Computer Vision with Python and OpenCV2 (Part 2 - Rotating and flipping images)

01 September 2019 - 7 mins read time

Contents:

You can download the jupyter notebook or the project from GitHub here: Github project link

Picture used in this tutorial is downloaded from www.pexels.com. I do not own the picture. Picture is available for free download and complete credits goes to Chevanon Photography. Link below.

Credit: Photo by Chevanon Photography from Pexels

PEXELS PHOTO DOWNLOAD LINK

Note:

I used greeshot software to add labels 1 and 2 on the original picture

OpenCV2 has 3 kinds of rotations available

  1. cv2.ROTATE_90_CLOCKWISE
  2. cv2.ROTATE_90_COUNTER_CLOCKWISE
  3. cv2.ROTATE_180

OpenCV2 has 3 kinds of flips available

  1. flipCode = 0 (to flip vertically)
  2. flipCode > 0 (to flip horizontally)
  3. flipCode < 0 (to flip vertically first and then flip it horizontally)

Load libraries

import cv2

import matplotlib.pyplot as plt
%matplotlib inline

Display original image

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)

plt.figure(figsize=(15,10))
plt.imshow(puppies)

Rotating by 90 degrees clockwise

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)
puppies_rotated = cv2.rotate(puppies, cv2.ROTATE_90_CLOCKWISE)

plt.figure(figsize=(10,15))
plt.imshow(puppies_rotated)

Rotating by 90 degrees counter-clockwise

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)
puppies_rotated = cv2.rotate(puppies, cv2.ROTATE_90_COUNTERCLOCKWISE)

plt.figure(figsize=(10,15))
plt.imshow(puppies_rotated)

Rotating by 180 degrees

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)
puppies_rotated = cv2.rotate(puppies, cv2.ROTATE_180)

plt.figure(figsize=(15,10))
plt.imshow(puppies_rotated)

Flipping an image upside down (vertically with flipcode = 0)

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)
puppies_rotated = cv2.flip(src=puppies, flipCode=0)

plt.figure(figsize=(15,10))
plt.imshow(puppies_rotated)

Flipping an image horizontally (with flipcode > 0)

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)
puppies_rotated = cv2.flip(src=puppies, flipCode=1)

plt.figure(figsize=(15,10))
plt.imshow(puppies_rotated)

Flipping an image vertically and horizontally (flipCode < 0)

Meaning, image is first flipped vertically (upside down), then flipped horizontally (left to right)

puppies = cv2.imread('puppies2.png')

puppies = cv2.cvtColor(puppies, cv2.COLOR_BGR2RGB)
puppies_rotated = cv2.flip(src=puppies, flipCode=-1)

plt.figure(figsize=(15,10))
plt.imshow(puppies_rotated)

Python script to rotate and flip images

Find the script file in the github project working folder -> rotate_and_flip_images.py

# Import library
import cv2

# Load default image
puppies = cv2.imread('puppies2.png')

def rotate(x):    
    """
    rotate() function takes a parameter x (integer value) and outputs a window with default image
    
    if x = 1:
    default image will be rotated 90 degrees clockwise
    
    if x = 2:
    default image will be rotated 90 degress counter-clockwise
    
    if x = 3:
    default image will be rotated 180 degrees
    """
    try:
        if int(x) == 1:
            puppies_rotated = cv2.rotate(puppies, cv2.ROTATE_90_CLOCKWISE)
        elif int(x) == 2:
            puppies_rotated = cv2.rotate(puppies, cv2.ROTATE_90_COUNTERCLOCKWISE)
        elif int(x) == 3:
            puppies_rotated = cv2.rotate(puppies, cv2.ROTATE_180)
        else:
            print("Sorry invalid option")       
            
        cv2.namedWindow('rotateoutput', cv2.WINDOW_NORMAL)
        cv2.resizeWindow('rotateoutput', (600,600))
        cv2.imshow('rotateoutput', puppies_rotated)  
        cv2.waitKey(0)
        cv2.destroyAllWindows()
    except:
        print("Sorry invalid option")

def flip(y):    
    """
    flip() function takes a parameter y (integer value) and outputs a window with default image
    
    if y = 1:
    default image will be flipped vertcially or upside down (i.e., flipCode = 0)
    
    if y = 2:
    default image will be flipped horizontally with flipCode > 0 (i.e., flipCode = 1)
    
    if y = 3:
    default image will be flipped image vertically and horizontally, meaning image is first flipped vertically (upside down), then flipped horizontally (left to right) with flipCode < 0 (i.e., flipCode = -1)
    """
    try:
        if int(y) == 1:
            puppies_rotated = cv2.flip(src=puppies, flipCode=0)
        elif int(y) == 2:
            puppies_rotated = cv2.flip(src=puppies, flipCode=1)
        elif int(y) == 3:
            puppies_rotated = cv2.flip(src=puppies, flipCode=-1)
        else:
            print("Sorry invalid option")        
        
        cv2.namedWindow('flipoutput', cv2.WINDOW_NORMAL)
        cv2.resizeWindow('flipoutput', (600,600))
        cv2.imshow('flipoutput', puppies_rotated)  
        cv2.waitKey(0)
        cv2.destroyAllWindows()
    except:
        print("Sorry invalid option")
# calling rotate() function with parameter value = 3 i.e., rotating 180 degrees
rotate(3)

# calling flip() function with parameter value = 3 i.e., flipping image with flipCode = -1 (which is < 0)
flip(3)

Running python script from jupyter notebook

To run python script in jupyter, use the jupyter’s inline magic function %run to run

%run rotate_and_flip_images.py

⇠ Computer Vision with Python and OpenCV2 (Part 1 - Basics)

Web Scraping in Python 3 ⇢