.. _bounding_rotated_ellipses:


为轮廓创建可倾斜的边界框和椭圆
**********************************************************

目标
=====

在这个教程中你将学习到如何:

.. container:: enumeratevisibleitemswithsquare

   * 使用OpenCV函数 :min_area_rect:`minAreaRect <>` 
   * 使用OpenCV函数 :fit_ellipse:`fitEllipse <>`
           

原理
======

例程
====

例程的代码在下面显示. 你也可以从 `这里 <https://code.ros.org/svn/opencv/trunk/opencv/samples/cpp/tutorial_code/ShapeDescriptors/generalContours_demo2.cpp>`_ 下载

.. code-block:: cpp 

   #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 )
   {
     /// 加载源图像
     src = imread( argv[1], 1 );

     /// 转为灰度图并模糊化
     cvtColor( src, src_gray, CV_BGR2GRAY );
     blur( src_gray, src_gray, Size(3,3) );

     /// 创建窗体
     char* source_window = "Source";
     namedWindow( source_window, CV_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;

     /// 阈值化检测边界
     threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
     /// 寻找轮廓  
     findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

     /// 对每个找到的轮廓创建可倾斜的边界框和椭圆
     vector<RotatedRect> minRect( contours.size() );
     vector<RotatedRect> minEllipse( contours.size() );

     for( int i = 0; i < contours.size(); i++ )
        { minRect[i] = minAreaRect( Mat(contours[i]) ); 
          if( contours[i].size() > 5 )
            { minEllipse[i] = fitEllipse( Mat(contours[i]) ); }
        } 

     /// 绘出轮廓及其可倾斜的边界框和边界椭圆
     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) );
          // contour
          drawContours( drawing, contours, i, color, 1, 8, vector<Vec4i>(), 0, Point() ); 
          // ellipse
          ellipse( drawing, minEllipse[i], color, 2, 8 );
          // rotated rectangle        
          Point2f rect_points[4]; minRect[i].points( rect_points );
          for( int j = 0; j < 4; j++ )
             line( drawing, rect_points[j], rect_points[(j+1)%4], color, 1, 8 ); 
        }

     /// 结果在窗体中显示
     namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
     imshow( "Contours", drawing ); 
   }

说明
============

结果
======

#. 结果如下图:

   ========== ==========  
    |BRE_0|   |BRE_1|   
   ========== ==========   

   .. |BRE_0|  image:: images/Bounding_Rotated_Ellipses_Source_Image.jpg
                    :align: middle

   .. |BRE_1|  image:: images/Bounding_Rotated_Ellipses_Result.jpg
                    :align: middle   

翻译者
=================
zhlifly@ `OpenCV中文网站 <http://www.opencv.org.cn>`_  <zhlifly@gmail.com>