circle_detector.py

import cv2
import numpy as np
import matplotlib.pyplot as plt
import sys

# load the image
img = cv2.imread(sys.argv[1])
# convert BGR to RGB to be suitable for showing using matplotlib library
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
# make a copy of the original image
cimg = img.copy()
# convert image to grayscale
img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# apply a blur using the median filter
img = cv2.medianBlur(img, 5)
# finds the circles in the grayscale image using the Hough transform
circles = cv2.HoughCircles(image=img, method=cv2.HOUGH_GRADIENT, dp=0.9, 
                            minDist=80, param1=110, param2=39, maxRadius=70)

for co, i in enumerate(circles[0, :], start=1):
    # draw the outer circle in green
    cv2.circle(cimg,(i[0],i[1]),i[2],(0,255,0),2)
    # draw the center of the circle in red
    cv2.circle(cimg,(i[0],i[1]),2,(0,0,255),3)
    
# print the number of circles detected
print("Number of circles detected:", co)
# save the image, convert to BGR to save with proper colors
# cv2.imwrite("coins_circles_detected.png", cimg)
# show the image
plt.imshow(cimg)
plt.show()