Intra prediction method and apparatus based on interpolation
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 filtered neighboring samples by filtering neighboring samples of the current block in a current picture; and
deriving a prediction sample on the current block based on the intra prediction mode and the filtered neighboring samples,
wherein the prediction sample is derived by using 4 samples among the filtered 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 second sample is located in a right side of a right-most sample among filtered 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 filtered neighboring samples adjacent to a left boundary of the current block.
2. The method of claim 1 , 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,
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.
3. 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.
4. The method of claim 1 , 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 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.
5. The method of claim 4 , 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.
6. 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.
7. The method of claim 6 , wherein weight is applied to each of the values of the 4 samples which is used for the bi-directional interpolation.
8. 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.
9. A decoding apparatus for an 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, derive filtered neighboring samples by filtering neighboring samples of the current block in a current picture, and derive a prediction sample on the current block based on the intra prediction mode and the filtered neighboring samples,
wherein the prediction module derives the prediction sample by using 4 samples among the filtered 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 second sample is located in a right side of a right-most sample among filtered 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 filtered neighboring samples adjacent to a left boundary of the current block.
10. The apparatus of claim 9 , 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,
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.
11. The apparatus of claim 9 , 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.
12. The apparatus of claim 9 , 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 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.
13. The apparatus of claim 12 , 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.
14. The apparatus of claim 9 , 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.
15. The apparatus of claim 14 , wherein weight is applied to each of the values of the 4 samples which is used for the bi-directional interpolation.
16. The apparatus of claim 9 , 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.