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samples/cpp/tutorial_code/ShapeDescriptors/generalContours_demo2.cpp

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+/**
+ * @function generalContours_demo2.cpp
+ * @brief Demo code to obtain ellipses and rotated rectangles that contain detected contours
+ * @author OpenCV team
+ */
+
+#include "opencv2/imgcodecs.hpp"
+#include "opencv2/highgui.hpp"
+#include "opencv2/imgproc.hpp"
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+Mat src_gray;
+int thresh = 100;
+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
+    CommandLineParser parser( argc, argv, "{@input | stuff.jpg | input image}" );
+    Mat src = imread( samples::findFile( parser.get<String>( "@input" ) ) );
+    if( src.empty() )
+    {
+        cout << "Could not open or find the image!\n" << endl;
+        cout << "Usage: " << argv[0] << " <Input image>" << endl;
+        return -1;
+    }
+
+    /// Convert image to gray and blur it
+    cvtColor( src, src_gray, COLOR_BGR2GRAY );
+    blur( src_gray, src_gray, Size(3,3) );
+
+    /// Create Window
+    const char* source_window = "Source";
+    namedWindow( source_window );
+    imshow( source_window, src );
+
+    const int max_thresh = 255;
+    createTrackbar( "Canny thresh:", source_window, &thresh, max_thresh, thresh_callback );
+    thresh_callback( 0, 0 );
+
+    waitKey();
+    return 0;
+}
+
+/**
+ * @function thresh_callback
+ */
+void thresh_callback(int, void* )
+{
+    /// Detect edges using Canny
+    Mat canny_output;
+    Canny( src_gray, canny_output, thresh, thresh*2 );
+    /// Find contours
+    vector<vector<Point> > contours;
+    findContours( canny_output, contours, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0) );
+
+    /// Find the rotated rectangles and ellipses for each contour
+    vector<RotatedRect> minRect( contours.size() );
+    vector<RotatedRect> minEllipse( contours.size() );
+    for( size_t i = 0; i < contours.size(); i++ )
+    {
+        minRect[i] = minAreaRect( contours[i] );
+        if( contours[i].size() > 5 )
+        {
+            minEllipse[i] = fitEllipse( contours[i] );
+        }
+    }
+
+    /// Draw contours + rotated rects + ellipses
+    Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
+    for( size_t i = 0; i< contours.size(); i++ )
+    {
+        Scalar color = Scalar( rng.uniform(0, 256), rng.uniform(0,256), rng.uniform(0,256) );
+        // contour
+        drawContours( drawing, contours, (int)i, color );
+        // ellipse
+        ellipse( drawing, minEllipse[i], color, 2 );
+        // 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 );
+        }
+    }
+
+    /// Show in a window
+    imshow( "Contours", drawing );
+}