Method and apparatus of interpolation filtering for predictive coding
The present disclosure relates to intra- or inter-prediction for video encoding and decoding. For that purpose, an apparatus and methods obtain a reference sample and a subpixel offset value. A 4-tap interpolation filter is used to filter the reference sample to obtain a predicted sample value. The filter coefficients c 0 , c 1 , c 2 , and c 3 of the 4-tap interpolation filter satisfy c 0 = 16 - p 2 , c 1 = 16 + 16 - p 2 , c 2 = 16 + p 2 , and c 3 = p 2 , with p being a fractional part of the value of the subpixel offset.
1. A method for intra-prediction or inter-prediction processing of a video frame, comprising:
obtaining a reference sample;
obtaining a value of a subpixel offset; and
filtering, using a 4-tap interpolation filter, the reference sample to obtain a predicted sample value, wherein filter coefficients of the 4-tap interpolation filter are defined in a table as follows:
p
c 0
c 1
c 2
c 3
0
16
32
16
0
1
16
32
16
0
2
15
31
17
1
3
15
31
17
1
4
14
30
18
2
5
14
30
18
2
6
13
29
19
3
7
13
29
19
3
8
12
28
20
4
9
12
28
20
4
10
11
27
21
5
11
11
27
21
5
12
10
26
22
6
13
10
26
22
6
14
9
25
23
7
15
9
25
23
7
16
8
24
24
8
17
8
24
24
8
18
7
23
25
9
19
7
23
25
9
20
6
22
26
10
21
6
22
26
10
22
5
21
27
11
23
5
21
27
11
24
4
20
28
12
25
4
20
28
12
26
3
19
29
13
27
3
19
29
13
28
2
18
30
14
29
2
18
30
14
30
1
17
31
15
31
1
17
31
15
wherein p is a fractional part of the value of the subpixel offset, and c 0 , c 1 , c 2 , and c 3 are the filter coefficients of the 4-tap interpolation filter.
2. The method according to claim 1 , wherein a bit of p is set to zero.
3. The method according to claim 1 , wherein p is incremented by 1 and afterwards a lower bit of the incremented p is set to zero prior to using p to obtain the filter coefficients.
4. The method according to claim 1 , wherein the filter coefficients are calculated according to
c
0
=
1
6
-
p
2
c
1
=
1
6
+
c
0
c
2
=
c
0
+
p
c
3
=
c
0
-
p
.
5. An apparatus for intra-prediction or inter-prediction processing of a video frame, including:
a reference sample obtaining unit configured to obtain a reference sample;
a subpixel offset value obtaining unit configured to obtain a value of a subpixel offset; and
a 4-tap interpolation filter configured to filter the reference sample to obtain a predicted sample value, wherein filter coefficients of the 4-tap interpolation filter are defined in a table as follows:
p
c 0
c 1
c 2
c 3
0
16
32
16
0
1
16
32
16
0
2
15
31
17
1
3
15
31
17
1
4
14
30
18
2
5
14
30
18
2
6
13
29
19
3
7
13
29
19
3
8
12
28
20
4
9
12
28
20
4
10
11
27
21
5
11
11
27
21
5
12
10
26
22
6
13
10
26
22
6
14
9
25
23
7
15
9
25
23
7
16
8
24
24
8
17
8
24
24
8
18
7
23
25
9
19
7
23
25
9
20
6
22
26
10
21
6
22
26
10
22
5
21
27
11
23
5
21
27
11
24
4
20
28
12
25
4
20
28
12
26
3
19
29
13
27
3
19
29
13
28
2
18
30
14
29
2
18
30
14
30
1
17
31
15
31
1
17
31
15
wherein p is a fractional part of the value of the subpixel offset, and c 0 , c 1 , c 2 , and c 3 are the filter coefficients of the 4-tap interpolation filter.
6. The apparatus according to claim 5 , wherein a bit of p is set to zero.
7. The apparatus according to claim 5 , wherein p is incremented by 1 and afterwards a lower bit of the incremented p is set to zero prior to using p to obtain the filter coefficients.
8. The apparatus according to claim 5 , wherein the filter coefficients are calculated according to
c
0
=
1
6
-
p
2
c
1
=
1
6
+
c
0
c
2
=
c
0
+
p
c
3
=
c
0
-
p
.
9. A non-transitory computer-readable storage medium storing computer-executable instructions that, when executed by a processor, cause an apparatus to:
obtain a reference sample;
obtain a value of a subpixel offset; and
filter, using a 4-tap interpolation filter, the reference sample to obtain a predicted sample value, wherein filter coefficients of the 4-tap interpolation filter are defined in a table as follows:
p
c 0
c 1
c 2
c 3
0
16
32
16
0
1
16
32
16
0
2
15
31
17
1
3
15
31
17
1
4
14
30
18
2
5
14
30
18
2
6
13
29
19
3
7
13
29
19
3
8
12
28
20
4
9
12
28
20
4
10
11
27
21
5
11
11
27
21
5
12
10
26
22
6
13
10
26
22
6
14
9
25
23
7
15
9
25
23
7
16
8
24
24
8
17
8
24
24
8
18
7
23
25
9
19
7
23
25
9
20
6
22
26
10
21
6
22
26
10
22
5
21
27
11
23
5
21
27
11
24
4
20
28
12
25
4
20
28
12
26
3
19
29
13
27
3
19
29
13
28
2
18
30
14
29
2
18
30
14
30
1
17
31
15
31
1
17
31
15
wherein p is a fractional part of the value of the subpixel offset, and c 0 , c 1 , c 2 , and c 3 are the filter coefficients of the 4-tap interpolation filter.
10. The non-transitory computer-readable storage medium according to claim 9 , wherein a bit of p is set to zero.
11. The non-transitory computer-readable storage medium according to claim 9 , wherein p is incremented by 1 and afterwards a lower bit of the incremented p is set to zero prior to using p to obtain the filter coefficients.
12. The non-transitory computer-readable storage medium according to claim 9 , wherein the filter coefficients are calculated according to
c
0
=
1
6
-
p
2
c
1
=
1
6
+
c
0
c
2
=
c
0
+
p
c
3
=
c
0
-
p
.