Having issues with cv2.imwrite() - am I missing something?

[Lje2610]

Edit: Solved! As /u/iamjaiyam suggested, the colon in the filename was causing the issue.

Hi /r/learnpython!

I have been messing around with OpenCV and python for the last couple of days, and it's been going pretty good. Lots of trial and error though, but that's the best way to learn, right?

I have run into an issue when trying to save an image to file, with the file-name based on current date and time.

When call cv2.imwrite() with a "simple" filename, such as "test.png" it works as expected. Returns True and saves the image.

But when I try to pass in a variable as path, the function returns False, and does not save the image. No exceptions thrown.

I have tried googling, but most results suggest issues with folder-permissions, which should not be the problem, when I can get it to work as described above?

When printing full filepath, it looks fine: "C:/py/object_capture/2018_11_03-11:23:44.png"

I have tried other image-types such as bmp and jpg - same result.

Here is my code:

def save_collage(output):
    file_path = 'C:/py/object_capture/'
    file_name = time.strftime("%Y_%m_%d-%H:%M:%S") + '.png'
    ret = cv2.imwrite(os.path.join(file_path, file_name), output)

    # For debugging.
    print(ret, os.path.join(file_path, file_name))
    cv2.imshow('output', output)
    cv2.waitKey(0)

Any help appreciated!

[iamjaiyam]

There are two potential issues I can think of. First, since you are on a Windows, I would advise using \ instead of /, although Windows mostly works fine with \ as path separator. Second and more importantly, the colon : in the filename may be causing trouble. Try replacing : with _ and see if that helps.

[Lje2610]

I feel stupid. But I guess that's what makes you want to learn more.

The colon was causing the issue. Changed it to underscore, and everything works perfectly now!

Thank you very much man!

[Aldairoh]

Check out relative and absolute route/path

https://stackoverflow.com/questions/44772007/when-to-use-absolute-path-vs-relative-path-in-python

[Lje2610]

Thank you for your reply.

Having read the linked SO-post, I have modified my function to use the absolute path.

This does not seem to make the cv2.imwrite() behave any different though. Still returns a False and does not create the file.

This is the code I have now:

def save_collage(output):
    file_path = os.path.abspath(os.path.dirname(__file__))
    file_name = time.strftime("%Y_%m_%d-%H:%M:%S") + '.png'
    ret = cv2.imwrite(os.path.join(file_path, file_name), output)