OpenCV 3 Computer Vision with Python Cookbook

How to do it...

The steps for this recipe are as follows:

1. First, load an image and make its copy:

import cv2, numpy as npimage = cv2.imread('../data/Lena.png')image_to_show = np.copy(image)

2. Now, define some variables to store the mouse state:

mouse_pressed = Falses_x = s_y = e_x = e_y = -1

3. Let's implement a handler for mouse events. This should be a function that takes four arguments, as follows:

def mouse_callback(event, x, y, flags, param):    global image_to_show, s_x, s_y, e_x, e_y, mouse_pressed    if event == cv2.EVENT_LBUTTONDOWN:        mouse_pressed = True        s_x, s_y = x, y        image_to_show = np.copy(image)    elif event == cv2.EVENT_MOUSEMOVE:        if mouse_pressed:            image_to_show = np.copy(image)            cv2.rectangle(image_to_show, (s_x, s_y), (x, y), (0, ...