Get Coordinates of Clicked Points in an Image using Python

get coordinates of clicked points in an image using a python program

Introduction

In this tutorial, we will learn how to find the coordinates of clicked points on an image using a Python program. Alternatively, you can consider this tutorial as an exploration of capturing mouse events in Python. This feature is useful when you want to use your mouse like a paintbrush and figure out the coordinates of points around a specific object in an image.

We’re going to use the Python OpenCV library to handle mouse events. According to the OpenCV Documentation, the library supports different types of mouse events. Let’s explore them.

All Mouse Events at a Glance

The OpenCV library offers various mouse events. Let’s find out all of them using a Python program.

import cv2 as cv
events = [i for i in dir(cv) if 'EVENT' in i]
print( events )

Output

[‘EVENT_FLAG_ALTKEY’, ‘EVENT_FLAG_CTRLKEY’, ‘EVENT_FLAG_LBUTTON’, ‘EVENT_FLAG_MBUTTON’, ‘EVENT_FLAG_RBUTTON’, ‘EVENT_FLAG_SHIFTKEY’, ‘EVENT_LBUTTONDBLCLK’, ‘EVENT_LBUTTONDOWN’, ‘EVENT_LBUTTONUP’, ‘EVENT_MBUTTONDBLCLK’, ‘EVENT_MBUTTONDOWN’, ‘EVENT_MBUTTONUP’, ‘EVENT_MOUSEHWHEEL’, ‘EVENT_MOUSEMOVE’, ‘EVENT_MOUSEWHEEL’, ‘EVENT_RBUTTONDBLCLK’, ‘EVENT_RBUTTONDOWN’, ‘EVENT_RBUTTONUP’]

Finding the coordinates of clicked points

As we’re interested in finding the coordinates of clicked points in an image, using “cv2.EVENT_LBUTTONDOWN” will befit for our task. Let’s make a program for it.

Importing the module

Let’s import the cv2 module.

import cv2

Creating the `Capture_Event` function

The Capture_Event function takes parameters related to mouse events. It checks if the left mouse button is pressed (‘cv2.EVENT_LBUTTONDOWN’) and, if true, prints the coordinates of the clicked point.

def Capture_Event(event, x, y, flags, params):
	# If the left mouse button is pressed
	if event == cv2.EVENT_LBUTTONDOWN:
		# Print the coordinate of the 
		# clicked point
		print(f"({x}, {y})")

The Main Execution Block

The code, within the main execution block, reads and displays the selected image, and sets up a mouse callback function using Capture_Event, waits for a key press to exit, and then closes all open windows.

Please read the file formats supported by OpenCV in the cv2.imread function by checking here.

if __name__=="__main__":
	# Read the Image.
	img = cv2.imread('Your Image Here', 1)
	# Show the Image
	cv2.imshow('image', img)
	# Set the Mouse Callback function, and call
	# the Capture_Event function.
	cv2.setMouseCallback('image', Capture_Event)
	# Press any key to exit
	cv2.waitKey(0)
	# Destroy all the windows
	cv2.destroyAllWindows()