Databases Reference
In-Depth Information
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F I GU R E 16 . 20
The third most significant bitplane of the example stripe of
coefficients in Figure
16.16
. The coefficients declared significant
are in bold boxes.
As we begin encoding the next bitplane the significance status of the various coefficients is
as shown in Figure
16.20
. As we can see, the number of significant coefficients has increased.
This means that this bitplane will be encoded in the zero-coding mode with no opportunity to
use the more parsimonious run-length coding mode. This is in line with other algorithms that
generate an embedded bitstream. Much of the coding resources are devoted to the last bits of
precision.
The example also illustrates another feature of JPEG 2000, namely the existence of a large
number of truncation points. The end of each pass in the encoding presents the opportunity
for truncating the bitstream at that point. This permits the natural construction of fractional
bitplanes. This is done as part of the Tier II coding procedures.
16.5.6 Tier II Coding
Tier II coding in JPEG 2000 is focused on the rich scalability options characteristic of this
standard. We defer much of the discussion of the organization of the data to Section
16.5.7
.In
this section we look at how the JPEG 2000 standard takes advantage of the truncation points
described in the previous section. The PCRD algorithm makes use of this particular feature in
building the quality levels that provide JPEG 2000 with its SNR scalability.
