Operating on images using OpenCV-Python

Let's take a look at how to operate on images using OpenCV-Python. In this recipe, we will see how to load and display an image. We will also look at how to crop, resize, and save an image to an output file.

How to do it…

1. Create a new Python file, and import the following packages:

   import sys
   
   import cv2
   import numpy as np

2. Specify the input image as the first argument to the file, and read it using the image read function. We will use forest.jpg, as follows:

   # Load and display an image -- 'forest.jpg'
   input_file = sys.argv[1]
   img = cv2.imread(input_file)

3. Display the input image, as follows:

   cv2.imshow('Original', img)

4. We will now crop this image. Extract the height and width of the input image, and then specify the boundaries:

   # Cropping an image
   h, w = img.shape[:2]
   start_row, end_row = int(0.21*h), int(0.73*h)
   start_col, end_col= int(0.37*w), int(0.92*w)

5. Crop the image using NumPy style slicing and display it:

   img_cropped = img[start_row:end_row, start_col...