Interacting with a live video stream

Let's see how we can use the mouse to interact with a live video stream from the webcam. We can use the mouse to select a region, and then apply a negative film effect on that region, as shown in the following image:

In the following program, we will capture the video stream from the webcam, select a region of interest with the mouse, and then apply this effect:

import cv2 
import numpy as np 

def update_pts(params, x, y):
    global x_init, y_init
    params["top_left_pt"] = (min(x_init, x), min(y_init, y))
    params["bottom_right_pt"] = (max(x_init, x), max(y_init, y))
    img[y_init:y, x_init:x] = 255 - img[y_init:y, x_init:x]
 
def draw_rectangle(event, x, y, flags, params): 
    global x_init, y_init, drawing
    # First click initialize the init rectangle point 
    if event == cv2.EVENT_LBUTTONDOWN:
        drawing = True 
        x_init, y_init = x, y 
    # Meanwhile mouse button is pressed, update diagonal rectangle point 
    elif event ==...