample is located in a lower side of a lowest sample among neighboring samples adjacent to a left boundary of the current block.
2. The method of claim 1 , wherein the second sample is located in an upper right side of the current block, and the fourth sample is located in a lower left side of the current block.
3. The method of claim 1 , wherein when the current block is a block of N×N size (N is integer and N>0), and
wherein the second sample is located at among (N+1)-th through 2N-th, inclusive, sample positions with regard to x-axis in the upper side of the current block, and the fourth sample is located at among (N+1)-th through 2N-th, inclusive, sample positions with regard to y-axis in the left side of the current block.
4. The method of claim 3 , wherein the second sample is located at the 2N-th sample position with regard to the x-axis in the upper side of the current block, and the fourth sample is located at the 2N-th sample position with regard to the y-axis in the left side of the current block.
5. The method of claim 1 , wherein the prediction sample in the current block is derived based on the bi-directional interpolation according to a distance between the prediction sample and the first sample, a distance between the prediction sample and the second sample, a distance between the prediction sample and the third sample and a distance between the prediction sample and the fourth sample.
6. The method of claim 5 , wherein weight is applied to each of the values of the 4 samples which is used for the bi-directional interpolation.
7. The method of claim 1 , wherein the prediction sample in the current block is derived based on the bi-directional interpolation according to a vertical distance between the prediction sample and the first sample, a vertical distance between the prediction sample and the fourth sample, a horizontal distance between the prediction sample and the second sample, and a horizontal distance between the prediction sample and the third sample.
8. A decoding apparatus for image decoding, comprising: an entropy decoding module configured to obtain information on a prediction mode from a bitstream; a prediction module configured to determine an intra prediction mode for a current block based on the information on the prediction mode, to derive a prediction sample on the current block based on the intra prediction mode and neighboring samples of the current block; and an adder module configured to generate a reconstructed sample based on the prediction sample, wherein the prediction module derives the prediction sample by using 4 samples among the neighboring samples, wherein the 4 samples include a first sample located in a same column with the prediction sample, a second sample located in a right side of the first sample, a third sample located in a same row with the prediction sample, and a fourth sample located in a lower side of the third sample, wherein the first sample and the second sample are located in an upper side of the current block and the third sample and the fourth sample are located in a left side of the current block, and wherein the second sample is located in a right side with respect to a right boundary of the current block, and the fourth sample is located in a lower side with respect to a lower boundary of the current block, wherein the second sample is located in a right side of a right-most sample among neighboring samples adjacent to an upper boundary of the current block, wherein the fourth sample is located in a lower side of a lowest sample among neighboring samples adjacent to a left boundary of the current block.
9. The apparatus of claim 8 , wherein the second sample is located in an upper right side of the current block, and the fourth sample is located in a lower left side of the current block.
10. The apparatus of claim 8 , wherein when the current block is a block of N×N size (N is integer and N>0),
wherein the second sample is located at among (N+1)-th through 2N-th, inclusive, sample positions with regard to an x-axis in the upper side of the current block, and the fourth sample is located at among (N+1)-th through 2N-th, inclusive, sample positions with regard to a y-axis in the left side of the current block.
11. The apparatus of claim 10 , wherein the second sample is located at the 2N-th sample position with regard to the x-axis in the upper side of the current block, and the fourth sample is located at the 2N-th sample position with regard to the y-axis in the left side of the current block.
12. The apparatus of claim 8 , wherein the prediction module derives the prediction sample based on the bi-directional interpolation according to a distance between the prediction sample and the first sample, a distance between the prediction sample and the second sample, a distance between the prediction sample and the third sample and a distance between the prediction sample and the fourth sample.
13. The apparatus of claim 12 , wherein weight is applied to each of the values of the 4 samples which is used for the bi-directional interpolation.
14. The apparatus of claim 8 , wherein the prediction module derives the prediction sample based on the bi-directional interpolation according to a vertical distance between the prediction sample and the first sample, a vertical distance between the prediction sample and the fourth sample, a horizontal distance between the prediction sample and the second sample, and a horizontal distance between the prediction sample and the third sample.