find green ball

import cv2
import numpy as np

cap = cv2.VideoCapture(0)

kernel = np.ones((8,8),np.uint8)

while(1):

    # Take each frame
    _, frame = cap.read()
    frame = cv2.flip(frame,1)

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

    # define range of green color in HSV
    lower_blue = np.array([50,50,50])
    upper_blue = np.array([90,255,255])

    # Threshold the HSV image to get only green colors
    mask = cv2.inRange(hsv, lower_blue, upper_blue)
    mask = cv2.morphologyEx(mask, cv2.MORPH_OPEN, kernel)
    
    # Bitwise-AND mask and original image
    res = cv2.bitwise_and(frame,frame, mask= mask)

    a,b = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

    for cnt in a:
        (x,y),radius = cv2.minEnclosingCircle(cnt)
        center = (int(x),int(y))
        if radius > 20:
            radius = int(radius)
            cv2.circle(frame,center,radius,(0,120,255),-1)
            cv2.line(frame, (center[0]-50,center[1]), (center[0]+50,center[1]), (0,0,0),3)
            cv2.line(frame, (center[0],center[1]-50), (center[0],center[1]+50), (0,0,0),3)
            
    cv2.imshow('frame',frame)
    cv2.imshow('mask',mask)
    cv2.imshow('res',res)
    #cv2.imshow('open',opening)
    k = cv2.waitKey(5) & 0xFF
    if k == 27:
        break