How to resize window in opencv2 python

Yes, unfortunately you can't manually resize a nameWindow window without Qt backend. Your options:

• use cv2.resize function to resize the image to desired size prior to displaying the image
• install OpenCV with Qt backend support and use cv2.namedWindow("main", CV_WINDOW_NORMAL)

Simply write

cv2.namedWindow("main", cv2.WINDOW_NORMAL)

and then manually resize it to your desired size

cv2.resizeWindow('image', 900, 900)