Graphics Reference
In-Depth Information
Tabl e 3. 3
Coding efficiency improvement for successively enabling PUs of selected sizes. The
shown average bit-rate savings are measured relative to a configuration with 16
16 PUs only. In
all configurations, the transform coding is done using a 4
4 transform
Enabled PU sizes
Entertainment applications
Interactive applications
16 16 and 8 8 PUs
2:7 %
4:4 %
Square PUs from 4 4 to 16 16
6:1 %
5:6 %
Square PUs from 4 4 to 32 32
15:4 %
23:0 %
Square PUs from 4 4 to 64 64
18:7 %
30:3 %
All modes except asym. (
C
4
4 PUs)
20:0 %
31:0 %
All HEVC PU sizes (C
4
4 PUs)
20:7 %
33:0 %
Tabl e 3. 4
Coding efficiency improvement for successively increasing the maximum TU size. The
shown average bit-rate savings are measured relative to a configuration with 4
4 TUs only. In all
configurations, all supported CU and PU sizes are enabled and the minimum TU size is 4
4
Maximum enabled TU size
Entertainment applications
Interactive applications
Maximum TU size of 8
8
6:8 %
8:5 %
Maximum TU size of 16
16
11:9 %
14:7 %
Maximum TU size of 32
32
13:9 %
17:5 %
aspects of H.264
j
MPEG-4 AVC in the comparison, we enabled 4
4 PUs in
most of the configurations, even though they are not supported in the HEVC. This
small syntax modification does not change the interpretation of the results, since the
average bit-rate saving for additionally enabling 4
4 PUs in HEVC is typically less
than 0.1 % for high-resolution video [
22
].
The second experiment evaluates the impact of supporting different transform
sizes. Here, we enabled all CU and PU sizes supported in the HEVC standard, but
restricted the maximum TU size. In the reference configuration, only 4
4 TUs
were allowed, similar as in the Main profile of H.264
j
MPEG-4 AVC. While the
minimum TU size of 4
4 samples was held constant, the maximum TU size was
successively increased. The corresponding coding efficiency gains are summarized
in Table
3.4
. A significant gain of 6.8 % for the entertainment scenario and 8.5 %
for the interactive scenario is already obtained by additionally enabling 8
8 TUs, a
configuration which is conceptionally similar to the High profile of H.264
j
MPEG-4
AVC. The bit-rate saving relative to the configuration with 4
4 TUs only is further
increased to 13.9 % and 17.5 % for the entertainment and interactive application
scenarios, respectively, if all transform sizes supported in HEVC are enabled.
Besides the maximum and minimum TU sizes, also the maximum depth of the
residual quadtree (RQT) can be chosen by an encoder in HEVC. For investigating
its impact on coding efficiency, we enabled all transform sizes, but restricted the
maximum RQT depth. In the reference configuration, we set the maximum RQT
to the minimum supported value of 0. It should be noted that in this setting, as
already discussed above, the partitioning of a CU into multiple PUs implies also
the subdivision into four TUs. If the maximum RQT depth is set equal to 1, the
subdivision of a CU into four TUs can be selected by the encoder, unless the CU
