Track a water bottle cap view by USB cam (use Python2 with open_cv 2 and numpy)

track_cap.py

import cv2
import numpy as np

# open_cv track test :
#
# track blue object and check there are in circle area
# for test: object is a blue water bottle cap (color H,S,V = 202 (101 after normalized, 64, 59)


# some class
class Circle(object):
    def __init__(self, center, radius):
        self.center = center
        self.radius = radius
        
    def is_inside(self, pos):
        return (pos[0] - self.center[0])**2 + (pos[1] - self.center[1])**2 < self.radius**2

# some vars
center = (0, 0)
i = 0

# link to USB cam /dev/video1
cap = cv2.VideoCapture(1)

# main loop
while True:
    # take each frame
    _, frame = cap.read()

    # convert BGR to HSV
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

    # define range of blue color in HSV
    lower_blue = np.array([92,50, 50])
    upper_blue = np.array([112,255,255])

    # threshold the HSV image to get only blue colors
    mask = cv2.inRange(hsv, lower_blue, upper_blue)
    mask = cv2.erode(mask, None, iterations=2)
    mask = cv2.dilate(mask, None, iterations=2)
    
    # find contours in the mask
    cnts = cv2.findContours(mask.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[-2]
    center = (0,0)
    radius = 0
    # if one or more contour(s) find
    if len(cnts) > 0:
        # use the larger area
        c = max(cnts, key=cv2.contourArea)
        # area as a circle
        ((x, y), radius) = cv2.minEnclosingCircle(c)
        M = cv2.moments(c)
        center = (int(M['m10'] / M['m00']), int(M['m01'] / M['m00']))
    
    # bitwise-AND mask and original image
    res = cv2.bitwise_and(frame,frame, mask= mask)

    # set circle
    c1 = Circle((400, 350), 20)

    # add cible
    cv2.circle(res, center, 5, (0,255,0), -1)
    cv2.circle(res, c1.center, c1.radius, (0,255,0), 0)

    # check if center is in target and large enough
    if radius > 20 and c1.is_inside(center):
        print('cap is in circle (#%d)' % i)
        i += 1

    # display all
    cv2.imshow('frame',frame)
    cv2.imshow('mask',mask)
    cv2.imshow('res',res)

    # manage escape key
    k = cv2.waitKey(5) & 0xFF
    if k == 27:
        break

cv2.destroyAllWindows()