-215:Assertion failed !_src.empty() in function 'cvtColor'

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Borislav Hadzhiev

Last updated: Aug 27, 2023
4 min

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# -215:Assertion failed !_src.empty() in function 'cvtColor'

The Python OpenCV error "(-215:Assertion failed) !_src.empty() in function 'cvtColor'" occurs when the image you passed to cv2.cvtColor() didn't load correctly and was empty.

Make sure the image path you passed to cv2.imread() exists and the image at the path is not empty.

Here is an example of how the error occurs.

main.py
import cv2 img = cv2.imread('thumbnail123.webp') print(img) # 👉️ None img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV) # ⛔️ cv2.error: OpenCV(4.8.0) /io/opencv/modules/imgproc/src/color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor' print(img_hsv)

assertion failed src empty in function cvt color

The error in the example is caused because the path we passed to cv2.imread() doesn't point to an image that exists and is not empty.

If I replace the path with this of a valid image that exists, everything works as expected.

main.py
import cv2 img = cv2.imread('thumbnail.webp') img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV) print(img_hsv)

make sure image exists and is not empty

If you need to check if the specified path exists, use the os.path.exists method.

main.py
import os import cv2 img_path = 'thumbnail123.webp' if os.path.exists(img_path): img = cv2.imread(img_path) img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV) print(img_hsv) else: print('Path does NOT exist', img_path)

checking if path exists

If you're running into issues when specifying the path in the call to csv.imread(), check out the following article:

# The !_src.empty() error message means that the image frame is empty

The !_src.empty() error message means that the image frame is empty.

Therefore, you can't pass an empty frame to the cv2.cvtColor() method.

You can use an if statement to check if the image frame is not None.

main.py
import cv2 img_path = 'thumbnail123.webp' img = cv2.imread(img_path) if img is not None: img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV) print(img_hsv) else: print('Image frame is empty')

checking if image frame is not none

# Running into issues when reading a frame from a Webcam

If you're getting the error when reading a frame from a webcam, make sure the webcam is not being used by another program.

If your webcam is used by another program, the frame will likely be empty, resulting in the error.

You can end the other task that uses your cam (e.g. Zoom, Skype, Google Hangouts etc.) and rerun your Python script to solve the error.

If that didn't help and the error is caused when reading a frame from a webcam, make sure your webcam drivers are up-to-date.

If you're grabbing the image data from a camera, make sure the camera connection hasn't failed and the camera is configured correctly.

# Try to use a raw string for the path

If that didn't help, try to specify the path using a raw string.

For example, on Windows, it might look something like this.

main.py
import cv2 img_path_windows = r'C:\Users\YourUser\Desktop\your-image.png' print(img_path_windows)

Strings that are prefixed with r are called raw strings and treat backslashes as literal characters.

If prefixing the string with r didn't help, make sure the image's extension is specified in the file path and is correct.

The path to the image should also not contain special characters or umlauts.

Also, if you're only specifying an image name when calling cv2.imread() make sure your terminal is located in the same directory as the image and the Python script.

If you're calling the cv2.VideoCapture() method, pass it 0 on Windows or -1 on Linux as a parameter.

For example, on Windows, use this:

main.py
import cv2 # ... # ✅ Correct for Windows cap = cv2.VideoCapture(0)

If you are on Linux, use this:

main.py
import cv2 # ... # ✅ Correct for Linux cap = cv2.VideoCapture(-1)

# Try using skimage.io.imread() instead of cv2.imread()

Another thing you can try is to use the skimage.io.imread() method instead of cv2.imread().

First, install the scikit-image module by running the following command.

shell
pip install scikit-image pip3 install scikit-image

Now, import and use the module as follows.

main.py
import cv2 from skimage import io img_path = 'thumbnail.webp' img = io.imread(img_path) img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV) print(img_hsv)

using skimage io imread instead of cv2 imread

You can pass the img object that is returned from skimage.io.imread() to the cv2.cvtColor() method.

# Make sure you aren't running into permission issues

Make sure you aren't running into permission issues and the image file is accessible from your current user.

For example, you might've blocked your camera from accessing applications.

If you get the message: Warning: can't open/read file: check file path/integrity, click on the link and follow the instructions.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

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