imwrite turns image upside down

edit

Hello everyone.

I am reading all the frames from a video and saving them in .png picutres.

The imwrite command is saving all the images upside down.. how do I write them in righ orientation? I would try it with windows tool, but it takes more than 15minutes to turn all the 4600 images to the right orientation...

What am I missing? Below follows my code:

" import cv2 import math

def main():

cap = cv2.VideoCapture('finos.mp4')    
i = 1

while (cap.isOpened()):

    ret, frame = cap.read()

    if (ret != True):
        break

    filename = './test/image' +  str(int(i)) + ".png";i+=1
    cv2.imwrite(filename, frame)
    if cv2.waitKey(1) == 27: # exit on ESC
        break

cap.release()
cv2.destroyAllWindows()

if __name__ == "__main__": main() "

Thanks in advance :)