In this article we want to learn How to Rotate an Image with OpenCV and Python, OpenCV is an open source computer vision and machine learning library that provides different tools and techniques for image processing and manipulation. one of the common image processing tasks is to rotate an image. In this article we are going to explore how to rotate an image using OpenCV and Python.
First of all we need to install Python OpenCV
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pip install opencv-python |
Now we need to import our required libraries from OpenCV
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import cv2 |
After that we need to load the image that we want to rotate. we can use cv2.imread() function to read an image from the disk. this function takes the file path as the input and returns NumPy array that represents the image.
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img = cv2.imread('lena.tif') |
For rotating an image we need to define rotation matrix. rotation matrix is 2×3 matrix that defines transformation that needs to be applied to image. matrix takes three arguments: angle of rotation, center of rotation and scale of the image.
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(h, w) = img.shape[:2] center = (w / 2, h / 2) angle = 45 scale = 1.0 M = cv2.getRotationMatrix2D(center, angle, scale) |
In the above code first of all we have get height and width of the image using shape attribute of NumPy array. after that we calculate center of the image using height and width. we set angle of rotation to 45 degrees and scale of the image to 1.0, and finally we use the cv2.getRotationMatrix2D() function to generate the rotation matrix.
Once we have rotation matrix, we can apply it to the image using cv2.warpAffine() function. this function takes input image, rotation matrix, and size of the output image as the input arguments.
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rotated = cv2.warpAffine(img, M, (w, h)) |
In the above code we have used cv2.warpAffine() function to apply the rotation matrix to the input image. after that we pass input image, rotation matrix, and size of the output image as the input arguments.
Finally we can display rotated image using cv2.imshow() function. we pass title of the window and image array as the input arguments.
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cv2.imshow("Rotated Image", rotated) cv2.waitKey(0) cv2.destroyAllWindows() |
In the above code we have used cv2.imshow() function to display rotated image in new window. after that we have used wait for key press using cv2.waitKey() function. and finally we have used cv2.destroyAllWindows() function to close all the windows.
This is the complete code for this article
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import cv2 # Load image img = cv2.imread('lena.tif') # Get height and width of image (h, w) = img.shape[:2] # Calculate center of image center = (w / 2, h / 2) # Set angl of rotation angle = 45 # Set scale of the image scale = 1.0 # Define rotation matrix M = cv2.getRotationMatrix2D(center, angle, scale) # Apply rotation matrix to the image rotated = cv2.warpAffine(img, M, (w, h)) # Display rotated image cv2.imshow("Rotated Image", rotated) # Wait for a key press and then close all windows cv2.waitKey(0) cv2.destroyAllWindows() |
Run the complete code and this will be the result
In this article we have leaned how to rotate an image using OpenCV and Python. also we have learned how to load an image, define rotation matrix, apply rotation matrix to the image and display rotated image. OpenCV provides powerful set of tools for image processing and manipulation, and rotating an image is just one of the many tasks that can be performed using OpenCV.
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