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You can use morphological operators like erode dilate or closing opening.

If you want to draw hole in your surface you have to use RETR_TREE insted of CV_RETR_EXTERNAL in findContours

You can use morphological operators like erode dilate or closing opening.

If you want to draw hole in your surface you have to use RETR_TREE insted of CV_RETR_EXTERNAL in findContours

0 = [-1, -1, 1, -1] // contour 0 :-1 no next contour,-1  no previous contour, 1 contour #1 is a child, -1 no parent contour  
1 = [3, -1, 2, 0]  // contour 1 :-3 next contour,-1  no previous contour, 1 contour #2 is a child, 0 is parent contour  
2 = [-1, -1, -1, 1]
3 = [-1, 1, -1, 0]

You can use morphological operators like erode dilate or closing opening.

If you want to draw hole in your surface you have to use RETR_TREE insted of CV_RETR_EXTERNAL in findContours

About hierarchy : Original image is :

Contourr with hiereachy are

0 = [-1, -1, 1, -1] // contour 0 :-1 no next contour,-1  no previous contour, 1 contour #1 is a child, -1 no parent contour  
1 = [3, -1, 2, 0]  // contour 1 :-3 next contour,-1  no previous contour, 1 contour #2 is a child, 0 is parent contour  
2 = [-1, -1, -1, 1]
3 = [-1, 1, -1, 0]

Mat img = imread("C:/Users/Laurent.PC-LAURENT-VISI/Desktop/14887743804853655.jpg", CV_LOAD_IMAGE_GRAYSCALE);
imshow("original", img);
Mat y;
threshold(img, y, 50, 255, THRESH_BINARY);
imshow("threshold", y);
double ccMin, ccMax;
findContours(y, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);
Mat c = Mat::zeros(img.size(), CV_8U);
for (int i = 0; i <contours.size(); i++)
{
    cout<<i<<" = "<<hierarchy[i]<<"\n";
}
for (int i = 0; i <contours.size(); i++)
{
    drawContours(c, contours, i, Scalar(255), 1, LINE_8, hierarchy, 0);
    putText(c,format("%d",i),contours[i][0], FONT_HERSHEY_SIMPLEX,0.5,Scalar(255));
}
imshow("ctr",c);
imwrite("c.png",c);
waitKey(0);

You can use morphological operators like erode dilate or closing opening.

If you want to draw hole in your surface you have to use RETR_TREE insted instead of CV_RETR_EXTERNAL in findContours

About hierarchy : Original image is :

Contourr Contours with hiereachy hierarchy are

0 = [-1, -1, 1, -1] // contour 0 :-1 no next contour,-1  no previous contour, 1 contour #1 is a child, -1 no parent contour  
1 = [3, -1, 2, 0]  // contour 1 :-3 next contour,-1  no previous contour, 1 contour #2 is a child, 0 is parent contour  
2 = [-1, -1, -1, 1]
3 = [-1, 1, -1, 0]

program is :

Mat img = imread("C:/Users/Laurent.PC-LAURENT-VISI/Desktop/14887743804853655.jpg", CV_LOAD_IMAGE_GRAYSCALE);
imshow("original", img);
Mat y;
threshold(img, y, 50, 255, THRESH_BINARY);
imshow("threshold", y);
double ccMin, ccMax;
findContours(y, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);
Mat c = Mat::zeros(img.size(), CV_8U);
for (int i = 0; i <contours.size(); i++)
{
    cout<<i<<" = "<<hierarchy[i]<<"\n";
}
for (int i = 0; i <contours.size(); i++)
{
    drawContours(c, contours, i, Scalar(255), 1, LINE_8, hierarchy, 0);
    putText(c,format("%d",i),contours[i][0], FONT_HERSHEY_SIMPLEX,0.5,Scalar(255));
}
imshow("ctr",c);
imwrite("c.png",c);
waitKey(0);