Graphics Reference
In-Depth Information
Tabl e 8. 2
Examples of different binarizations
Truncated
Truncated
Exp-Golomb
Fixed-Length
Unary (TrU)
Rice (TRk)
(EGk)
(FL)
N
Unary (U)
cMax
D
7
k
D
1;cMax
D
7
k
D
0
cMax
D
7
0
0
0
00
1
000
1
10
10
01
010
001
2
110
110
100
011
010
3
1110
1110
101
00100
011
4
11110
11110
1100
00101
100
5
111110
111110
1101
00110
101
6
1111110
1111110
1110
00111
110
7
11111110
1111111
1111
0001000
111
8.2.1
Binarization
The coding strategy of CABAC is based on the finding that a very efficient coding
of non-binary syntax element values in a hybrid block-based video coder, like
components of motion vector differences or transform coefficient level values, can
be achieved by employing a binarization scheme as a kind of preprocessing unit
for the subsequent stages of context modeling and arithmetic coding. In general,
a binarization scheme defines a unique mapping of syntax element values to
sequences of binary symbols, so-called bins, which can also be interpreted in terms
of a binary code tree. The design of binarization schemes in CABAC both for
H.264/AVC and HEVC is based on a few elementary prototypes whose structure
enables fast implementations and which are representatives of some suitable model-
probability distributions.
Several different binarization processes are used in HEVC including k-th
order truncated Rice (TRk), k-th order Exp-Golomb (EGk), and fixed-length (FL)
binarization. Parts of these forms of binarization, including the truncated unary
(TrU) scheme as the zero-order TRk binarization, were also used in H.264/AVC.
These various methods of binarization can be explained in terms of how they would
signal an unsigned value N . Examples are also provided in Table
8.2
.
Unary coding involves signaling a bin string of length N
C
1, where the first N
bins are 1 and the last bin is 0. The decoder searches for a 0 to determine when
the syntax element is complete. For the TrU scheme, truncation is invoked for
the largest possible value cMax
1
of the syntax element being decoded.
k-th order truncated Rice is a parameterized Rice code that is composed of a
prefix and a suffix. The prefix is a truncated unary string of value N>>k,
where the largest possible value is cMax. The suffix is a fixed length binary
representation of the least significant bins of N ; k indicates the number of least
1
cMax is defined by the standard for each relevant type of syntax element.
