Graphics Reference
In-Depth Information
Start Transform Block
Scan order based on Intra/Inter, intra
prediction mode, TB size, luma/
chroma [Tab. 8.8, Fig. 8.16]
Select Diagonal, Vertical,
Horizontal Scan
Truncated Unary binarization ( cMax
based on TB size), and bypass coded
[Tab. 8.9 & 8.10]
Last Position X, Y
( last_sig_coeff_x_prefix,
last_sig_coeff_y_prefix )
Fixed Length binarization, and context
based on TB size, luma/chroma, bin
Index [Tab. 8.9]
Last Position X, Y
( last_sig_coeff_x_suffix,
last_sig_coeff_y_suffix )
Inferred for DC or last position.
Otherwise, context depends on 4x4
neighbors (bottom and right) and
luma/chroma [Fig. 8.17]
Coded Sub Block Flag
( coded_sub_block_flag )
If last 4x4, repeat <16x
Otherwise, re p eat 16x
Inferred for last position or if all other
sig_coeff_flag non-zero in 4x4
subblock. Otherwise, context depends
on 4x4 neighbors (bottom and right),
luma/chroma, scan, position within
TB, and position within 4x4 subblock
[Tab. 8.11]
Repeat for number of
4x4 subblocks based
on last position
Significant coefficient flag
( sig_coeff_flag )
Coefficient Level and Sign Coding
(see Fig. 8.25)
End Transform Block
Fig. 8.21
Flow chart for coding the syntax elements of a TB in HEVC
the subblock. Note that context 0 is used to code the sig_coeff_flag of the DC
position of all luma TBs, and context 27 is used for the DC position of all chroma
TBs.
8.6.5
Absolute Coefficient Level and Coefficient Sign
In HEVC, parsing of transform coefficient level information is performed subblock-
by-subblock using up to five scan passes for each subblock. The first scan pass is
devoted to the SIG flags, as already explained in Sects. 8.6.4.1 and 8.6.4.3 .Inthe
second and third pass, the two additional flags coeff_abs_level_greater1
_flag (ALG1) and coeff_abs_level_greater2_flag (ALG2) are con-
ditionally parsed, indicating for each relevant scan position if the corresponding
absolute value of the coefficient level, i.e., the absolute level (AL) is greater than 1
and 2, respectively. However, only up to 8 ALG1 flags and one ALG2 flag are
transmitted for each subblock, as will be explained in more detail below. In the third
scan pass, the sign of each significant level is signaled with the possible exception
 
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