 argument a third
row containint the descriptor norm, or engergy, before
contrast normalization. This information can be used to
suppress low contrast descriptors.
</p></dd><dt>
Fast
</dt><dd><p>
If specified, use a piecewise-flat, rather than Gaussian,
windowing function. While this breaks exact SIFT equivalence,
in practice is much faster to compute.
</p></dd><dt>
FloatDescriptors
</dt><dd><p>
If specified, the descriptor are returned in floating point
rather than integer format.
</p></dd><dt>
Geomerty
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