如何在python模块中使用cv2打开图像

Question

So this is the code I have and it works fine, as it should, it displays an image until you press a button:

import cv2
def open_img():
   template = cv2.imread('templates\\img_test.jpg')
   cv2.imshow('template', template)
   cv2.waitKey(0)
   cv2.destroyAllWindows()
open_img()

This script is called 'img_mod' and is stored in 'detection'. Now I would like to call this function from another script:

from detection import img_mod
img_mod.open_img()

this creates the following error:

Traceback (most recent call last):
  File "D:/Projects/BJ/Sandbox.py", line 3, in <module>
    img_mod.open_img()
  File "D:\Projects\BJ\detection\img_mod.py", line 6, in open_img
    cv2.imshow('template', template)
cv2.error: OpenCV(3.4.4) C:\projects\opencv-python\opencv\modules\highgui\src\window.cpp:356: error: (-215:Assertion failed) size.width>0 && size.height>0 in function 'cv::imshow'

To me it seems like a cv2 specifit error. But I have no idea, why this doesn't work. Any help would be appreciated.

Answer 1

The error message is related to an assertion failure: size.width>0 && size.height>0

It means the function is not carrying out the action because some conditions are not met.

It is likely your image templates\\\\img_test.jpg is invalid or does not exist. Try, for example, give a full path to a valid image file.

Answer 2

This is what happens when imread() fails to read an image and returns None , and the None gets passed along to imshow() .

There are a few possibilities. The mostly likely is that you're not in the directory you think you are, and there's not a templates folder in the current directory. You can deal with that by passing a full path to img_test.jpg .

Answer 3

Your image is in

D:\Projects\BJ\detection\templates\img_test.jpg

but now you're trying to load it from

D:\Projects\BJ\templates\img_test.jpg

because you run a different Python file.