Intra interpolation filter for multi-line intra prediction

1. A method for selecting an intra interpolation filter for multi-line intra prediction based on a reference line index for decoding a video sequence, comprising:

identifying a set of reference lines associated with a coding unit;

applying an edge smoothing filter or an edge preserving filter to reference samples included in a first reference line, of the set of reference lines, that is adjacent to the coding unit to generate a first set of prediction samples based on the first reference line being associated with a first reference line index having a value of zero; and

applying only an edge preserving filter to reference samples included in a second reference line, of the set of reference lines, that is non-adjacent to the coding unit to generate a second set of prediction samples based on the second reference line being associated with a second reference line index having a non-zero value,

wherein when a first type of edge preserving filter is applied to the first reference line, a second type of edge preserving filter that is different than the first type of edge preserving filter is applied to the second reference line, and

wherein the edge smoothing filter is applied in association with wide angle modes of the first reference line, and wherein the edge preserving filter is applied to wide angle modes of the second reference line.

2. The method of claim 1 , wherein an edge smoothing filter is a linear interpolation filter having only positive or zero filter coefficients, and

wherein an edge preserving filter is at least one of a linear interpolation filter having at least one or two negative filter coefficients or a non-linear filter.

3. The method of claim 1 , wherein the edge smoothing interpolation filter comprises a bilinear filter or a Gaussian filter.

4. The method of claim 2 , wherein the edge preserving filter comprises at least one of a Cubic filter, a discrete cosine transform (DCT)-based filter, a polynomial-based interpolation filter, a bilateral filter, and a Hermite interpolation filter.

5. The method of claim 1 , wherein an M-tap edge preserving filter is applied to the first reference line, an N-tap interpolation filter is applied to the second reference line, and M is not equal to N.

6. The method of claim 1 , wherein a first edge preserving filter associated with a first set of filter coefficients is applied to the first reference line, and wherein a second edge preserving filter associated with a second set of filter coefficients that is different than the first set of filter coefficients is applied to the second reference line.

7. The method of claim 1 , wherein an edge preserving filter including fixed filter coefficients is applied to the first reference line.

8. The method of claim 1 , further comprising:

applying the edge smoothing filter or the edge preserving filter to the reference samples included in the first reference line, of the set of reference lines, that is adjacent to the coding unit to generate the first set of prediction samples based on the first reference line; and

applying the edge preserving filter to the second reference line, of the set of reference lines, that is non-adjacent to the coding unit to generate the second set of prediction samples.

9. A device for selecting an intra interpolation filter for multi-line intra prediction based on a reference line index for decoding a video sequence, comprising:

at least one memory configured to store program code;

at least one processor configured to read the program code and operate as instructed by the program code, the program code including:

identifying code configured to cause the at least one processor to identify a set of reference lines associated with a coding unit;

first applying code configured to cause the at least one processor to apply an edge smoothing filter and an edge preserving filter to reference samples included in a first reference line, of the set of reference lines, that is adjacent to the coding unit to generate a first set of prediction samples based on the first reference line being associated with a first reference line index having a value of zero; and

second applying code configured to cause the at least one processor to apply an edge preserving filter to reference samples included in a second reference line, of the set of reference lines, that is non-adjacent to the coding unit to generate a second set of prediction samples based on the second reference line being associated with a second reference line index having a non-zero value,

wherein when a first edge preserving filter associated with a first set of filter coefficients is applied to the first reference line, a second edge preserving filter associated with a second set of filter coefficients that is different than the first set of filter coefficients is applied to the second reference line, and

wherein the edge smoothing filter is applied in association with wide angle modes of the first reference line, and wherein the edge preserving filter is applied to wide angle modes of the second reference line.

10. The device of claim 9 , wherein an edge smoothing filter is a linear interpolation filter having only positive or zero filter coefficients, and

wherein an edge preserving filter is at least one of a linear interpolation filter having at least one or two negative filter coefficients or a non-linear filter.

11. The device of claim 9 , wherein an edge smoothing interpolation filter that comprises a bilinear filter or a Gaussian filter is applied to the first reference line.

12. The device of claim 9 , wherein an edge preserving interpolation filter that comprises at least one of a Cubic filter, a discrete cosine transform (DCT)-based filter, a polynomial-based interpolation filter, a bilateral filter, and a Hermite interpolation filter is applied to the first reference line.

13. The device of claim 9 , wherein a first type of edge preserving filter is applied to the first reference line, and wherein a second type of edge preserving filter that is different than the first type of edge preserving filter is applied to the second reference line.

14. The device of claim 9 , wherein an M-tap edge preserving filter is applied to the first reference line, an N-tap interpolation filter is applied to the second reference line, and M is not equal to N.

15. The device of claim 9 , wherein an edge preserving filter including fixed filter coefficients is applied to the first reference line.

16. The device of claim 9 , wherein the edge smoothing filter is applied in association with wide angle modes of the first reference line, and wherein the edge preserving filter is applied to wide angle modes of the second reference line.

17. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by one or more processors of a device for selecting an intra interpolation filter for multi-line intra prediction based on a reference line index for decoding a video sequence, cause the one or more processors to:

identify a set of reference lines associated with a coding unit;

apply an edge smoothing filter or an edge preserving filter to reference samples included in a first reference line, of the set of reference lines, that is adjacent to the coding unit to generate a first set of prediction samples based on the first reference line being associated with a first reference line index having a value of zero; and

apply only an edge preserving filter to reference samples included in a second reference line, of the set of reference lines, that is non-adjacent to the coding unit to generate a second set of prediction samples based on the second reference line being associated with a second reference line index having a non-zero value,

wherein the edge smoothing filter is applied in association with wide angle modes of the first reference line, and wherein the edge preserving filter is applied to wide angle modes of the second reference line.