title: Feature Detection in OpenCV Python Bindings
body: <p>I've combed the web looking for a way to get the OpenCV 2.3.1a feature extraction/descriptor bindings to spit out any flavor of image features/descriptors(STAR/SURF/ORB/SIFT/FAST). I am well aware that OpenCV has a method called "goodFeaturesToTrack. This doesn't help me as there are no feature descriptors (which is what I really need). I have followed the documentation as listed here:</p>
  
  <p><a href="http://opencv.itseez.com/modules/features2d/doc/feature_detection_and_description.html" rel="noreferrer">http://opencv.itseez.com/modules/features2d/doc/feature_detection_and_description.html</a></p>
  
  <p>Nothing seems to work. I've tried all of the flavors of descriptors/features. I've tried using single and multiple channel images (i.e. color and black and white) and multiple image formats (8bit and 32f). I have worked with the current distribution and building the bindings from the source repo. Most of the methods result in a "unknown is not a numpy array" error. Here is an example:</p>
  
  <pre><code>SimpleCV:1&gt;import cv2
  SimpleCV:2&gt;img = Image("aerospace.jpg")
  SimpleCV:3&gt;bwimg = img._getGrayscaleBitmap()
  SimpleCV:4&gt;bwimg
  SimpleCV:4&gt;&lt;iplimage(nChannels=1 width=600 height=400 widthStep=600 )&gt;
  SimpleCV:5&gt;surfer = cv2.SURF(0.5,4,2,False,False)
  SimpleCV:6&gt;points = surfer.detect(bwimg,None)
  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  
  /Library/Python/2.6/site-packages/SimpleCV-1.2-py2.6.egg/SimpleCV/Shell/Shell.pyc in &lt;module&gt;()
  -
  
  TypeError: &lt;unknown&gt; is not a numpy array
  SimpleCV:7&gt;
  </code></pre>
  
  <p>It is worth noting that I am using SimpleCV to load the image, but the method _getGrayscaleBitmap() returns the gray 8bit IPL image used by OpenCV. I am sure this works as I use it with hundred of other OpenCV methods without incidence. </p>
  
  <p>So can anyone point me to a <em>WORKING</em> example of this code on the web. I have combed through dozens of examples and found nothing that works. </p>