cv/geometry/circle.py

import cv2
import numpy as np

# define a video capture object
vid = cv2.VideoCapture(0)

while(True):

    # Capture the video frame
    # by frame
    ret, frame = vid.read()

    # Convert to grayscale.
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Blur using 3 * 3 kernel.
    gray_blurred = cv2.blur(gray, (3, 3))

    # Apply Hough transform on the blurred image.
    detected_circles = cv2.HoughCircles(gray_blurred, 
                    cv2.HOUGH_GRADIENT, 1, 1000, param1 = 60,
                param2 = 30, minRadius = 100, maxRadius = 200)

    # Draw circles that are detected.
    if detected_circles is not None:

        # Convert the circle parameters a, b and r to integers.
        detected_circles = np.uint16(np.around(detected_circles))

        for pt in detected_circles[0, :]:
            a, b, r = pt[0], pt[1], pt[2]

            # Draw the circumference of the circle.
            cv2.circle(frame, (a, b), r, (0, 255, 0), 2)

            # Draw a small circle (of radius 1) to show the center.
            cv2.circle(frame, (a, b), 1, (0, 0, 255), 3)

    # Display the resulting frame
    cv2.imshow('frame', frame)

    # the 'q' button is set as the
    # quitting button you may use any
    # desired button of your choice
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# After the loop release the cap object
vid.release()
# Destroy all the windows
cv2.destroyAllWindows()