Opencv Python：contours.cpp：1969：错误：（-215）ptnum＆gt; 3在函数凸性缺陷中

Question

当我试图获得凸性缺陷时，我不断收到此错误：contours.cpp：1969：error：（ - 1515）ptnum＆gt; 3在函数凸性缺陷中。我尝试过很多不同的东西，但似乎没什么用。我觉得我做凸性缺陷的方式是错误的。如果有人能用适当的方式向我展示非常有用的代码。

贝娄是我的代码：

import cv2
import numpy as np

cap = cv2.VideoCapture(0)

while(1):

   _, frame = cap.read()
   hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

   # define range of green color in HSV
   lower_green = np.array([50,100,100], dtype=np.uint8)
   upper_green = np.array([70,255,255], dtype=np.uint8)

   # Threshold the HSV image to get only green colors
   mask = cv2.inRange(hsv, lower_green, upper_green)
   contours,hierarchy = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
   #cnt = contours[0]
   cv2.drawContours(frame, contours, -1, (255,0,0), 3)

   #cnt = 0
   for cnt in contours:
       hull = cv2.convexHull(cnt,returnPoints=False)
       if (len(hull)>=3):
           defects = cv2.convexityDefects(cnt,hull)
           if (defects != None):
               for i in range(defects.shape[0]):
                   s,e,f,d = defects[i,0]
                   start = tuple(cnt[s][0])
                   end = tuple(cnt[e][0])
                   far = tuple(cnt[f][0])
                   cv2.line(frame,start,end,[0,255,0],2)
                   cv2.circle(frame,far,5,[0,0,255],-1)

   res = cv2.bitwise_and(frame,frame, mask= mask)

   cv2.imshow('frame',frame)
   cv2.imshow('mask',mask)
   cv2.imshow('res',res)

   k = cv2.waitKey(5) & 0xFF
   if k == 27:
       break

cv2.destroyAllWindows()