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gwlucastrig committed Nov 26, 2024
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2 changes: 1 addition & 1 deletion docs/notes/EntropyMetricForDataCompression.html
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Expand Up @@ -332,7 +332,7 @@ <h2>Beyond entropy-based compression: the Deflate algorithm</h2>

<figure>
<img border=0 width=496 height=305 src="EntropyMetricForDataCompression_files/image016.png">
<figcaption>Figure 3 &ndash; First-order entropy versus Deflate bits-per-symbol rates for SRTM data (data source: NASA, 2020)).</figcaption>
<figcaption>Figure 3 &ndash; First-order entropy versus Deflate bits-per-symbol for SRTM data (data source: NASA, 2020).</figcaption>
</figure>


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6 changes: 3 additions & 3 deletions docs/notes/EntropyMetricForDataCompressionCaseStudies.html
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Expand Up @@ -108,8 +108,8 @@ <h2>Data compression</h2>
a lot of the content of the source file could easily be accomodated by two-byte (short) integers rather
than the four-bytes used by the source data. It is unclear why the original authors elected to
store their data as four-byte integers when they could have used two-byte integers.
But we do know a lot of the byte concent of the source data is just filler (either 0x00 if the
elevation value is positive, or 0xff if the elevation is negative).</p>
But we do know that a lot of the byte content of the source data is just filler
(either 0x00 if the elevation value is positive, or 0xff if the elevation is negative).</p>

<p>The entropy rate computation is driven by unpredictability in a data set.
And, because the filler bytes are highly predictable, they tend to reduce
Expand Down Expand Up @@ -181,7 +181,7 @@ <h2>Statistical variation over the domain of a data set</h2>
<p>The entropy rates in the figure are based on the local statistics at the area represented by each pixel.
They run from 0 to 9.7 bits/elevation. When we compute entropy for the entire data set,
it combines data from much different areas (flat plains, to high mountain ranges, to deep ocean trenches).
So the overall computed entropy is 12.9 bits/elevation value.</p>
So the overall computed entropy is 12.89 bits/elevation value.</p>

<p>Data compression techniques use the statistical properties of source data (entropy and others)
to develop a compact form for their output. The figure above illustrates the fact that
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