Graphics Reference
In-Depth Information
Fig. 8.18 Neighboring
CSBFs (right, bottom) used
for SIG context selection
CSBF right
CSBF bottom
a
b
c
d
2
1
1
0
2
2
2
2
2
1
0
0
2
2
2
2
1
1
0
0
1
1
1
1
2
1
0
0
2
2
2
2
1
0
0
0
0
0
0
0
2
1
0
0
2
2
2
2
0
0
0
0
0
0
0
0
2
1
0
0
2
2
2
2
Fig. 8.19
4 position based mapping for SIG context selection based on CSBF of neighboring
subblocks. ( a ) Pattern 1, ( b ) pattern 2, ( c ) pattern 3 and ( d ) pattern 4
4
scheme, the CSBF of the neighboring right and bottom subblocks (CSBF right ,
CSBF bottom ) are used to select one of four patterns shown in Fig. 8.19 : (0,0) maps
to pattern 1, (1,0) to pattern 2, (0,1) to pattern 3 and (1,1) to pattern 4. The pattern
maps each position within the 4 4 subblock to one of three contexts. As a result,
there are no intrinsic dependencies for context selection of SIG within each 4 4
subblock.
Reverse diagonal scanning order is used within the subblocks and for the
processing order of the subblocks themselves, as shown in Fig. 8.20 [ 76 ]. Both
significance map and coefficient levels are processed in this order. As an exception
to this rule, for 4 4 and 8 8 TBs to which MDCS is applied, reverse vertical
and horizontal scanning orders are used within the subblocks as well as for the
processing order of the subblocks themselves. Furthermore, as shown in Table 8.11 ,
different sets of contexts for coding of SIG are used for diagonal and non-diagonal
(vertical and horizontal) scans in both 4 4 luma and chroma TBs, and 8 8 luma
TBs [ 77 ].
8.6.4.4
Summary of Significance Map Coding in HEVC
Figure 8.21 summarize the steps required to code the significance map. This process
is repeated for every non-zero TB in HEVC. Table 8.11 summarizes the multiple
steps of classification used to assign the 42 contexts of sig_coeff_flag .
Contexts 0 to 26 are used for luma coded TBs, while 27 to 41 used for chroma TBs.
The contexts are further mapped based on the TB size, the scan direction, whether
the subblock is DC or non-DC, CSBF of neighboring subblocks, and position within
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