Skeletonize a single channel opencv image or 2D numpy array

skeletonize.py

def skeletonize(img):
  '''
  Adapted from: 
    https://opencvpython.blogspot.com/2012/05/skeletonization-using-opencv-python.html
  '''
    assert len(img.shape) == 2  #make sure its single channel
    size = np.size(img)
    tenth_size = size/10
    skel = np.zeros(img.shape,np.uint8)

    ret,img = cv2.threshold(img,127,255,0)
    element = cv2.getStructuringElement(cv2.MORPH_CROSS,(3,3))
    done = False

    while( not done):
        eroded = cv2.erode(img,element)
        temp = cv2.dilate(eroded,element)
        temp = cv2.subtract(img,temp)
        skel = cv2.bitwise_or(skel,temp)
        img = eroded.copy()
        zeros = size - cv2.countNonZero(img)
        if zeros==size:
            done = True
    return skel