Crop rectangle out of image using mouse clicks

manual_crop.py

import cv2, numpy as np

# Click on one corner of the image,
# then, click on the other corner on the image.
# The image will be cropped and saved into the folder (see below)

# Press 'esc' to quit

# Before you begin, change the path to you own video:
cap = cv2.VideoCapture('/home/stephen/Desktop/track.MP4')

# Also, create a folder for the cropped images, and change this path to that folder:
path_to_cropped_images = '/home/stephen/Desktop/car_images/'

#mouse callback function
global click_list
global positions
positions, click_list = [], []

def callback(event, x, y, flags, param):
    if event == 1: click_list.append((x,y))
    positions.append((x,y))    
    
cv2.namedWindow('img')
cv2.setMouseCallback('img', callback)
image_number = 0

#read first image
ret, img_p = cap.read()
img_p = cv2.resize(img_p, (640,480))
    
while True:
    img = img_p.copy()

    if len(click_list)>0:
        
        mouse_position = positions[-1]        
        
        a = click_list[-1][0], click_list[-1][1]
        b = mouse_position[0], click_list[-1][1]
        cv2.line(img, a, b, (123,234,123), 3)
        
        a = click_list[-1][0], mouse_position[1]
        b = mouse_position[0], mouse_position[1]
        cv2.line(img, a, b, (123,234,123), 3)
        
        a = mouse_position[0], click_list[-1][1]
        b = mouse_position[0], mouse_position[1]
        cv2.line(img, a, b, (123,234,123), 3)
        
        a = click_list[-1][0], mouse_position[1]
        b = click_list[-1][0], click_list[-1][1]
        cv2.line(img, a, b, (123,234,123), 3)


    # If there are four points in the click list, save the image
    if len(click_list) == 2:

        #get the top left and bottom right
        a,b  = click_list
        top = max(a[1], b[1])
        bottom = min(a[1], b[1])
        right = max(a[0], b[0])
        left = min(a[0], b[0])
        print(a,b, bottom, top, left, right)

        # crop out the object in the image
        crop = img[bottom: top, left: right]
        #write to the folder
        cv2.imwrite(path_to_cropped_images+str(image_number)+'.png', crop)

        #reset the click list
        click_list = []
        image_number += 1
        
        # read next image
        ret, img = cap.read()
        img_p = cv2.resize(img, (640,480))
        img = img_p.copy()

    # try to paste the cropped image into the upper left corner
    try:
        hh,ww,xx = crop.shape
        crop_resize = cv2.resize(crop, (int(ww/2), int(hh/2)))
        hh,ww,xx = crop_resize.shape
        img[0:hh, 0:ww]  = crop_resize
    except: pass

    # show the image and wait
    cv2.imshow('img', img)
    k = cv2.waitKey(1)    
    if k == 27: break
    
cv2.destroyAllWindows()