OpenCV 3.1 drawContours '(-215) npoints > 0'

Question

I\'m trying to create a mask from a contour, but am getting a C++ error.

Using OS X Yosemite, Python 2.7.10, OpenCV 3.1.0.

def create_mask(img, cnt):
            


        

Answer 1

I think you are adding extra [] around cnt it should be

cv2.drawContours(mask, cnt, 0, (0, 255, 0), -1)

as cnt is already array of array but [cnt] is array of array of arrays which won't work

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Update to the above code

you should convert your contour to numpy array first

ctr = numpy.array(cnt).reshape((-1,1,2)).astype(numpy.int32)
cv2.drawContours(mask, [ctr], 0, (0, 255, 0), -1)

check documentation here

contours is a Python list of all the contours in the image. Each individual contour is a Numpy array of (x,y) coordinates of boundary points of the object.