opencv判断轮廓是圆形还是正方形

要判断轮廓是圆形还是正方形，可以用OpenCV中的轮廓近似函数approxPolyDP()来对轮廓进行近似，然后根据近似得到的点数来判断形状。如果点数为4，则为正方形；如果点数为多个，则为圆形。代码示例：

import cv2
import numpy as np

img = cv2.imread('shapes.png')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(gray,127,255,cv2.THRESH_BINARY)
contours,hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

for cnt in contours:
    approx = cv2.approxPolyDP(cnt,0.01*cv2.arcLength(cnt,True),True)
    if len(approx)==4:
        cv2.drawContours(img,[cnt],0,(0,255,0),3)
        cv2.putText(img,'Square',(cnt[0][0][0],cnt[0][0][1]), \
            cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 255, 0), 2, cv2.LINE_AA)
    else:
        cv2.drawContours(img,[cnt],0,(0,0,255),3)
        cv2.putText(img,'Circle',(cnt[0][0][0],cnt[0][0][1]), \
            cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 0, 255), 2, cv2.LINE_AA)

cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()