OpenCV  4.1.2
Open Source Computer Vision
samples/cpp/contours2.cpp

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

Screenshot of the program
#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, 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();
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);
return 0;
}
cv::sin
softdouble sin(const softdouble &a)
Sine.
cv::Mat::zeros
static MatExpr zeros(int rows, int cols, int type)
Returns a zero array of the specified size and type.
cv::waitKey
int waitKey(int delay=0)
Waits for a pressed key.
highgui.hpp
cv::namedWindow
void namedWindow(const String &winname, int flags=WINDOW_AUTOSIZE)
Creates a window.
cv::Scalar_< double >
cv::findContours
void findContours(InputArray image, OutputArrayOfArrays contours, OutputArray hierarchy, int mode, int method, Point offset=Point())
Finds contours in a binary image.
cv::Size
Size2i Size
Definition: types.hpp:347
cv::line
void line(InputOutputArray img, Point pt1, Point pt2, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a line segment connecting two points.
CV_8UC3
#define CV_8UC3
Definition: interface.h:90
cv::cos
softdouble cos(const softdouble &a)
Cosine.
cv::abs
static uchar abs(uchar a)
Definition: cvstd.hpp:66
cvRound
int cvRound(double value)
Rounds floating-point number to the nearest integer.
Definition: fast_math.hpp:197
cv::imshow
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
cv::approxPolyDP
void approxPolyDP(InputArray curve, OutputArray approxCurve, double epsilon, bool closed)
Approximates a polygonal curve(s) with the specified precision.
cv::Scalar
Scalar_< double > Scalar
Definition: types.hpp:669
cv::drawContours
void drawContours(InputOutputArray image, InputArrayOfArrays contours, int contourIdx, const Scalar &color, int thickness=1, int lineType=LINE_8, InputArray hierarchy=noArray(), int maxLevel=INT_MAX, Point offset=Point())
Draws contours outlines or filled contours.
cv::Point
Point2i Point
Definition: types.hpp:194
cv::Mat
n-dimensional dense array class
Definition: mat.hpp:791
cv::CommandLineParser
Designed for command line parsing.
Definition: utility.hpp:831
CV_8UC1
#define CV_8UC1
Definition: interface.h:88
cv::createTrackbar
int createTrackbar(const String &trackbarname, const String &winname, int *value, int count, TrackbarCallback onChange=0, void *userdata=0)
Creates a trackbar and attaches it to the specified window.
cv
"black box" representation of the file storage associated with a file on disk.
Definition: affine.hpp:51
imgproc.hpp
CV_PI
#define CV_PI
Definition: cvdef.h:320
cv::CHAIN_APPROX_SIMPLE
Definition: imgproc.hpp:432
cv::RETR_TREE
Definition: imgproc.hpp:420
cv::ellipse
void ellipse(InputOutputArray img, Point center, Size axes, double angle, double startAngle, double endAngle, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a simple or thick elliptic arc or fills an ellipse sector.
cv::LINE_AA
antialiased line
Definition: imgproc.hpp:805