Graphics Reference
In-Depth Information
filter_across_slices_enabled_flag
equal to 1 indicates that the in-
loop filters are applied across the left and upper boundaries of the current slice.
When the flag is equal to 0, in-loop filtering operations are not applied across the left
and upper boundaries of the current slice. When the flag is not present, it is inferred
to be equal to
pps_loop_filter_across_slices_enabled_flag
.
A picture parameters set (PPS) flag
loop_filter_across_tiles_
enabled_flag
equal to 1 specifies that in-loop filters are applied across tile
boundaries. When the flag is equal to 0, it specifies that in-loop filtering operations
are not performed across tile boundaries. When the flag is not present, the value of
loop_filter_across_tiles_enabled_flag
is inferred to be equal to 1.
These flags provide additional error resilience since an error created because of a
slice or tile loss will not propagate into neighboring slices or tiles of the same picture
(however, it may propagate to other slices or tiles of subsequent pictures because of
inter-picture prediction).
7.5
Coding Efficiency and Subjective Quality Improvements
The HEVC in-loop filters improve both the objective and subjective quality. The
objective quality improvement is achieved due to increasing the quality of the
reconstructed pictures. There is also an additional effect due to better quality of
reference pictures, which improves motion prediction and therefore the coding
efficiency.
In this section, the compression efficiency improvements have been evaluated on
the JCT-VC video sequences test set. The results are provided for several classes
of sequences and under different coding conditions defined in the HEVC common
test conditions document [
6
]. These configurations are: All Intra where only intra-
prediction is used; Random Access which uses intra pictures over certain time
intervals and hierarchical-B coding structure; and two low-delay configurations,
which have only one intra-picture, and where motion-compensated prediction uses
only temporally preceding pictures. The Low Delay P (LP) configuration does
not use bi-directional motion-compensated prediction. The BD-rate is used in the
HEVC standardization as a measure for the average bit rate reduction at the same
mean squared error [
5
]. The HEVC reference software HM11.0 was used in all
experiments. The reported decoding time has been evaluated by decoding the
bitstreams on a Windows 7 (64bit) PC with i7-920 CPU and 8GB of RAM without
writing the reconstructed pictures to the disk.
7.5.1
Deblocking Coding Efficiency and Subjective
Quality Improvements
The results for objective performance of the deblocking filter are provided in
Tab le
7.4
. The results show that applying HEVC deblocking leads to the 1.3-3.2 %
