samples/cpp/contours2.cpp

An example program illustrates the use of cv::findContours and cv::drawContours

Screenshot of the program

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include <math.h>
#include <iostream>
 
using namespace cv;
using namespace std;
 
static void help(char** argv)
{
 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";
 cout
 << argv[0]
 << "\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, LINE_AA, 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(argv);
 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;
}