Crop image simple app using cv2 NumPy python

In this blog we are going to learn how to make  a simple app to crop an image in python using numpy , cv2(openCV).

Code

import cv2

import numpy as np

img = cv2.imread('cat.jpg')

img_dup = np.copy(img)

mouse_pressed = False

#defining starting and ending point of rectangle (crop image region)

starting_x=starting_y=ending_x=ending_y= -1

def mousebutton(event,x,y,flags,param):

    global img_dup , starting_x,starting_y,ending_x,ending_y,mouse_pressed

    #if left mouse button is pressed then takes the cursor position at starting_x and starting_y 

    if event == cv2.EVENT_LBUTTONDOWN:

        mouse_pressed= True

        starting_x,starting_y=x,y

        img_dup= np.copy(img)

   

    elif event == cv2.EVENT_MOUSEMOVE:

        if mouse_pressed:

            img_dup = np.copy(img)

            cv2.rectangle(img_dup,(starting_x,starting_y),(x,y),(0,255,0),1)

    #final position of rectange if left mouse button is up then takes the cursor position at ending_x and ending_y 

    elif event == cv2.EVENT_LBUTTONUP:

        mouse_pressed=False

        ending_x,ending_y= x,y

cv2.namedWindow('image')

cv2.setMouseCallback('image',mousebutton)

while True:

    cv2.imshow('image',img_dup)

    k= cv2.waitKey(1)

    if k==ord('c'):

        #remove these condition and try to play weird output will give you idea why its done

        if starting_y>ending_y:

            starting_y,ending_y= ending_y,starting_y

        if starting_x>ending_x:

            starting_x,ending_x= ending_x,starting_x

        if ending_y-starting_y>1  and ending_x-starting_x>0:

            image = img[starting_y:ending_y,starting_x:ending_x]

            img_dup= np.copy(image)

        elif k == 27:

            break

cv2.destroyAllWindows()