Easiest way to rotate by 90 degrees an image using OpenCV?

Question

What is the best way (in c/c++) to rotate an IplImage/cv::Mat by 90 degrees? I would assume that there must be something better than transforming it using a matrix, but I ca

Answer 1

Rotation is a composition of a transpose and a flip.

Which in OpenCV can be written like this (Python example below):

img = cv.LoadImage("path_to_image.jpg")
timg = cv.CreateImage((img.height,img.width), img.depth, img.channels) # transposed image

# rotate counter-clockwise
cv.Transpose(img,timg)
cv.Flip(timg,timg,flipMode=0)
cv.SaveImage("rotated_counter_clockwise.jpg", timg)

# rotate clockwise
cv.Transpose(img,timg)
cv.Flip(timg,timg,flipMode=1)
cv.SaveImage("rotated_clockwise.jpg", timg)