ROUNDING IN PAIRWISE AVERAGE CANDIDATE CALCULATIONS
Devices, systems and methods for unified rounding in sub-block based prediction are described. In a representative aspect, a method of video processing includes generating, for a processing of a current block of video, a pairwise merge candidate based on a pair of motion candidates, and performing, based on the pairwise merge candidate, a conversion between the current block and a bitstream representation of the video. In another representative aspect, a method of video processing includes generating, for a current block of video coded using a geometry partition mode, a uni-prediction motion candidate based on a scaled motion vector and a List0 motion vector, and performing, based on the uni-prediction motion candidate, a conversion between the current block and a bitstream representation of the video.
1 . A method of coding video data, comprising:
constructing, for a current block of a video, a merge motion candidate list which comprises at least two merge motion candidates;
deriving, based on a position index to the merge motion candidate list, a pairwise average merging candidate from a pair of merge motion candidates included in the merge motion candidate list; and
performing, based on the pairwise average merging candidate, a conversion between the current block and a bitstream of the video,
wherein the pair of merge motion candidates comprises a first motion vector MV0=(MV0x, MV0y) of a reference picture list L in a first merge motion candidate and a second motion vector MV1=(MV1x, MV1y) of the reference picture list L in a second merge motion candidate, and wherein MV*=(MV*x, MV*y) is the pairwise merge candidate such that:
MV*x =SignShift( MV 0 x+MV 1 x ,1) and MV*y =SignShift( MV 0 y+MV 1 y, 1),
wherein
SignShift
(
x
,
s
)
=
{
(
x
+
off
)
s
x
≥
0
-
(
(
-
x
+
off
)
s
)
x
<
0
,
wherein off and s are integers, and wherein » represents a right shift operation.
2 . The method of claim 1 , wherein the position indices of the pair of merge motion candidates are 0 and 1.
3 . The method of claim 1 , wherein the reference picture list L comprises reference picture list 0 (L0) or reference picture list 1 (L1).
4 . The method of claim 1 , further comprising:
inserting the pairwise average merging candidate into the merge motion candidate list.
5 . The method of claim 1 , wherein off=0.
6 . The method of claim 1 , wherein off=0 upon a determination that s=0.
7 . The method of claim 1 , wherein off=1«(s−1).
8 . The method of claim 1 , wherein off=1«(s−1) upon a determination that s≠0.
9 . The method of claim 1 , wherein off=(1«(s−1))−1.
10 . The method of claim 1 , wherein the conversion comprises encoding the current block into the bitstream.
11 . The method of claim 1 , wherein the conversion comprises decoding the current block from the bitstream.
12 . An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
construct, for a current block of a video, a merge motion candidate list which comprises at least two merge motion candidates;
derive, based on a position index to the merge motion candidate list, a pairwise average merging candidate from a pair of merge motion candidates included in the merge motion candidate list; and
perform, based on the pairwise average merging candidate, a conversion between the current block and a bitstream of the video,
wherein the pair of merge motion candidates comprises a first motion vector MV0=(MV0x, MV0y) of a reference picture list L in a first merge motion candidate and a second motion vector MV1=(MV1x, MV1y) of the reference picture list L in a second merge motion candidate, and wherein MV*=(MV*x, MV*y) is the pairwise merge candidate such that:
MV*x =SignShift( MV 0 x+MV 1 x, 1) and MV*y =SignShift( MV 0 y+MV 1 y, 1),
wherein
SignShift
(
x
,
s
)
=
{
(
x
+
off
)
s
x
≥
0
-
(
(
-
x
+
off
)
s
)
x
<
0
,
wherein off and s are integers, and wherein » represents a right shift operation.
13 . The apparatus of claim 12 , wherein the position indices of the pair of merge motion candidates are 0 and 1.
14 . The apparatus of claim 12 , further comprising:
inserting the pairwise average merging candidate into the merge motion candidate list.
15 . The apparatus of claim 12 , wherein off=0.
16 . The apparatus of claim 12 , wherein off=1«(s−1).
17 . The apparatus of claim 12 , wherein off=1«(s−1) upon a determination that s≠0.
18 . The apparatus of claim 1 , wherein off=(1«(s−1))−1.
19 . A non-transitory computer-readable storage medium storing instructions that cause a processor to:
construct, for a current block of a video, a merge motion candidate list which comprises at least two merge motion candidates;
derive, based on a position index to the merge motion candidate list, a pairwise average merging candidate from a pair of merge motion candidates included in the merge motion candidate list; and
perform, based on the pairwise average merging candidate, a conversion between the current block and a bitstream of the video,
wherein the pair of merge motion candidates comprises a first motion vector MV0=(MV0x, MV0y) of a reference picture list L in a first merge motion candidate and a second motion vector MV1=(MV1x, MV1y) of the reference picture list L in a second merge motion candidate, and wherein MV*=(MV*x, MV*y) is the pairwise merge candidate such that:
MV*x =SignShift( MV 0 x+MV 1 x ,1) and MV*y =SignShift( MV 0 y+MV 1 y, 1),
wherein
SignShift
(
x
,
s
)
=
{
(
x
+
off
)
s
x
≥
0
-
(
(
-
x
+
off
)
s
)
x
<
0
,
wherein off and s are integers, and wherein » represents a right shift operation.
20 . A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:
constructing, for a current block of the video, a merge motion candidate list which comprises at least two merge motion candidates;
deriving, based on a position index to the merge motion candidate list, a pairwise average merging candidate from a pair of merge motion candidates included in the merge motion candidate list; and
generating, based on the pairwise average merging candidate, the bitstream of the video;
wherein the pair of merge motion candidates comprises a first motion vector MV0=(MV0x, MV0y) of a reference picture list L in a first merge motion candidate and a second motion vector MV1=(MV1x, MV1y) of the reference picture list L in a second merge motion candidate, and wherein MV*=(MV*x, MV*y) is the pairwise merge candidate such that:
MV*x =SignShift( MV 0×+ MV 1×,1) and MV*y =SignShift( MV 0 y+MV 1 y, 1),
wherein
SignShift
(
x
,
s
)
=
{
(
x
+
off
)
s
x
≥
0
-
(
(
-
x
+
off
)
s
)
x
<
0
,
wherein off and s are integers, and wherein » represents a right shift operation.