opencv3计算图像中轮廓的面积

#include<iostream>
#include<opencv2/opencv.hpp>
#include<vector>

using namespace cv;
using namespace std;

int main()
{
	Mat srcImage = imread("group.jpg");
	imshow("【原图】", srcImage);

	//首先对图像进行空间的转换
	Mat grayImage;
	cvtColor(srcImage, grayImage, CV_BGR2GRAY);
	//对灰度图进行滤波
	GaussianBlur(grayImage, grayImage, Size(3, 3), 0, 0);
	imshow("【滤波后的图像】", grayImage);

	//为了得到二值图像，对灰度图进行边缘检测
	Mat cannyImage;
	Canny(grayImage, cannyImage, 128, 255, 3);
	//在得到的二值图像中寻找轮廓
	vector<vector<Point>> contours;
	vector<Vec4i> hierarchy;
	findContours(cannyImage, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));

	//绘制轮廓
	for (int i = 0; i < (int)contours.size(); i++)
	{
		drawContours(cannyImage, contours, i, Scalar(255), 1, 8);
	}
	imshow("【处理后的图像】", cannyImage);

	//计算轮廓的面积
	for (int i = 0; i < (int)contours.size(); i++)
	{
		double g_dConArea =