Filters for motion compensation interpolation with reference down-sampling
The present disclosure provides systems and methods for processing video content using motion compensation interpolation. The methods include: in response to a target picture and a reference picture having different resolutions, applying a band-pass filter to the reference picture, to perform a motion compensated interpolation with reference down-sampling to generate a reference block; and encoding or decoding a block of the target picture using the reference block.
1. A computer-implemented method for performing motion compensation interpolation, comprising:
in response to a target picture and a reference picture having different resolutions, applying a band-pass filter to the reference picture, to perform a motion compensated interpolation with reference down-sampling to process a block of the target picture, wherein the band-pass filter has a kernel function based on a ratio between the resolutions of the target picture and the reference picture.
2. The method according to claim 1 , wherein the band-pass filter is a cosine windowed-sinc filter generated based on an ideal low-pass filter and a window function.
3. The method according to claim 2 , wherein the cosine windowed-sinc filter is based on a kernel function
f
(
n
)
=
f
c
r
Sin
c
(
f
c
r
n
)
cos
(
π
n
L
-
1
)
,
wherein
n
=
-
L
-
1
2
,
…
,
L
-
1
2
,
wherein fc is a cutoff frequency of the cosine windowed-sinc filter, L is a kernel length, and r is a down-sampling ratio of the reference down-sampling.
4. The method according to claim 1 , further comprising:
obtaining real filter coefficients of the band-pass filter;
determining a plurality of rounding directions for the real filter coefficients, respectively;
generating a plurality of combinations of rounded filter coefficients by rounding the real filter coefficients according to the plurality of rounding directions; and
selecting, among the plurality of combinations, a combination of rounded filter coefficients that causes a cost function to be minimum or maximum.
5. The method according to claim 4 , wherein the cost function is associated with the rounded filter coefficients and a reference.
6. The method according to claim 5 , wherein
the reference is the real filter coefficients of the band-pass filter before the rounding, a frequency response of an ideal filter, or a frequency response of a filter having a longer length than the band-pass filter.
7. The method according to claim 2 , wherein the cosine windowed-sinc filter is an 8-tap filter, a 6-tap filter, or a 4-tap filter.
8. The method according to claim 1 , wherein applying the band-pass filter to the reference picture comprises:
obtaining a luma sample or a chroma sample at a fractional sample position.
9. The method according to claim 1 , further comprising:
determining the band-pass filter to be one of an 8-tap filter, a 6-tap filter, and a 4-tap filter, based on a ratio between the resolution of the reference picture and the resolution of the target picture.
10. The method according to claim 4 , further comprising:
signaling the selected combination of rounded filter coefficients of the band-pass filter in at least one of Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), an Adaptation Parameter Set (APS), and a slice header.
11. A system for performing motion compensation interpolation, comprising:
a memory storing a set of instructions; and
at least one processor configured to execute set of instructions to cause the system to perform:
in response to a target picture and a reference picture having different resolutions, applying a band-pass filter to the reference picture, to perform a motion compensated interpolation with reference down-sampling to process a block of the target picture, wherein the band-pass filter has a kernel function based on a ratio between the resolutions of the target picture and the reference picture.
12. The system according to claim 11 , wherein the band-pass filter is a cosine windowed-sinc filter generated based on an ideal low-pass filter and a window function.
13. The system according to claim 12 , wherein the cosine windowed-sinc filter is based on a kernel function
f
(
n
)
=
f
c
r
Sin
c
(
f
c
r
n
)
cos
(
π
n
L
-
1
)
,
wherein
n
=
-
L
-
1
2
,
…
,
L
-
1
2
,
fc being a cutoff frequency of the cosine windowed-sinc filter, L being a kernel length, and r being a down-sampling ratio of the reference down-sampling.
14. The system according to claim 11 , wherein at least one processor configured to execute set of instructions to cause the system to further perform:
obtaining real filter coefficients of the band-pass filter;
determining a plurality of rounding directions for the real filter coefficients, respectively;
generating a plurality of combinations of rounded filter coefficients by rounding the real filter coefficients according to the plurality of rounding directions; and
selecting, among the plurality of combinations, a combination of rounded filter coefficients that causes a cost function to be minimum or maximum.
15. The system according to claim 14 , wherein the cost function is associated with the rounded filter coefficients and a reference.
16. The system according to claim 15 , wherein
the reference is the real filter coefficients of the band-pass filter before the rounding, a frequency response of an ideal filter, or a frequency response of a filter having a longer length than the band-pass filter.
17. The system according to claim 12 , wherein the cosine windowed-sinc filter is an 8-tap filter, a 6-tap filter, or a 4-tap filter.
18. The system according to claim 11 , wherein applying the band-pass filter to the reference picture comprises:
obtaining a luma sample or a chroma sample at a fractional sample position.
19. The system according to claim 11 , wherein at least one processor configured to execute set of instructions to cause the system to further perform:
determining the band-pass filter to be one of an 8-tap filter, a 6-tap filter, and a 4-tap filter, based on a ratio between the resolution of the reference picture and the resolution of the target picture.
20. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computer system to cause the computer system to perform a method for processing video content, the method comprising:
in response to a target picture and a reference picture having different resolutions, applying a band-pass filter to the reference picture, to perform a motion compensated interpolation with reference down-sampling to process a block of the target picture, wherein the band-pass filter has a kernel function based on a ratio between the resolutions of the target picture and the reference picture.