CODEWITHSUNDEEP
python-3.xopencv3.0
Riker
Riker

Reputation: 85

OpenCV polylines throws assertion failure even when arg type is what it's supposed to be

Several threads report this problem, but all of them show fixing the type of the point list (to int32, i.e. CV_32S) as the solution. The point list below has the appropriate type.

>>> ti = np.zeros((400,400,3), np.uint8)                # Test image
>>> mask = np.array([[213,60],[333,240],[93,240],[150,120]], np.int32)  # Test point list
>>> cv2.polylines(ti, mask, True, (255,0,0), 1)
*** cv2.error: OpenCV(3.4.3) C:\projects\opencv-python\opencv\modules\imgproc\src\drawing.cpp:2437: error: (-215:Assertion failed) p.checkVector(2, CV_32S) >= 0 in function 'cv::polylines'

>>> print(mask.dtype, mask.shape)
int32 (4, 2)

I've tried changing the type (I get a different error, complains it's the wrong type) and re-casting it to int32. Can't make it play nice...

fillConvexPoly works fine (which got me what I needed for now), fillPoly exhibits the same problem as above.

Upvotes: 0

Views: 2571

Answers (1)

I.Newton
I.Newton

Reputation: 1783

Correction to the above is - 

cv2.polylines(ti, [mask], True, (255,0,0), 1)

Upvotes: 4

Related Questions