Game Development Reference
In-Depth Information
Fig. 7.5
The relationship
between thresholds
ʱ
,
ʲ
and
QP
significant and boundary discontinuities are more likely artifacts. The filters with
a bigger strength could be applied. Therefore, the two thresholds should be large.
AVS-2 defines a look-up table to store the two thresholds. Their indices, denoted as
IndexA and IndexB, for the lookup table is derived by the Eqs. (
7.5
)-(
7.7
).
QP
av
=
(
QP
p
+
QP
q
+
1
)>>
1
,
(7.5)
IndexA
=
max
(
0
,
min
(
63
,
QP
av
+
AlphaOffset
)),
(7.6)
IndexB
=
max
(
0
,
min
(
63
,
QP
av
+
BetaOffset
)).
(7.7)
AlphaOffset
and
BetaOffset
are variables, which provide a picture-level adjustment
for users.
The
Boundary-Strength
for chroma components, denoted as
BS
c
, is derived
directly from the BS of luminance as follows:
BS
C
=
max
(
BS
−
1
,
0
) .
(7.8)
When
BS
value is 0, the deblocking filtering is skipped. The deblocking filter strength
in chroma components is weaker than that of luminance component because the
blocking artifacts are not obvious in chroma components.
Besides the filtering skipped when BS equals to 0, for P frames, all the filtering
boundaries in coding units are skipped when there are not quantized coefficients
in the coding unit and the motion vector difference between it and its neighboring
coding unit (left or upper neighbors) is smaller than one integer pixel, which also
share the same reference frame. This is because they are copied from the neighboring
blocks of the same reference frame, which has been filtered.
