text: #include "opencv2/imgproc/imgproc.hpp"
  #include "opencv2/highgui/highgui.hpp"
  #include <math.h>
  #include <iostream>
  
  using namespace cv;
  using namespace std;
  
  static void help()
  {
  	cout
  		<< "\nThis program illustrates the use of findContours and drawContours\n"
  		<< "The original image is put up along with the image of drawn contours\n"
  		<< "Usage:\n"
  		<< "./contours2\n"
  		<< "\nA trackbar is put up which controls the contour level from -3 to 3\n"
  		<< endl;
  }
  
  const int w = 500;
  int levels = 3;
  
  vector<vector<Point> > contours;
  vector<Vec4i> hierarchy;
  
  static void on_trackbar(int, void*)
  {
  	Mat cnt_img = Mat::zeros(w, w, CV_8UC3);
  	int _levels = levels - 3;
  	drawContours( cnt_img, contours, _levels <= 0 ? 3 : -1, Scalar(128,255,255),
  			3, 0 , hierarchy, std::abs(_levels) );
  
  	imshow("contours", cnt_img);
  }
  
  int main( int argc, char** argv)
  {
  //	cv::CommandLineParser parser(argc, argv, "{help h||}");
  //	if (parser.has("help"))
  //	{
  //		help();
  //		return 0;
  //	}
  	Mat img = Mat::zeros(w, w, CV_8UC1);
  	//Draw 6 faces
  	for( int i = 0; i < 6; i++ )
  	{
  		int dx = (i%2)*250 - 30;
  		int dy = (i/2)*150;
  		const Scalar white = Scalar(255);
  		const Scalar black = Scalar(0);
  
  		if( i == 0 )
  		{
  			for( int j = 0; j <= 10; j++ )
  			{
  				double angle = (j+5)*CV_PI/21;
  				line(img, Point(cvRound(dx+100+j*10-80*cos(angle)),
  							cvRound(dy+100-90*sin(angle))),
  						Point(cvRound(dx+100+j*10-30*cos(angle)),
  							cvRound(dy+100-30*sin(angle))), white, 1, 8, 0);
  			}
  		}
  
  		ellipse( img, Point(dx+150, dy+100), Size(100,70), 0, 0, 360, white, -1, 8, 0 );
  		ellipse( img, Point(dx+115, dy+70), Size(30,20), 0, 0, 360, black, -1, 8, 0 );
  		ellipse( img, Point(dx+185, dy+70), Size(30,20), 0, 0, 360, black, -1, 8, 0 );
  		ellipse( img, Point(dx+115, dy+70), Size(15,15), 0, 0, 360, white, -1, 8, 0 );
  		ellipse( img, Point(dx+185, dy+70), Size(15,15), 0, 0, 360, white, -1, 8, 0 );
  		ellipse( img, Point(dx+115, dy+70), Size(5,5), 0, 0, 360, black, -1, 8, 0 );
  		ellipse( img, Point(dx+185, dy+70), Size(5,5), 0, 0, 360, black, -1, 8, 0 );
  		ellipse( img, Point(dx+150, dy+100), Size(10,5), 0, 0, 360, black, -1, 8, 0 );
  		ellipse( img, Point(dx+150, dy+150), Size(40,10), 0, 0, 360, black, -1, 8, 0 );
  		ellipse( img, Point(dx+27, dy+100), Size(20,35), 0, 0, 360, white, -1, 8, 0 );
  		ellipse( img, Point(dx+273, dy+100), Size(20,35), 0, 0, 360, white, -1, 8, 0 );
  	}
  	//show the faces
  	namedWindow( "image", 1 );
  	imshow( "image", img );
  	//Extract the contours so that
  	vector<vector<Point> > contours0;
  	findContours( img, contours0, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);
  
  	contours.resize(contours0.size());
  	for( size_t k = 0; k < contours0.size(); k++ )
  		approxPolyDP(Mat(contours0[k]), contours[k], 3, true);
  
  	namedWindow( "contours", 1 );
  	createTrackbar( "levels+3", "contours", &levels, 7, on_trackbar );
  
  	on_trackbar(0,0);
  	waitKey();
  
  	return 0;
  }
  
  