opencv中图像有两个或多个连通域，如何寻找最小面积的连通域，并获取该连通域中的坐标呢？

[berlinpand]

现在有一张这样的图像，希望可以找到下面较小段连通域，获取白色区域内的坐标点，还望各位老师指点，谢谢

[shiter]

/// <summary>
/// 回溯法标记连通域
/// </summary>
/// <param name="x">该点的横坐标</param>
/// <param name="y">该点的纵坐标</param>
/// <param name="isMarked">是否已经被标记过，用于记录回溯路线。默认值为false，如果该点已经被标记过，则应指定该参数为true。</param>
        private void Connect(int x, int y, bool isMarked = false)
        {
            if (x == 0 && y == 0) //mat[0, 0]
            {
                if (f(x, y) == 1) mat[x, y] = mark; // new area
            }

            else if (x != 0 && y == 0) // First Row
            {
                if (f(x, y) == 1)
                {
                    if (mat[x - 1, y] != 0)
                    {
                        mat[x, y] = mat[x - 1, y]; // left one
                        Connect(x - 1, y, true);
                    }
                    else
                    {
                        if (isMarked == false)
                            mat[x, y] = ++mark; // new area
                    }
                }
            }

            else if (x == 0 && y != 0) // First Column
            {
                if (f(x, y) == 1)
                {
                    if (mat[x, y - 1] != 0)
                    {
                        mat[x, y] = mat[x, y - 1]; // up one
                        Connect(x, y - 1, true);
                    }
                    else
                    {
                        if (isMarked == false)
                            mat[x, y] = ++mark;
                    }
                }
            }

            else if (x != 0 && y != 0) // other pixel
            {
                if (f(x, y) == 1)
                {
                    if (mat[x, y - 1] == 0 && mat[x - 1, y] == 0) // new area
                    {
                        if (isMarked == false)
                            mat[x, y] = ++mark;
                    }
                    else if (mat[x, y - 1] == 0 && mat[x - 1, y] != 0)
                    {
                        if (isMarked == false)
                            mat[x, y] = mat[x - 1, y];
                        else
                        {
                            if (mat[x - 1, y] > mat[x, y])
                                mat[x - 1, y] = mat[x, y];
                            Connect(x - 1, y, true); // 沿x方向继续回溯
                        }
                    }
                    else if (mat[x, y - 1] != 0 && mat[x - 1, y] == 0)
                    {
                        if (isMarked == false)
                            mat[x, y] = mat[x, y - 1];
                        else
                        {
                            if (mat[x, y - 1] > mat[x, y])
                                mat[x, y - 1] = mat[x, y];
                            Connect(x, y - 1, true); // 沿y方向继续回溯
                        }
                    }
                    else if (mat[x, y - 1] != 0 && mat[x - 1, y] != 0 && mat[x, y - 1] == mat[x - 1, y])
                    {
                        if (isMarked == false)
                            mat[x, y] = mat[x, y - 1];
                        else
                        {
                            if (mat[x, y - 1] > mat[x, y])
                            {
                                mat[x, y - 1] = mat[x - 1, y] = mat[x, y];
                                Connect(x - 1, y, true); // 遇到上边和左边都有已标记像素的情况，两边同时回溯
                                Connect(x, y - 1, true);
                            }
                        }

                    }
                    else if (mat[x, y - 1] != 0 && mat[x - 1, y] != 0 && mat[x, y - 1] != mat[x - 1, y])
                    {
                        mat[x, y] = Math.Min(mat[x - 1, y], mat[x, y - 1]);
                        mat[x - 1, y] = mat[x, y - 1] = mat[x, y]; // 直接消除等价类
                        Connect(x - 1, y, true);
                        Connect(x, y - 1, true);
                    }
                }
            }

[赵4老师]

仅供参考：

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/imgproc/imgproc_c.h"
using namespace std;
using namespace cv;
Mat img,smallImg,gray,bw;
vector<Vec4i> hierarchy;
vector<vector<Point> > contours;
int threshval=128;
Rect r;
Rect maxrect,brect;
int idx,n;
const static Scalar colors[15]={
    CV_RGB(  0,  0,128),
    CV_RGB(  0,128,  0),
    CV_RGB(  0,128,128),
    CV_RGB(128,  0,  0),
    CV_RGB(128,  0,128),
    CV_RGB(128,128,  0),
    CV_RGB(128,128,128),
    CV_RGB(160,160,160),
    CV_RGB(  0,  0,255),
    CV_RGB(  0,255,  0),
    CV_RGB(  0,255,255),
    CV_RGB(255,  0,  0),
    CV_RGB(255,  0,255),
    CV_RGB(255,255,  0),
    CV_RGB(255,255,255),
};
Scalar color;
void gamma_correct(Mat& img, Mat& dst, double gamma) {
	Mat	temp;
	CvMat tmp;

	img.convertTo(temp,	CV_32FC1, 1.0/255.0, 0.0);
	tmp=temp;
	cvPow(&tmp,	&tmp, gamma);
	temp.convertTo(dst , CV_8UC1 , 255.0	, 0.0);
}
int main() {
    cvNamedWindow("display",1);
    img=imread("image.jpg",1);
    r.x=img.cols/10;
    r.y=img.rows/3;
    r.width=img.cols*8/10;
    r.height=img.rows*2/3;
    smallImg=img(r);
    cvtColor(smallImg,gray,CV_BGR2GRAY);
//  medianBlur(gray,gray,5);
    equalizeHist(gray,gray);
    gamma_correct(gray,gray,4.0);
    imshow("display",gray);
    waitKey(0);

	bw=(gray>threshval);
    imshow("display",bw);
    waitKey(0);

	Mat	Structure0=getStructuringElement(MORPH_RECT,Size(3,3));
    erode(bw,bw,Structure0,Point(-1,-1));
	Mat	Structure1=getStructuringElement(MORPH_RECT,Size(6,6));
    dilate(bw,bw,Structure1, Point(-1,-1));
    imshow("display",bw);
    waitKey(0);

    findContours(bw,contours,hierarchy,RETR_EXTERNAL,CHAIN_APPROX_SIMPLE);
    if (!contours.empty()&&!hierarchy.empty()) {
        idx=0;
        n=0;
        vector<Point> approx;
        for (;idx>=0;idx=hierarchy[idx][0]) {
            color=colors[idx%15];
//          drawContours(smallImg,contours,idx,color,1,8,hierarchy);
            approxPolyDP(Mat(contours[idx]), approx, arcLength(Mat(contours[idx]), true)*0.005, true);//0.005为将毛边拉直的系数
            const Point* p = &approx[0];
            int m=(int)approx.size();
            polylines(smallImg, &p, &m, 1, true, color);
            circle(smallImg,Point(p[0].x,p[0].y),3,color);
            circle(smallImg,Point(p[1].x,p[1].y),2,color);
			for	(int i=2;i<m;i++) circle(smallImg,Point(p[i].x,p[i].y),1,color);
            n++;
            if (1==n) {
                maxrect=boundingRect(Mat(contours[idx]));
            } else {
                brect=boundingRect(Mat(contours[idx]));
                CvRect mr(maxrect),br(brect);
                maxrect=cvMaxRect(&mr,&br);
            }
        }
        circle(smallImg,Point(maxrect.x+maxrect.width/2,maxrect.y+maxrect.height/2),2,CV_RGB(255,0,0));
    }
    imshow("display",smallImg);
    waitKey(0);
    cvDestroyWindow("display");
    return 0;
}