如何使 cv2.imread() 不为空？

Question

The part of my code that I am having trouble on is the following.

if __name__ == '__main__':
    for n, image_file in enumerate(os.scandir(image_folder)):
        img = image_file
        fig, ax = plt.subplots(1)
#       mngr = plt.get_current_fig_manager()
#       mngr.window.setGeometry(250, 120, 1280, 1024)
        image = cv2.imread(image_file.path)
        image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)

I receive the following error

 image = cv2.cvtColor(image,cv2.COLOR_BGR2RGB)
    cv2.error: OpenCV(3.4.4) C:\projects\opencv-python\opencv\module\imgproc\src\color.cpp:181:error:(-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

I understand that the imread() may be empty because the images it is trying to read are not correctly saved. I am trying to test this code with 3 images saved as 000001, 000002, 000003... I am confused on why the images that are saved in the folder in C:\\imagez are not working. I have tried saving 3 new images and still get the same error. Any advise would be great!

Answer 1

If you read the documentation on cv2.imread() you can see that it may fail - in that case it returns None (thats what Mat::data==NULL translates to in python):

The function imread loads an image from the specified file and returns it. If the image cannot be read (because of missing file, improper permissions, unsupported or invalid format), the function returns an empty matrix ( Mat::data==NULL ).

If you feed None as input to cv2.cvtColor(image, cv2.COLOR_BGR2RGB) - it will raise an error on checking the argument (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor' and finding it to be None :

Fix:

if __name__ == '__main__':
    for n, image_file in enumerate(os.scandir(image_folder)):
        fig, ax = plt.subplots(1)
        image = cv2.imread(image_file.path)
        if image:
            image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
        else:
            print("Unable to load image at path {}".format(image_file))

Check the _exact_spelling of your paths that give you these problems - it may be simply a typo in your path/filename.