title: how to Count the number of non zero pixels of the canny image in my python program
body: <p>I'm trying to find the number of non zero pixels of the canny image, <em>could you help?</em></p>
  
  <p>Here is my code:</p>
  
  <pre><code>import cv
  def doCanny(input, lowThresh, highThresh, aperture):
      if input.nChannels != 1:
              return(0)
      out = cv.CreateImage((input.width, input.height), input.depth, 1)
      cv.Canny(input, out, lowThresh, highThresh, aperture)
      return out
  def doPyrDown(input):
      assert(input.width !=0 and input.height !=0)
      out = cv.CreateImage((input.width/2, input.height/2), input.depth, input.nChannels)
      cv.PyrDown(input, out)
      return out
  
  img = cv.LoadImage('mypic.jpg')
  img2 = cv.CreateImage((img.width, img.height), img.depth, 1)
  cv.CvtColor(img, img2, cv.CV_BGR2GRAY)
  cv.NamedWindow("Example GRAY", cv.CV_WINDOW_AUTOSIZE)
  cv.ShowImage("Example GRAY", img2)
  img3 = doCanny(img2, 10, 100, 3)
  img2 = doPyrDown(img3)
  cv.ShowImage("Example 2", img2)
  cv.WaitKey(0)
  </code></pre>