Graphics Reference
In-Depth Information
900
−
1
0
1
5
6
Zig-zag Scan
(forward for significance
map, reverse for coefficient
level & sign)
−
60 0 0
3100
2 4 7 12
3 8 11 13
9 10 14 15
0000
1 0 1 1 0 0 1 0 1
significant_coeff_flag
0
0
0
0
1
last_significant_coeff_flag
8
5
2
0
0
coeff_abs_level_minus1
0
1
0
1
0
coeff_sign_flag
Signaling order
1
0
0 1
0
1
0
0 0 0 1
0
0 1
1
1
0
0
0
1
2
0
5
1
8
0
Significance map
Coefficient level and sign
Fig. 8.8
4 transform block
in H.264/AVC. Note, however, that the corresponding bins for signaling of the absolute level (in
yellow
) are not explicitly shown
Example of CABAC-based transform coefficient coding for a 4
variety of transform block partitioning relative to H.264/AVC provides significant
coding gains, it also has implications in terms of implementation costs, both in terms
of memory bandwidth and computational complexity. To address this issue, HEVC
allows to restrict the RQT-based transform block partitioning by four parameters,
signaled by corresponding syntax elements in the SPS: the maximum and minimum
allowed transform block size (in terms of block width) n
max
and n
min
, respectively,
and the maximum depth of the RQT d
max
, with the latter given both individually
for intra-picture and inter-picture prediction. Note, however, that there is a rather
involved interdependency between these parameters (and other syntax elements),
such that, for instance, implicit subdivisions or implicit leaf nodes of the RQT may
occur. For more details, please refer to Chap.
3
.
The signaling of the transform block structure for each CU is similar to that of
the coding block structure at the CTU level. For each node of the RQT, a flag called
split_transform_flag
is signaled to indicate whether a given transform
block should be further subdivided into four smaller TBs. Context modeling for
the coding of this flag involves three different contexts with its related context
increment equal to 5
log
2
.TrafoSize/, where TrafoSize denotes the block width
of the corresponding luma transform block at the given RQT depth. Note that for
the choice of a luma CTB size of 64, n
max
D
32, n
min
D
4,andd
max
D
4,an
implicit leaf node is implied for the case of TrafoSize
D
4, whereas an implicit
