OpenCV 3 Computer Vision with Python Cookbook

How to do it...

1. Import all of the necessary modules, open an image, and display it on the screen:

import cv2, randomimport numpy as npimg = cv2.imread('bw.png', cv2.IMREAD_GRAYSCALE)

2. Find the contours of the image and display them:

im2, contours, hierarchy = cv2.findContours(img, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)color = cv2.cvtColor(img, cv2.COLOR_GRAY2BGR)cv2.drawContours(color, contours, -1, (0,255,0), 3)cv2.imshow('contours', color)cv2.waitKey()cv2.destroyAllWindows()

3. Define a callback function to handle a user click on the image. This function draws a small circle where the click has happened, and the color of the circle is determined by whether the click was inside or outside of the contour:

contour = contours[0]image_to_show ...