Open CV example for finding the number of circles in an image

find_circles.py

# Tuned to find the number of balls/circles in this image https://i.redd.it/z092hx3k89qy.jpg

import cv2
import cv2.cv as cv
import numpy as np

img = cv2.imread('circles.jpg')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

circles = cv2.HoughCircles(gray, cv2.cv.CV_HOUGH_GRADIENT, 1, 3,
              param1=170, #this controls the edge detection thresholds - 170-200 produces reasonable results all in that 20k-30k range
              param2=10,
              minRadius=2,
              maxRadius=30)

print len(circles[0,:])   #this is the answer we care about
circles = np.uint16(np.around(circles))
for i in circles[0,:]:
    cv2.circle(img,(i[0],i[1]),2,(0,0,255),3)

cv2.imshow('detected circles',img) #show the image with all found circles highlighted as a sanity check
cv2.waitKey(0)
cv2.destroyAllWindows()