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

# -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.

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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)

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.

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import cv2

img = cv2.imread('thumbnail.webp')

img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV)

print(img_hsv)

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

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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)

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

• Warning: can't open/read file: check file path/integrity.

# 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.

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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')

# 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.

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.

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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.

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:

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import cv2

# ...

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

If you are on Linux, use this:

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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.

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pip install scikit-image

pip3 install scikit-image

Now, import and use the module as follows.

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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)

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

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