Graphics Reference
In-Depth Information
8.3.3.2
Group Bypass Coded Bins
Multiple bypass bins can be processed in the same cycle only if they occur
consecutively
within the bitstream. Thus, bins should be reordered such that bypass
coded bins are grouped together in order to increase the likelihood that multiple bins
are processed per cycle [
19
,
67
,
87
].
8.3.3.3
Group Bins with Same Context
Processing multiple regular coded bins in the same cycle often requires specula-
tive calculations for context modeling. The amount of speculative computations
increases if bins using different contexts and context modeling logic are interleaved,
since numerous combinations and permutations must be accounted for. Thus, to
reduce speculative computations, bins should be reordered such that bins with the
same contexts and context modeling logic are grouped together so that they are
likely to be processed in the same cycle [
9
,
10
,
73
]. This also reduces context
switching resulting in fewer memory accesses, which also increases throughput
and reduces power consumption. This technique was first introduced in [
10
]and
was referred to as parallel context processing (PCP) throughout the standardization
process.
8.3.3.4
Reduce Context Modeling Dependencies
Speculative computations are required for multiple bins per cycle decoding due to
the dependencies in the context modeling. For instance, this is an issue when the
context modeling for the next bin depends on the decoded value of the current bin.
Reducing these dependencies simplifies the context modeling logic and reduces the
amount of speculative calculations required to process multiple bins in parallel [
18
,
80
,
85
].
8.3.3.5
Reduce Total Number of Bins
In addition to increasing the throughput, it is desirable to reduce the workload itself
by reducing the total number of bins that need to be processed. This can be achieved
by changing the binarization, inferring the value of some bins,
5
and sending higher
level flags to avoid signaling redundant bins [
12
,
56
,
59
].
5
The benefit of inferring bins must be traded-off with a potential increase in context selection
complexity.
