Python OpenCV – getRotationMatrix2D() Function

Last Updated : 03 Jan, 2023

cv2.getRotationMatrix2D() function is used to make the transformation matrix M which will be used for rotating a image.

Syntax:

cv2.getRotationMatrix2D(center, angle, scale)

Parameters:

center: Center of rotation
angle(θ): Angle of Rotation. Angle is positive for anti-clockwise and negative for clockwise.
scale: scaling factor which scales the image

Return: 2×3 Rotation Matrix M

M = $\begin{bmatrix} \alpha & \beta & (1-\alpha)\cdot c_x-\beta \cdot c_y\\ -\beta & \alpha & \beta\cdot c_x+(1-\alpha) \cdot c_y \end{bmatrix}$

where,

$\alpha = scale\cdot cos(\theta)\\ \beta = scale\cdot sin(\theta)\\ c_x\ and\ c_y\ are\ the\ coordinates\ of\ the\ center\ of\ the\ image.\\$

This is a type of affine transformation. An affine transformation is transformation which preserves lines and parallelism. These transformation matrix are taken by warpaffine() function as parameter and the rotated image will be returned.

Image Used:

Example 1:

Python3

import cv2 
  
# Reading the image 
image = cv2.imread('image.jpeg') 
  
# Extracting height and width from  
# image shape 
height, width = image.shape[:2] 
  
# get the center coordinates of the 
# image to create the 2D rotation 
# matrix 
center = (width/2, height/2) 
  
# using cv2.getRotationMatrix2D()  
# to get the rotation matrix 
rotate_matrix = cv2.getRotationMatrix2D(center=center, angle=90, scale=1) 
  
# rotate the image using cv2.warpAffine  
# 90 degree anticlockwise 
rotated_image = cv2.warpAffine( 
    src=image, M=rotate_matrix, dsize=(width, height)) 
  
cv2.imshow("rotated image:", rotated_image) 
cv2.imwrite('rotated_image.jpg', rotated_image) 

Output-

Example 2:

Python3

import cv2 
  
# Reading the image 
image = cv2.imread('image.jpeg') 
  
# Extracting height and width from  
# image shape 
height, width = image.shape[:2] 
  
# get the center coordinates of the  
# image to create the 2D rotation matrix 
center = (width/2, height/2) 
  
# using cv2.getRotationMatrix2D() to get 
# the rotation matrix 
rotate_matrix = cv2.getRotationMatrix2D(center=center, angle=-90, scale=1) 
  
# rotate the image using cv2.warpAffine 90  
# degree clockwise 
rotated_image = cv2.warpAffine( 
    src=image, M=rotate_matrix, dsize=(width, height)) 
  
cv2.imshow("rotated image:",rotated_image) 
cv2.imwrite('rotated_image.jpg', rotated_image) 

Output-

Python3

import cv2 
  
# Reading the image 
image = cv2.imread('image.jpeg') 
  
# Extracting height and width from image shape 
height, width = image.shape[:2] 
  
# get the center coordinates of the image to  
# create the 2D rotation matrix 
center = (width/2, height/2) 
  
# using cv2.getRotationMatrix2D() to get  
# the rotation matrix 
rotate_matrix = cv2.getRotationMatrix2D(center=center, angle=180, scale=1) 
  
# rotate the image using cv2.warpAffine 180  
# degree anticlockwise 
rotated_image = cv2.warpAffine( 
    src=image, M=rotate_matrix, dsize=(width, height)) 
  
cv2.imshow("rotated image:", rotated_image) 
cv2.imwrite('rotated_image.jpg', rotated_image) 

Output-

Example 4:

Python3

import cv2 
  
# Reading the image 
image = cv2.imread('image.jpeg') 
  
# Extracting height and width from image shape 
height, width = image.shape[:2] 
  
# get the center coordinates of the image to 
# create the 2D rotation matrix 
center = (width/2, height/2) 
  
# using cv2.getRotationMatrix2D() to get the 
# rotation matrix 
rotate_matrix = cv2.getRotationMatrix2D(center=center, angle=-180, scale=1) 
  
# rotate the image using cv2.warpAffine 180 
# degree clockwise 
rotated_image = cv2.warpAffine( 
    src=image, M=rotate_matrix, dsize=(width, height)) 
  
cv2.imshow("rotated image:", rotated_image) 
cv2.imwrite('rotated_image.jpg', rotated_image) 

Output –

Suggest improvement

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Python OpenCV – getRotationMatrix2D() Function

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