c++ - Subtract all contours from image except the one with the largest area -

cv::mat thr;  std::vector<std::vector<cv::point> > contours; std::vector<std::vector<cv::vec4i> > hierarchy;  int largest_area          = 0; int largest_contour_index = 0;  cv::findcontours( thr, contours, hierarchy,cv_retr_ccomp, cv_chain_approx_simple ); // find contours in image  for( int = 0; < contours.size(); i++ )                                           // iterate through each contour. {    double = contourarea( contours[i], false );                                        // find area of contour    if(a > largest_area)    {       largest_area          = a;       largest_contour_index = i;                                                    // store index of largest contour    }  } 

what should after finding index of largest contour? how can delete other contours inner areas? image binary (cv::mat thr). black background white areas. thanks.

in case, deleting contours inner areas equal fill them black. can done drawing contour regions black color:

for (size_t i=0; i<contours.size(); ++i) {     if (i != largest_contour_index) { // not largest 1         cv::drawcontours(thr, contours, i, cv::scalar(0,0,0), cv_filled);     } }