Databases Reference
In-Depth Information
T A B L E 16 . 3
Context determination for the zero-coding
mode.
LL & LH
HL
HH
Context
σ
h
σ
v
σ
d
σ
h
σ
v
σ
d
σ
d
σ
h
+
v
0
0
0
0
0
0
0
0 0
0
0
1
0
0
1
0
1 1
0
0
20 0
20
2 2
0
1
x
1
0
x
1
0 3
0
2
x
2
0
x
1
1 4
1
0
0
0
1
0
1
2 5
1
0
10 1
12 0 6
1
1x
11x 2
1 1
2
x
x
x
2
x
3x 1
T A B L E 16 . 4
Prediction and context generation for the
sign coding process.
s
h
s
v
Context
Prediction
1
1
SC4
1
1
0
SC3
1
1
−
1
SC2
1
0
1
SC1
1
0
0
SC0
1
0
−
1
SC1
−
1
−
1
1
SC2
−
1
−
1
0
SC3
−
1
−
1
−
1
−
1
SC4
horizontal or
v
for vertical) according to the following rule:
⎧
⎨
1
if both neighbors are positive or one is positive and one unknown
s
x
=
−
1
if both neighbors are negative or one is negative and one unknown
⎩
0
otherwise
These values are then used according to the rule in Table
16.4
to generate both the context
for the arithmetic coder and the prediction for the sign. If the prediction is accurate, the encoder
encodes a 0 in the appropriate sign coding context, otherwise it encodes a 1. Note that in this
pass coefficients that have previously been declared significant are not encoded.
In the magnitude refinement pass, the bits corresponding to coefficients that have been
declared significant in previous passes are encoded using the contexts MR0, MR1, and MR2.
The context MR0 is used when the magnitude refinement pass is applied to a coefficient for
the first time, and there are no horizontal or vertical neighbors that are significant. If there
are significant neighbors and the magnitude refinement pass is being applied to the coefficient
for the first time, the context MR1 is used. Finally, if this is not the first time the magnitude
refinement is being applied to a coefficient, the context MR2 is used.
