Databases Reference
In-Depth Information
0
0
0
0
0
0
0
0
0
1
0
0 1
1
0
0
00
0
01
0
0
0
00
0
10
0
1
1
000
0
F I GU R E 16 . 19
The second most significant bitplane of the example stripe of
coefficients in Figure 15.16 after the significance propagation
pass. The encoded bits are shown in bold in shaded boxes.
encoded as a 0 in the ZC6 context. The second coefficient becomes significant in this bitplane
with
σ
h
=
1
,σ
v
=
0, and
σ
d
=
2. We encode a 1 in the ZC6 context and compute
s
h
=−
1 and
s
v
=
0, which implies a sign context of SC3. The predicted sign is negative, which is incorrect,
so we encode a 1 in the SC3 context. The next bit in this column is 0 with
σ
h
=
,σ
v
=
1
1, and
σ
d
=
1, so we encode a 0 in the ZC1 context. The final coefficient to be encoded in this pass
is the fourth coefficient in this column. This coefficient becomes significant in this bitplane
with
σ
h
=
1
,σ
v
=
0, and
σ
d
=
1. We encode a 1 in context ZC6. For this coefficient,
s
h
=
1
and
s
0. The predicted sign according to Table
16.4
is positive, so we encode a 0 in sign
context SC3. There are no other coefficients in this bitplane that have significant neighbors so
this concludes the significance propagation pass.
The bitplane at this point can be represented by Figure
16.19
where the bits that have been
encoded are shown in bold in shaded boxes. The bits in the darker boxes belong to coefficients
that were declared significant in the previous pass. These are the bits that are encoded in the
magnitude refinement pass. For each of these coefficients, the magnitude refinement pass is
being used for the first time; each of these coefficients have one or more significant neighbors,
so we encode each bit using the MR1 context. We encode a 0 in the MR1 context, a 0 in the
MR1 context, a 1 in the MR1 context, and a 1 in the MR1 context.
Finally, we use the cleanup pass to encode the remaining bits. The bits in the first column
all have significant neighbors, so they are encoded using the zero-coding contexts. The same
is true for the last bit in the second column and all of the bits in the sixth column. The bits
in the seventh column are all 0; they do not have any significant neighbors, so we encode this
column with a 0 in the run-length context. The eighth and ninth columns are also encoded
using a 0 in the run-length context. This brings to an end the coding of this bitplane.
v
=
