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samples/cpp/tutorial_code/Histograms_Matching/calcBackProject_Demo1.cpp

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+/**
+ * @file BackProject_Demo1.cpp
+ * @brief Sample code for backproject function usage
+ * @author OpenCV team
+ */
+
+#include "opencv2/imgproc.hpp"
+#include "opencv2/imgcodecs.hpp"
+#include "opencv2/highgui.hpp"
+
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+/// Global Variables
+Mat hue;
+int bins = 25;
+
+/// Function Headers
+void Hist_and_Backproj(int, void* );
+
+/**
+ * @function main
+ */
+int main( int argc, char* argv[] )
+{
+    //! [Read the image]
+    CommandLineParser parser( argc, argv, "{@input |  | input image}" );
+    Mat src = imread( 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;
+    }
+    //! [Read the image]
+
+    //! [Transform it to HSV]
+    Mat hsv;
+    cvtColor( src, hsv, COLOR_BGR2HSV );
+    //! [Transform it to HSV]
+
+    //! [Use only the Hue value]
+    hue.create(hsv.size(), hsv.depth());
+    int ch[] = { 0, 0 };
+    mixChannels( &hsv, 1, &hue, 1, ch, 1 );
+    //! [Use only the Hue value]
+
+    //! [Create Trackbar to enter the number of bins]
+    const char* window_image = "Source image";
+    namedWindow( window_image );
+    createTrackbar("* Hue  bins: ", window_image, &bins, 180, Hist_and_Backproj );
+    Hist_and_Backproj(0, 0);
+    //! [Create Trackbar to enter the number of bins]
+
+    //! [Show the image]
+    imshow( window_image, src );
+    // Wait until user exits the program
+    waitKey();
+    //! [Show the image]
+
+    return 0;
+}
+
+/**
+ * @function Hist_and_Backproj
+ * @brief Callback to Trackbar
+ */
+void Hist_and_Backproj(int, void* )
+{
+    //! [initialize]
+    int histSize = MAX( bins, 2 );
+    float hue_range[] = { 0, 180 };
+    const float* ranges = { hue_range };
+    //! [initialize]
+
+    //! [Get the Histogram and normalize it]
+    Mat hist;
+    calcHist( &hue, 1, 0, Mat(), hist, 1, &histSize, &ranges, true, false );
+    normalize( hist, hist, 0, 255, NORM_MINMAX, -1, Mat() );
+    //! [Get the Histogram and normalize it]
+
+    //! [Get Backprojection]
+    Mat backproj;
+    calcBackProject( &hue, 1, 0, hist, backproj, &ranges, 1, true );
+    //! [Get Backprojection]
+
+    //! [Draw the backproj]
+    imshow( "BackProj", backproj );
+    //! [Draw the backproj]
+
+    //! [Draw the histogram]
+    int w = 400, h = 400;
+    int bin_w = cvRound( (double) w / histSize );
+    Mat histImg = Mat::zeros( h, w, CV_8UC3 );
+
+    for (int i = 0; i < bins; i++)
+    {
+        rectangle( histImg, Point( i*bin_w, h ), Point( (i+1)*bin_w, h - cvRound( hist.at<float>(i)*h/255.0 ) ),
+                   Scalar( 0, 0, 255 ), FILLED );
+    }
+
+    imshow( "Histogram", histImg );
+    //! [Draw the histogram]
+}