OpenCV如何在C++中从网络摄像头(跟踪）绘制2个最大对象的轮廓

有人能帮我解决这个问题吗？我需要用相同的颜色从两个最大的物体上绘制轮廓，但我总是会出错，这是我的代码。

void showconvex(Mat &thresh,Mat &frame)
{
    int largest_index = 0;
    int largest_contour = 0;
    int second_largest_index = 0;
    int second_largest_contour = 0;
    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;
    //find contours
    findContours(thresh, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE);
    /// Find the convex hull object for each contour
    vector<vector<Point> >hull(contours.size());
    vector<vector<int> >inthull(contours.size());
    vector<vector<Vec4i> >defects(contours.size());
    for (int i = 0; i < contours.size(); i++)
    {
        convexHull(Mat(contours[i]), hull[i], false);
        convexHull(Mat(contours[i]),inthull[i], false);
        if (inthull[i].size()>3)
            convexityDefects(contours[i], inthull[i], defects[i]);
    }
    //find largest contour
    for (int i = 0; i< contours.size(); i++) // iterate through each contour. 
    {
        double a = contourArea(contours[i].size());  //  Find the area of contour
        if (a>largest_contour)
        {
            second_largest_contour = largest_contour;
            second_largest_index = largest_index;
            largest_contour = a;
            largest_index = i;                
        }
        else if(contours[i].size() > second_largest_contour)
        {
            second_largest_contour = contours[i].size();
            second_largest_index = i;
        }
    }
    drawContours(frame, contours, largest_index, CV_RGB(0,255,0), 2, 8, hierarchy);
    drawContours(frame, contours, second_largest_index, CV_RGB(0,255,0), 2, 8, hierarchy);
}