我试图创建一个面具从轮廓，但我得到一个C++错误.
使用OS X约塞米蒂，Python 2.7.10，OpenCV 3.1.0.

def create_mask(img, cnt):
    '''Create a mask of the same size as the image
       based on the interior of the contour.'''
    mask = np.zeros((img.shape[0], img.shape[1]), np.uint8)
    print("create_mask, cnt=%s" % cnt)
    cv2.drawContours(mask, [cnt], 0, (0, 255, 0), -1)
    return mask

print("Creating mask from contour %s, on raw shape %s" % (page_contour, raw.shape))
page_mask = create_mask(raw, page_contour)

输出（错误见底部）：

Creating mask from contour [[ 1626.   360.]
 [ 1776.  3108.]
 [  126.  3048.]
 [  330.   486.]], on raw shape (3840, 2160, 3)
create_mask, cnt=[[ 1626.   360.]
 [ 1776.  3108.]
 [  126.  3048.]
 [  330.   486.]]
OpenCV Error: Assertion failed (npoints > 0) in drawContours, file /tmp/opencv320160309-92782-1efch74/opencv-3.1.0/modules/imgproc/src/drawing.cpp, line 2380
Traceback (most recent call last):
  File "./books.py", line 209, in <module>
    page_mask = create_mask(raw, page_contour)
  File "./books.py", line 123, in create_mask
    cv2.drawContours(mask, [cnt], 0, (0, 255, 0), -1)
cv2.error: /tmp/opencv320160309-92782-1efch74/opencv-3.1.0/modules/imgproc/src/drawing.cpp:2380: error: (-215) npoints > 0 in function drawContours

文档说它应该得到一个数组的数组，这似乎是我给它的。怎么了？
代码从OpenCV 2移植。x.