How To Use Mouse Clicks To Draw Circles In Python Using OpenCV - Easy Project - 2024

In today’s very short blog we will see that how we can use mouse clicks to draw circles in Python using OpenCV. This is going to be a fun application. So let’s tighten our belts and dive straight into it.

Table of Contents

Step 1 – Import necessary libraries to draw circles.

import cv2
import numpy as np

Step 2 – Let’s create a black image.

black_image = np.zeros((512,512,3),np.uint8)
cv2.imshow('Black Image', black_image)

NOTE – Read more about it here.

Step 3 – Create a draw circles function.

def draw_circles(event,x,y,flags,param):
    if event==cv2.EVENT_LBUTTONDOWN:
        cv2.circle(black_image,(x,y),40,(255,255,255),-1)

event here refers to any of the mouse operation.
(x,y) are the coordinates of the point where we have clicked.
Then we are checking if the event is equal to the left button click then draw a white-colored circle centered at (x,y) with a radius of 40 pixels and filled with white color (because the thickness is passed as -1).

Step 4 – Run an infinite loop…

# draw circles
while True:
    cv2.setMouseCallback('win',draw_circles)
    cv2.imshow('win',black_image)
    if cv2.waitKey(1)==27:
        break

In the first line, we have used cv2.setMouseCallback() to bind the draw circles() function with the ‘win’ window. It means that as soon as something is done using the mouse on the ‘win’ window, immediately go to the draw_circles function and run that function.
After that, we are just showing our black image with white circles drawn on it.
And at last, if the ESC key(ASCII 27) is pressed break the code.

Let’s see the whole code…

import cv2
import numpy as np

black_image = np.zeros((512, 512, 3), np.uint8)
cv2.imshow('Black Image', black)

def draw_circles(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDOWN:
        cv2.circle(black_image, (x, y), 40, (255, 255, 255), -1)

while True:
    cv2.setMouseCallback('win', draw_circles)
    cv2.imshow('win', black_image)
    if cv2.waitKey(1) == 27:
        break
cv2.destroyAllWindows()