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samples/cpp/tutorial_code/ImgTrans/CannyDetector_Demo.cpp

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+/**
+ * @file CannyDetector_Demo.cpp
+ * @brief Sample code showing how to detect edges using the Canny Detector
+ * @author OpenCV team
+ */
+
+#include "opencv2/imgproc.hpp"
+#include "opencv2/highgui.hpp"
+#include <iostream>
+
+using namespace cv;
+
+//![variables]
+Mat src, src_gray;
+Mat dst, detected_edges;
+
+int lowThreshold = 0;
+const int max_lowThreshold = 100;
+const int ratio = 3;
+const int kernel_size = 3;
+const char* window_name = "Edge Map";
+//![variables]
+
+/**
+ * @function CannyThreshold
+ * @brief Trackbar callback - Canny thresholds input with a ratio 1:3
+ */
+static void CannyThreshold(int, void*)
+{
+    //![reduce_noise]
+    /// Reduce noise with a kernel 3x3
+    blur( src_gray, detected_edges, Size(3,3) );
+    //![reduce_noise]
+
+    //![canny]
+    /// Canny detector
+    Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );
+    //![canny]
+
+    /// Using Canny's output as a mask, we display our result
+    //![fill]
+    dst = Scalar::all(0);
+    //![fill]
+
+    //![copyto]
+    src.copyTo( dst, detected_edges);
+    //![copyto]
+
+    //![display]
+    imshow( window_name, dst );
+    //![display]
+}
+
+
+/**
+ * @function main
+ */
+int main( int argc, char** argv )
+{
+  //![load]
+  CommandLineParser parser( argc, argv, "{@input | fruits.jpg | input image}" );
+  src = imread( samples::findFile( parser.get<String>( "@input" ) ), IMREAD_COLOR ); // Load an image
+
+  if( src.empty() )
+  {
+    std::cout << "Could not open or find the image!\n" << std::endl;
+    std::cout << "Usage: " << argv[0] << " <Input image>" << std::endl;
+    return -1;
+  }
+  //![load]
+
+  //![create_mat]
+  /// Create a matrix of the same type and size as src (for dst)
+  dst.create( src.size(), src.type() );
+  //![create_mat]
+
+  //![convert_to_gray]
+  cvtColor( src, src_gray, COLOR_BGR2GRAY );
+  //![convert_to_gray]
+
+  //![create_window]
+  namedWindow( window_name, WINDOW_AUTOSIZE );
+  //![create_window]
+
+  //![create_trackbar]
+  /// Create a Trackbar for user to enter threshold
+  createTrackbar( "Min Threshold:", window_name, &lowThreshold, max_lowThreshold, CannyThreshold );
+  //![create_trackbar]
+
+  /// Show the image
+  CannyThreshold(0, 0);
+
+  /// Wait until user exit program by pressing a key
+  waitKey(0);
+
+  return 0;
+}