opencv 轮廓 缺陷检测

1.凸性缺陷
物体与凸壳任何偏差都可以认为是凸性缺陷。
cv.convexityDefects()

import cv2 as cv
import numpy as np
img = cv.imread('star.jpg')
img_gray = cv.cvtColor(img,cv.COLOR_BGR2GRAY)
ret,thresh = cv.threshold(img_gray, 127, 255,0)
im2,contours,hierarchy = cv.findContours(thresh,2,1)
cnt = contours[0]
hull = cv.convexHull(cnt,returnPoints = False)
defects = cv.convexityDefects(cnt,hull)
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])
    cv.line(img,start,end,[0,255,0],2)
    cv.circle(img,far,5,[0,0,255],-1)
cv.imshow('img',img)
cv.waitKey(0)
cv.destroyAllWindows()

2.多边形点测试

dist = cv.pointPolygonTest(cnt,(50,50),True)

3.形状匹配
cv.matchShapes()

import cv2 as cv
import numpy as np
img1 = cv.imread('star.jpg',0)
img2 = cv.imread('star2.jpg',0)
ret, thresh = cv.threshold(img1, 127, 255,0)
ret, thresh2 = cv.threshold(img2, 127, 255,0)
im2,contours,hierarchy = cv.findContours(thresh,2,1)
cnt1 = contours[0]
im2,contours,hierarchy = cv.findContours(thresh2,2,1)
cnt2 = contours[0]
ret = cv.matchShapes(cnt1,cnt2,1,0.0)
print( ret )

参考文献：
https://docs.opencv.org/3.4.3/d5/d45/tutorial_py_contours_more_functions.html
https://blog.csdn.net/qq_41905045/article/details/81536827