title: circle detection in open cv using python
body: <p>I was trying to detect circles from a black background with red circular kind objects.</p>
  
  <pre><code>import cv2
  import cv2.cv as cv
  import numpy as np
  
  img = cv2.imread('extracted.jpg',0)
  img = cv2.medianBlur(img,5)
  cimg = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
  
  circles = cv2.HoughCircles(img,cv.CV_HOUGH_GRADIENT,1,20,
                          param1=50,param2=30,minRadius=0,maxRadius=0)
  
  circles = np.uint8(np.around(circles))
  for i in circles[0,:]:
     # draw the outer circle
     cv2.circle(cimg,(i[0],i[1]),i[2],(0,255,0),2)
     # draw the center of the circle
     cv2.circle(cimg,(i[0],i[1]),2,(0,0,255),3)
  
  cv2.imshow('detected circles',cimg)
  cv2.waitKey(0)
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>I have loaded the image in grayscale mode,still it gives me an error </p>
  
  <pre><code>"circles = np.uint8(np.around(circles))
  File "/usr/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 2277, in around
    return _wrapit(a, 'round', decimals, out)
  File "/usr/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 37, in _wrapit
    result = getattr(asarray(obj),method)(*args, **kwds)
  AttributeError: rint"
  </code></pre>
  
  <p>I cannot post the image because of my present reputation.</p>