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 video decoding method, comprising:
decoding a bitstream to reconstruct a reference picture; and
in response to a target picture and the reference picture having different resolutions, obtaining a chroma Cr sample at a fractional sample position by applying a band-pass filter to the reference picture,
wherein the applying of the band-pass filter performs a motion compensated interpolation with reference down-sampling on the reference picture, the band-pass filter having 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 ƒc 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 2 , wherein the cosine windowed-sinc filter is an 8-tap filter, a 6-tap filter, or a 4-tap filter.
5 . 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.
6 . The method according to claim 5 , wherein the cost function is associated with the rounded filter coefficients and a reference.
7 . The method according to claim 6 , 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.
8 . The method according to claim 5 , further comprising:
encoding the selected combination of rounded filter coefficients of the band-pass filter into at least one of Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), an Adaptation Parameter Set (APS), and a slice header.
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 . A video encoding method, comprising:
in response to a target picture and a reference picture having different resolutions, obtaining a chroma Cr sample at a fractional sample position by applying a band-pass filter to the reference picture; and
encoding the chroma Cr sample,
wherein the applying of the band-pass filter performs a motion compensated interpolation with reference down-sampling on the reference picture, the band-pass filter having a kernel function based on a ratio between the resolutions of the target picture and the reference picture.
11 . The method according to claim 10 , wherein the band-pass filter is a cosine windowed-sinc filter generated based on an ideal low-pass filter and a window function.
12 . The method according to claim 11 , 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 ƒc 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.
13 . The method according to claim 11 , wherein the cosine windowed-sinc filter is an 8-tap filter, a 6-tap filter, or a 4-tap filter.
14 . The method according to claim 10 , 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.
15 . The method according to claim 14 , wherein the cost function is associated with the rounded filter coefficients and a reference.
16 . The method 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 method according to claim 14 , further comprising:
encoding the selected combination of rounded filter coefficients of the band-pass filter into at least one of Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), an Adaptation Parameter Set (APS), and a slice header.
18 . The method according to claim 10 , 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.
19 . A method of storing a bitstream, the method comprising:
in response to a target picture and a reference picture having different resolutions, obtaining a chroma Cr sample at a fractional sample position by applying a band-pass filter to the reference picture;
generating a bitstream comprising coded information associated with the chroma Cr sample; and
storing the bitstream in a non-transitory computer-readable medium,
wherein the applying of the band-pass filter performs a motion compensated interpolation with reference down-sampling on the reference picture, the band-pass filter having a kernel function based on a ratio between the resolutions of the target picture and the reference picture.
20 . The method according to claim 19 , wherein the band-pass filter is a cosine windowed-sinc filter generated based on an ideal low-pass filter and a window function.