How to get the coordinates of the cv2.imshow window?

Question

I am using this code

import numpy as np
import cv2
from PIL import ImageGrab as ig
import time

last_time = time.time()
while(True):
    screen = ig.grab(bbox=(200, 200, 600, 600))
    print('Loop took {} seconds'.format(time.time()-last_time))
    cv2.imshow("test", np.array(screen))
    last_time = time.time()
    if cv2.waitKey(25) & 0xFF == ord('q'):
        cv2.destroyAllWindows()
        break

from this question on SO. This is my output:

output

This works fine. I am looking for a solution where I can capture the area just under the output window. When I move the window around, the output changes as well. One way would be to update this line as follows:

screen = ig.grab(bbox=(x1, y2, x2, y2))

but thing I can't figure out is that how to get these parameters values. Or how to get the coordinates of the output window?

P.S. I don't have enough reputation to embed images here directly so I added the external link.