Graphics Reference
In-Depth Information
The HEVC deblocking has two filtering modes: a normal filtering mode and a
strong filtering mode. A decision between these two modes is done for each four-
sample segment of a block boundary. The strong filtering is applied to the block
boundary if all of the following conditions are true for lines
i
D
0and
i
D
3(see
Fig.
7.6
)[
32
,
37
,
43
].
j
p
2;i
2p
1;i
C
p
0;i
j C j
q
2;i
2q
1;i
C
q
0;i
j
< “=8;
(7.2)
j
p
3;i
p
0;i
j C j
q
0;i
q
3;i
j
< “=8;
(7.3)
j
p
0;i
q
0;i
j
<2:5t
C
:
(7.4)
If all of the (
7.2
)-(
7.4
) are true, the strong filtering is applied, otherwise, the
normal deblocking filter is applied. The threshold parameter
t
C
is the clipping
parameter described later in this section. Equation (
7.4
) makes sure that the step
between the sample values at the sides of the block boundary is small, while (
7.2
)
checks that there are no significant signal variations at the sides of the boundary,
and (
7.3
) verifies that the signal on both sides is flat.
The deblocking filtering decisions for a block boundary including the decisions
between the strong and the normal filtering are summarized in a flowchart in
Fig.
7.7
.
7.2.2.2
Normal Filtering Mode
When a normal deblocking filtering mode is used, the following conditions are eval-
uated to decide how many samples are modified at each side of the block boundary.
Condition in (
7.5
) determines how many samples from the block boundary are
modified in block P, while condition in (
7.6
) determines how many samples are
modified in block Q (see Fig.
7.6
)[
36
]. The decisions use the same principle as
decision (
7.1
). The smoother the signal on the side of the block boundary, the more
filtering is applied [
35
].
j
p
2;0
2p
1;0
C
p
0;0
j
C
j
p
2;3
2p
1;3
C
p
0;3
j
<3=16“;
(7.5)
j
q
2;0
2q
1;0
C
q
0;0
j C j
q
2;3
2q
1;3
C
q
0;3
j
<3=16 “:
(7.6)
If (
7.5
) is true, two samples from the block boundary are modified in block P,
otherwise, one sample is modified. If (
7.6
) is true, two samples from the block
boundary are modified in block Q, otherwise, one sample is modified. The decisions
are made for each side of the block boundary independently, i.e. one sample may be
filtered on one side of the block boundary, and two samples on the other side.
When condition in (
7.1
) is true for a four-sample segment of the block boundary,
the deblocking filtering operations are subsequently applied to each of the four lines
