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. An image decoding method, 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 neighboring reference samples of the current block;
generating a prediction sample of the current block based on the intra prediction mode and 4 samples among the neighboring reference samples; and
generating a reconstructed sample based on the prediction sample,
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 neighboring reference 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 reference 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, 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.
3. The method of claim 1 , wherein the right-most sample among the neighboring reference samples adjacent to the upper boundary of the current block is located in a same column with a sample position adjacent to a left side of a right boundary of the current block, and
wherein the lowest sample among the neighboring reference samples adjacent to the left boundary of the current block is located in a same row with a sample position adjacent to an upper side of a bottom boundary 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 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,
wherein the right-most sample among the neighboring samples adjacent to the upper boundary of the current block is located at N-th sample position with regard to x-axis, and
wherein the lowest sample among the neighboring samples adjacent to the left boundary of the current block is located at N-th sample position with regard to y-axis.
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 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 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. An image encoding method, comprising:
determining an intra prediction mode for a current block;
generating information on a prediction mode based on the determined intra prediction mode;
deriving neighboring reference samples of the current block;
generating a prediction sample in the current block based on the intra prediction mode and 4 samples among the neighboring reference samples;
deriving a residual sample in the current block based on the prediction sample; and
generating a bitstream by encoding image information including the information on the prediction mode and information on the residual sample,
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 neighboring reference 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 reference samples adjacent to a left boundary of the current block.
10. The method 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, 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.
11. The method of claim 9 , wherein the right-most sample among the neighboring reference samples adjacent to the upper boundary of the current block is located in a same column with a sample position adjacent to a left side of a right boundary of the current block, and
wherein the lowest sample among the neighboring reference samples adjacent to the left boundary of the current block is located in a same row with a sample position adjacent to an upper side of a bottom boundary of the current block.
12. The method 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 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,
wherein the right-most sample among the neighboring reference samples adjacent to the upper boundary of the current block is located at N-th sample position with regard to x-axis, and
wherein the lowest sample among the neighboring reference samples adjacent to the left boundary of the current block is located at N-th sample position with regard to y-axis.
13. The method 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 method of claim 9 , wherein the prediction sample 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.
15. The method of claim 9 , wherein the prediction sample 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.
16. A non-transitory decoder-readable storage medium storing a bitstream generated by performing the steps of:
determining an intra prediction mode for a current block; generating information on a prediction mode based on the determined intra prediction mode;
deriving neighboring reference samples of the current block;
generating a prediction sample in the current block based on the intra prediction mode and 4 samples among the neighboring reference samples;
deriving a residual sample in the current block based on the prediction sample; and
generating the bitstream by encoding image information including the information on the prediction mode and information on the residual sample,
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 neighboring reference 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 reference samples adjacent to a left boundary of the current block.