.. _bounding_rects_circles:


Creating Bounding boxes and circles for contours
*************************************************

Goal
=====

In this tutorial you will learn how to:

.. container:: enumeratevisibleitemswithsquare

   * Use the OpenCV function :bounding_rect:`boundingRect <>`
   * Use the OpenCV function :min_enclosing_circle:`minEnclosingCircle <>`


Theory
======

Code
====

This tutorial code's is shown lines below. You can also download it from `here <https://github.com/Itseez/opencv/tree/master/samples/cpp/tutorial_code/ShapeDescriptors/generalContours_demo1.cpp>`_

.. code-block:: cpp

   #include "opencv2/highgui.hpp"
   #include "opencv2/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, COLOR_BGR2GRAY );
     blur( src_gray, src_gray, Size(3,3) );

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

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

     waitKey(0);
     return(0);
   }

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

     /// Detect edges using Threshold
     threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
     /// Find contours
     findContours( threshold_output, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0) );

     /// Approximate contours to polygons + get bounding rects and circles
     vector<vector<Point> > contours_poly( contours.size() );
     vector<Rect> boundRect( contours.size() );
     vector<Point2f>center( contours.size() );
     vector<float>radius( contours.size() );

     for( int i = 0; i < contours.size(); i++ )
        { approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
          boundRect[i] = boundingRect( Mat(contours_poly[i]) );
          minEnclosingCircle( (Mat)contours_poly[i], center[i], radius[i] );
        }


     /// Draw polygonal contour + bonding rects + circles
     Mat drawing = Mat::zeros( threshold_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_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
          rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
          circle( drawing, center[i], (int)radius[i], color, 2, 8, 0 );
        }

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

Explanation
============

Result
======

#. Here it is:

   ========== ==========
    |BRC_0|   |BRC_1|
   ========== ==========

   .. |BRC_0|  image:: images/Bounding_Rects_Circles_Source_Image.jpg
                    :align: middle

   .. |BRC_1|  image:: images/Bounding_Rects_Circles_Result.jpg
                    :align: middle
