title: how to correctly use peopledetect.py in opencv?
body: <p>I'm newbie of opencv and I have real need for detecting people/human within some images,   I find python interface named peopledetect.py and I look through code just like this..</p>
  
  <pre><code>#!/usr/bin/env python
  
  import numpy as np
  import cv2
  
  help_message = '''
  USAGE: peopledetect.py &lt;image_names&gt; ...
  
  Press any key to continue, ESC to stop.
  '''
  
  def inside(r, q):
      rx, ry, rw, rh = r
      qx, qy, qw, qh = q
      return rx &gt; qx and ry &gt; qy and rx + rw &lt; qx + qw and ry + rh &lt; qy + qh
  
  def draw_detections(img, rects, thickness = 1):
      for x, y, w, h in rects:
          # the HOG detector returns slightly larger rectangles than the real objects.
          # so we slightly shrink the rectangles to get a nicer output.
          pad_w, pad_h = int(0.15*w), int(0.05*h)
          cv2.rectangle(img, (x+pad_w, y+pad_h), (x+w-pad_w, y+h-pad_h), (0, 255, 0), thickness)
  
  
  if __name__ == '__main__':
      import sys
      from glob import glob
      import itertools as it
  
      print help_message
  
      hog = cv2.HOGDescriptor()
      hog.setSVMDetector( cv2.HOGDescriptor_getDefaultPeopleDetector() )
  
      for fn in it.chain(*map(glob, sys.argv[1:])):
          print fn, ' - ',
          try:
              img = cv2.imread(fn)
          except:
              print 'loading error'
              continue
  
          found, w = hog.detectMultiScale(img, winStride=(8,8), padding=(32,32), scale=1.05)
          found_filtered = []
          for ri, r in enumerate(found):
              for qi, q in enumerate(found):
                  if ri != qi and inside(r, q):
                      break
              else:
                  found_filtered.append(r)
          draw_detections(img, found)
          draw_detections(img, found_filtered, 3)
          print '%d (%d) found' % (len(found_filtered), len(found))
          cv2.imshow('img', img)
          ch = 0xFF &amp; cv2.waitKey()
          if ch == 27:
              break
      cv2.destroyAllWindows()
  </code></pre>
  
  <p>To be honest, I don't really understand principle of HOG.</p>
  
  <p>I prepare some image from opencv website and try to do some basic test by using this code, maybe like this..</p>
  
  <pre><code>$ ./peopledetect.py abba.png
  $ ./peopledetect.py luna.jpg
  </code></pre>
  
  <p>but I don't see any retangle drawed within code on display, maybe I did wrong.. could someone help me? thanks so much..</p>
  
  <p><img src="https://i.stack.imgur.com/r4QGt.png" alt="abba.png"><img src="https://i.stack.imgur.com/lHV8B.jpg" alt="luan.jpg"></p>