title: Can I blend or get rid of null pixels in my images?
body: <p>Using opencv, I'm detecting circles in my images.</p>
  
  <p>I get the "Unrecognized or unsupported array type in function cvGetMat" error. Other questions with this error mentioned null pixels, which some of my pictures do have. Can I get rid of the null pixels before the function where the error happens executes?</p>
  
  <p>Additionally, I've been able to run the bit of code on the images with null pixels before. This error is only occurring when I try to it over a set of images with a for loop.</p>
  
  <pre><code>for i in range (1, 9):
      filename = 'motrans/motrans_images_june/AMR' + str(i) + '.png'
      img = cv2.imread(filename, 0)
      img = cv2.medianBlur(img, 1)
      cimg = cv2.cvtColor(img,cv2.COLOR_GRAY2BGR)
      circles = cv2.HoughCircles(img, cv.CV_HOUGH_GRADIENT, 1, 300, param1=60, param2=20, minRadius=55, maxRadius=75) #3
  </code></pre>
  
  <p>The error occurs at cv2.HoughCircles.</p>