Rotate the image via opencv in my defined function with Python

Question

I would like to rotate an image in my defined function and save the result in parameter for extra use in main function.

The codes are as below:

import cv2

def rotate(img1, img2):  # rotate img1 and save it in img2
    angle = 30  # rotated angle
    h, w, c = img1.shape

    m = cv2.getRotationMatrix2D((w/2, h/2), angle, 1)
    img2 = cv2.warpAffine(img1, m, (w, h))  # rotate the img1 to img2
    cv2.imwrite("rotate1.jpg", img2)  # save the rotated image within the function, successfully!

img = cv2.imread("test.jpg")
img_out = None

rotate(img, img_out)

cv2.imwrite("rotate2.jpg", img_out)  # save the rotated image in the main function, failed!

print("Finished!")

The result "img2" saved in function "rotate" is ok. But the one "img_out" from the function parameter is failed to save.

What's the problem with it? How can I resolve it without using the global variable? Thanks!

score 0 · Accepted Answer · edited May 23 '17 at 12:16

Modifications of parameters performed within a function will not be returned to the main program. You could also have a look here for further reading.

What you can do is return an image as shown in the code below:

import cv2

def rotate(img1):  # rotate img1 and save it in img
    angle = 30  # rotated angle
    h, w, c = img1.shape

    m = cv2.getRotationMatrix2D((w/2, h/2), angle, 1)
    img2 = cv2.warpAffine(img1, m, (w, h))  # rotate the img1 to img2
    cv2.imwrite("rotate1.jpg", img2)  # save the rotated image within the function, successfully!
    return img2

img = cv2.imread("image.jpg")

img_out=rotate(img)

cv2.imwrite("rotate2.jpg", img_out)  # save the rotated image in the main function, failed!

print("Finished!")

Rotate the image via opencv in my defined function with Python

1 Answers1