python opencv error in Emacs when running cv2.Canny()

Question

I encountered a very strange issue when using OpenCV's cv2.Canny() function in the python shell in Emacs. When I run cv2.Canny(img, thresh1, thresh2), I got error message

OpenCV Error: Assertion failed (depth == CV_8U) in cv::Canny, file D:\Build\OpenCV\opencv-3.2.0\modules\imgproc\src\canny.cpp, line 845 Traceback (most recent call last): File "", line 1, in File "../myscript.py", line 34, in lines = cv2.HoughLines(edges,1,np.pi/180,200) cv2.error: D:\Build\OpenCV\opencv-3.2.0\modules\imgproc\src\canny.cpp:845: error: (-215) depth == CV_8U in function cv::Canny

I don't even have a D drive on my computer, and why the source code has issue with this? it should already been compiled..

I haven't observe any other functions in python-opencv cause this issue. I also tried to install different versions, and same error for this particular function call, but the line number varies because the canny.cpp file is of different versions.

However, everything is fine, when I run the same line in System Python Shell...

my system environment:

windows7 64bit
python 3.5
python-opencv: 3.1, or 3.2
emacs 25.1.1

Your img needs to be casted as an uint8. CV_8U. Import numpy and add the following line after you load your image img= np.uint8(img). Use cv2.Canny after. — Zroq
– Zroq, Commented Feb 22, 2017 at 22:35

dspencer · Accepted Answer · 2020-04-22 16:13:52Z

9

The issue is that your image (or one of your images) is not in 8 bit format (8 bit format means each of three channels is in [0,255]).

You can change this by adding:

img = img.astype(np.uint8)

before you call cv2.Canny.

edited Apr 22, 2020 at 16:13

dspencer

4,5014 gold badges25 silver badges46 bronze badges

answered Mar 21, 2018 at 21:09

Megan Hardy

3974 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

python opencv error in Emacs when running cv2.Canny()

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related