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60 % lower than that of AVC in 69.4 % of the trials.
4
These results are consistent
with the subjective results reported in [
8
]. In addition, comparing the coding
efficiency gains of HEVC relative to AVC for certain 4K sequences in this study with
those gains reported in earlier studies (e.g., [
10
]), in which high-quality resampled
(lower-resolution) versions of the same video sequences were used, it can be seen
that the coding efficiency gains of HEVC relative to AVC are larger for the 4K
sequences.
5
This comparison suggests that the increased coding efficiency gains for
HEVC compared with AVC observed for 4K sequences cannot be explained solely
by differences in content.
9.6
Conclusions
In this chapter, performance analysis of HEVC in comparison with AVC in terms
of objective as well as subjective quality assessments are given. Because of the
increased flexibility offered by HEVC, methods to select the best coding parameters,
in a rate-distortion sense, are also described. Special care has been taken to apply
a unified approach when conducting subjective and objective quality evaluations
between HEVC and AVC. Both objective and subjective tests results indicate
significant gains in compression efficiency of HEVC over AVC. More specifically,
the bit rate reduction, based on objective evaluation of CTC test sequences, indicates
an overall performance improvement of about 22 % for AI, 43 % for RA, 37 % for
LDB and 35 % for LDP over AVC. Furthermore, by using non-CTC test sequences,
we observe up to 76 % improvement in coding efficiency, as indicated in Table
9.9
.
Results of subjective evaluation tests indicate that an even higher bit rate saving in
the ranges of 55-87 % can be achieved. The informal visual quality evaluation test
results also confirm that HEVC yields a substantial improvement in compression
capability beyond that of AVC for video streaming applications. It is also suggested
that the coding performance gains of HEVC over AVC generally increase with
increasing video resolution up to at least 4K resolutions.
Acknowledgments
Regarding Sect.
9.4
, the authors wish to thank 4EVER consortium, British
Broadcasting Corporation (BBC), Kamerawerk GmbH and Technicolor for providing the original
video test sequences used for visual testing. Our special thanks and gratitude go also to T. K. Tan,
of NTT Docomo, for his help and support in the preparation of coded video test sequences used for
subjective performance evaluations in Sect.
9.4
. Subjective evaluations performed at EPFL were
possible thanks to the Swiss National Foundation for Scientific Research (FN 200021-143696-1),
EC funded Network of Excellence VideoSense, and COST Action IC1003 European Network
on Quality of Experience in Multimedia Systems and Services QUALINET. Efforts by Hiromi
Nemoto for set up and conducting subjective evaluations at EPFL are also acknowledged.
4
The 69.4 % result was derived by summing the selection counts in the HEVC B, HEVC SB and
NP columns of Table
9.12
and dividing by the total number of selection counts.
5
The earlier studies also used earlier versions of the HEVC draft standard and a slightly different
evaluation methodology.
