opencv bone extraction

The principle refers to this blog https://blog.csdn.net/hjxu2016/article/details/80737696

code show as below:

import cv2
import numpy as np

im=cv2.imread('1.png',cv2.IMREAD_GRAYSCALE)
thresh,im=cv2.threshold(im,0,255,cv2.THRESH_BINARY+cv2.THRESH_OTSU)
cv2.imshow('binary.png',im)#控制背景为黑色
dst = im.copy()

num_erode = 0

while(True):
    if np.sum(dst)==0:
        break
    kernel = cv2.getStructuringElement(cv2.MORPH_CROSS,(3,3))
    dst = cv2.erode(dst,kernel)
    num_erode = num_erode + 1

skeleton = np.zeros(dst.shape,np.uint8)

for x in range(num_erode):
    kernel = cv2.getStructuringElement(cv2.MORPH_CROSS,(3,3))
    dst = cv2.erode(im,kernel,None,None,x)
    open_dst = cv2.morphologyEx(dst,cv2.MORPH_OPEN,kernel)
    result = dst - open_dst
    skeleton = skeleton + result
    cv2.waitKey(1000)


cv2.imshow('result',skeleton)

cv2.waitKey(0)
cv2.destroyAllWindows()

Use rect as a structural element: