cv2.error: OpenCV(4.7.0) :-1: error: (-5:Bad argument) in function 'imwrite' img data type = 17 is not supported

Question

I'm trying to use a picture to create a Histograms Equalization. I'm imported image and cv2 already but there are still having an issue.

import numpy as np
import cv2 as cv



path = r'C:\Users\Lilly\Downloads\lena_color.jpg'
img = cv.imread(path,0)
equ = cv.equalizeHist(img)
res = np.hstack((img,equ)) 
cv.imwrite('res.png',res)

These is an error.

PS C:\Users\Lilly> & C:/Users/Lilly/AppData/Local/Programs/Python/Python39/python.exe c:/Users/Lilly/Downloads/Equalization.py
Traceback (most recent call last):
  File "c:\Users\Lilly\Downloads\Equalization.py", line 17, in <module>
    cv.imwrite('res.png',res)
cv2.error: OpenCV(4.7.0) :-1: error: (-5:Bad argument) in function 'imwrite'
> Overload resolution failed:
>  - img data type = 17 is not supported
>  - Expected Ptr<cv::UMat> for argument 'img'

Answer 1

imread() failed. It returned None . The file could not be found or the file is corrupt.

equalizeHist() does not complain. It simply returns None too.

res now becomes array([None, None], dtype=object)

imwrite() can't handle this and complains with this error message.

The fix is to make sure imread() succeeds. Figure out if the file actually exists.

assert os.path.exists(path)
img = cv.imread(path)
assert img is not None