opencv/samples/python2/houghcircles.py

#!/usr/bin/python

'''
This example illustrates how to use cv2.HoughCircles() function.
Usage: ./houghcircles.py [<image_name>]
image argument defaults to ../data/board.jpg
'''

import cv2
import numpy as np
import sys


print __doc__
try:
    fn = sys.argv[1]
except:
    fn = "../data/board.jpg"

src = cv2.imread(fn, 1)
img = cv2.cvtColor(src, cv2.COLOR_BGR2GRAY)
img = cv2.medianBlur(img, 5)
cimg = src.copy() # numpy function

circles = cv2.HoughCircles(img, cv2.HOUGH_GRADIENT, 1, 10, np.array([]), 100, 30, 1, 30)
a, b, c = circles.shape
for i in range(b):
    cv2.circle(cimg, (circles[0][i][0], circles[0][i][1]), circles[0][i][2], (0, 0, 255), 3, cv2.LINE_AA)
    cv2.circle(cimg, (circles[0][i][0], circles[0][i][1]), 2, (0, 255, 0), 3, cv2.LINE_AA) # draw center of circle

cv2.imshow("source", src)
cv2.imshow("detected circles", cimg)
cv2.waitKey(0)