how to Count the number of non zero pixels of the canny image in my python program

Question

I'm trying to find the number of non zero pixels of the canny image, could you help?

Here is my 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)

Answer 1

You can use opencv's function countNonZero for counting the number of non-zero pixels in the image.

img3 = doCanny(img2, 10, 100, 3)
nzCount = cv.CountNonZero(img3);

Update:

In newer versions of OpenCV, the function to count non zeros has been updated as follows:

nzCount = cv2.countNonZero(img3)

Answer 2

Try cv.countNonZero(), CountNonZero() doesn't work for me.