Graphics Reference
In-Depth Information
Fig. 7.11
Dependency of t
C
on QP. Reproduced with
permission from [
37
], © 2012
IEEE
25
20
15
10
5
0
0
10
20
30
40
50
60
QP
b
4
b
5
b
7
b
8
Hier. level 3
B
3
B
6
Hier. level 2
B
2
Hier. level 1
Hier. level 0
I
0
P
1
Fig. 7.12
Hierarchical-B coding structure with GOP8 illustrating different depth of the picture in
the coding structure [
38
]
efficiency by applying the base QP to the intra-coded pictures, QP
C
1totheB-
pictures at hierarchy level 0 (e.g. picture P
1
), QP
C
2 to the pictures at hierarchy
level 1. Hierarchy level 2 uses QP
C
3 and non-reference b-pictures at level 3 use
QP
C
4. The improvement in compression efficiency is achieved by coding with
better quality the pictures at lower hierarchical levels, which are used for prediction
of the pictures at higher hierarchy levels. However, in video sequences with chaotic
motion, e.g. showing water, smoke, fire, rain, or snow, the QP cascading may cause
block artifacts in the pictures at higher hierarchy levels, which is related to using
lower bit budget for those pictures because of higher QP values and coarser mode
decisions.
When the encoder uses hierarchical coding structure and QP cascading, the
deblocking parameters
tc_offset_div2
and
beta_offset_div2
can be
used to increase the deblocking strength for the pictures at higher hierarchy levels,
which improves the subjective quality on sequences with chaotic motion, while
