Finding contours in your image — OpenCV 2.4.13.4 documentation

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# Finding contours in your image

## Goal

In this tutorial you will learn how to:

- Use the OpenCV function findContours
- Use the OpenCV function drawContours

## Theory

## Code

This tutorial code’s is shown lines below. You can also download it from here

    #include "opencv2/highgui/highgui.hpp"
    #include "opencv2/imgproc/imgproc.hpp"
    #include <iostream>
    #include <stdio.h>
    #include <stdlib.h>

    using namespace cv;
    using namespace std;

    Mat src; Mat src_gray;
    int thresh = 100;
    int max_thresh = 255;
    RNG rng(12345);

    /// Function header
    void thresh_callback(int, void* );

    /** @function main */
    int main( int argc, char** argv )
    {
      /// Load source image and convert it to gray
      src = imread( argv[1], 1 );

      /// Convert image to gray and blur it
      cvtColor( src, src_gray, CV_BGR2GRAY );
      blur( src_gray, src_gray, Size(3,3) );

      /// Create Window
      char* source_window = "Source";
      namedWindow( source_window, CV_WINDOW_AUTOSIZE );
      imshow( source_window, src );

      createTrackbar( " Canny thresh:", "Source", &thresh, max_thresh, thresh_callback );
      thresh_callback( 0, 0 );

      waitKey(0);
      return(0);
    }

    /** @function thresh_callback */
    void thresh_callback(int, void* )
    {
      Mat canny_output;
      vector<vector<Point> > contours;
      vector<Vec4i> hierarchy;

      /// Detect edges using canny
      Canny( src_gray, canny_output, thresh, thresh*2, 3 );
      /// Find contours
      findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

      /// Draw contours
      Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
      for( int i = 0; i< contours.size(); i++ )
         {
           Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
           drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
         }

      /// Show in a window
      namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
      imshow( "Contours", drawing );
    }

## Explanation

## Result

1. Here it is:

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