Extend

import cv2
import numpy as np
o=cv2.imread('C:/Users/xpp/Desktop/coins.png')#原始图像
cv2.imshow("original",o)
gray=cv2.cvtColor(o,cv2.COLOR_BGR2GRAY)#将彩色图片转换为灰度图片
ret,binary=cv2.threshold(gray,127,255,cv2.THRESH_BINARY)#将灰度图片转换为二值图片
contours,hierarchy=cv2.findContours(binary,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)#计算图像轮廓
n=len(contours)
contoursImg=[]
for i in range(n):
    temp=np.zeros(o.shape,np.uint8)
    contoursImg.append(temp)
x,y,w,h=cv2.boundingRect(contours[i])#计算矩形包围框
cv2.drawContours(o,contours[i],-1,(0,0,255),3)#绘制图像轮廓
cv2.rectangle(o,(x, y),(x+w,y+h),(255,255,255),3)#(x,y)是矩形顶点，(x+w,y+h)是对角顶点，(255,255,255)是灰度级，3矩形边线宽度
rectArea=w*h#计算矩形边界面积
cntArea=cv2.contourArea(contours[i])#计算轮廓面积
extend=float(cntArea)/rectArea#计算Extend
print(extend)
cv2.imshow("result",o)
cv2.waitKey()
cv2.destroyAllWindows()