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Here is a patent that looks like SIFT. Full text and images<br>
are available from <a class="moz-txt-link-abbreviated" href="http://www.uspto.gov">www.uspto.gov</a> .<br>
<br>
(The search string is for Inventor contains "Lowe" and<br>
Assignee contains "Columbia",as in Univ.of...)<br>
<br>
--Rik<br>
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<p><b><font face="Times New Roman">United States Patent</font></b> <b>
<font face="Times New Roman">6,711,293</font></b> <br>
<b><i><font face="Times New Roman">Lowe</font></i><font
face="Times New Roman"></font></b> <b> <font face="Times New Roman">March
23, 2004</font></b> <br>
<br>
<font size="4" face="Times New Roman">Method and apparatus for
identifying scale invariant features in an image and use of same for
locating an object in an image</font><br>
</p>
<p align="center"><b><font face="Times New Roman">Abstract</font></b></p>
<p><font face="Times New Roman">A method and apparatus for identifying
scale invariant features in an image and a further method and apparatus
for using such scale invariant features to locate an object in an image
are disclosed. The method and apparatus for identifying scale invariant
features may involve the use of a processor circuit for producing a
plurality of component subregion descriptors for each subregion of a
pixel region about pixel amplitude extrema in a plurality of difference
images produced from the image. This may involve producing a plurality
of difference images by blurring an initial image to produce a blurred
image and by subtracting the blurred image from the initial image to
produce the difference image. For each difference image, pixel
amplitude extrema are located and a corresponding pixel region is
defined about each pixel amplitude extremum. Each pixel region is
divided into subregions and a plurality of component subregion
descriptors are produced for each subregion. These component subregion
descriptors are correlated with component subregion descriptors of an
image under consideration and an object is indicated as being detected
when a sufficient number of component subregion descriptors (scale
invariant features) define an aggregate correlation exceeding a
threshold correlation with component subregion descriptors (scale
invariant features) associated with the object. </font></p>
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