Graphics Reference
In-Depth Information
second part, an assessment of its throughput implications is performed. Finally, the
reduction in memory requirements is analyzed.
Simulations were performed under common test conditions set by the JCT-VC
[
6
,
101
] as well as corresponding settings for H.264/AVC JM [
30
]. Note that those
common conditions for the HEVC reference software HM [
35
] are intended to
reflect the typical bitstreams in applications of HEVC. During standardization of
HEVC, this configuration was also used to evaluate the coding efficiency impact of
proposals.
In [
6
], four different test cases labeled as
Intra
,
Random Access
,
Low Delay B
,
and
Low Delay P
are specified. The Intra test case specifies that all pictures are
coded as intra pictures. In the Random Access test case, intra pictures are inserted
in regular intervals of approximately 1.1 s in order to enable random access. As a
temporal coding structure, hierarchical B pictures with groups of eight pictures are
employed. Both the Low Delay B and Low Delay P test case specify that the pictures
are coded in display order, so that the resulting structural encoding-decoding delay is
suitable for low-delay communication applications. The latter two coding conditions
differ only in the used slice type. In the Low Delay B test case, B slices are used,
whereas only P slices are used in the Low Delay P test case. Note that in those low-
delay test cases only one intra picture is used at the beginning of each test sequence.
The same set of test sequences as in the standardization process of HEVC has
been used [
6
]. The test sequences are categorized into different classes, each with
a particular spatial resolution. As an exception, the class labeled as
Screen content
in the following represents a special class that contains test sequences with typical
screen and graphics content, but with varying spatial resolutions.
8.8.1
Coding Efficiency
Evaluation of coding efficiency for CABAC has been restricted to the syntax ele-
ments of transform coefficient coding. For that purpose, an extension of the residual
coding scheme, specified for CABAC in H.264/AVC [
46
], was implemented into the
HM to also cover residual coding of 16
16 and 32
32 TBs. This straightforward
extension was realized by increasing the number of successive scan positions
sharing the same context model for both SIG and LAST of those TBs. For the
remaining syntax elements related to transform coefficient level coding, the same
rules as defined for CABAC in H.264/AVC are applied [
46
].
Tab le
8.16
shows the so-called Bjøntegaard delta bit rate (BD-rate) for the
luma component [
5
] as a measure of the gain in coding efficiency obtained for
the transform coefficient level coding in HEVC relative to the aforementioned
straightforward CABAC extension. Overall performance gains of 3.4-4.8 % in terms
of averaged BD-rate savings can be attributed to the improved transform coefficient
coding techniques in HEVC. The largest improvements are achieved for the Intra
test case, which is mainly due to the relatively large energy of the corresponding
residual signals.
