Скачать или смотреть How to Fix the OpenCV Image Write Error: (-215:Assertion failed) !_img.empty()

Learn how to resolve the OpenCV error related to image writing and ensure your image cropping is done correctly.
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Understanding and Resolving the OpenCV Image Write Error

If you are working with Python and OpenCV, you might encounter the perplexing error message related to image writing: (-215:Assertion failed) !_img.empty(). This can be especially frustrating for beginners who are trying to manipulate images. In this guide, we'll break down the problem and provide a straightforward solution.

The Problem: Error Explained

When you try to use the cv2.imwrite() function to save an image, OpenCV expects that the image you are trying to write is not empty. The error you see generally indicates that the image variable you're attempting to save has not been loaded correctly or is empty.

Common Causes of the Error

File Not Found: The specified path for the image does not point to an existing file.

Incorrect Image Manipulation: If you attempt to crop an image with dimensions that exceed the original image size, it can lead to an empty output.

Read Issues: Any issues while reading the image file may result in the image variable being empty.

In the code you provided, the exact line producing this error is buried within the image cropping section.

Solution: Fixing the Code

Step-by-Step Diagnosis and Fix

Check Image Loading:
Make sure that the images you want to process exist in the specified directory ("./image_frames/frame" + str(a) + ".png"). A quick way to check if the image is loaded is to print the image variable after the cv2.imread() function.

[[See Video to Reveal this Text or Code Snippet]]

Validating Crop Dimensions:
Once you've confirmed that your images are loaded properly, the next step is to ensure that the cropping dimensions make sense. In your original code, the crop was defined as:

[[See Video to Reveal this Text or Code Snippet]]

However, it's possible that the original image does not have sufficient height or width, leading to empty output. To fix this, adjust the crop to fit within the dimensions of the source image.

Here’s an example of a revised crop dimensions:

[[See Video to Reveal this Text or Code Snippet]]

Re-run the Code:
After making the adjustments, run the code again to see if the error persists. If all goes well, your cropped images should now save without errors.

Example Revised Code

Here's how your final script should look:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Error handling is a crucial aspect of coding, especially when working with external files such as images. By validating your image loading and ensuring the cropping dimensions are correct, you can avoid the frustrating (-215:Assertion failed) !_img.empty() error in OpenCV.

Stay curious and keep experimenting with OpenCV – you'll only get better with practice!