Added tutorial for BackProject in cpp (demo 2) - tutorial code

samples/cpp/tutorial_code/Histograms_Matching/calcBackProject_Demo2.cpp

+/**
+ * @file BackProject_Demo2.cpp
+ * @brief Sample code for backproject function usage ( a bit more elaborated )
+ * @author OpenCV team
+ */
+
+#include "opencv2/imgproc/imgproc.hpp"
+#include "opencv2/highgui/highgui.hpp"
+
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+/// Global Variables
+Mat src; Mat hsv; Mat hue; 
+Mat mask;
+
+int lo = 20; int up = 20;
+char* window_image = "Source image";
+
+/// Function Headers
+void Hist_and_Backproj( );
+void pickPoint (int event, int x, int y, int, void* );
+
+/**
+ * @function main
+ */
+int main( int argc, char** argv )
+{
+  /// Read the image
+  src = imread( argv[1], 1 );
+  /// Transform it to HSV
+  cvtColor( src, hsv, CV_BGR2HSV );
+
+  /// Use only the Hue value
+  hue.create( hsv.size(), hsv.depth() );
+
+  int ch[] = { 0, 0 };
+  mixChannels( &hsv, 1, &hue, 1, ch, 1 );  
+
+  /// Show the image 
+  namedWindow( window_image, CV_WINDOW_AUTOSIZE );
+  imshow( window_image, src );
+
+  /// Set Trackbars for floodfill thresholds
+  createTrackbar( "Low thresh", window_image, &lo, 255, 0 );
+  createTrackbar( "High thresh", window_image, &up, 255, 0 );
+  /// Set a Mouse Callback
+  setMouseCallback( window_image, pickPoint, 0 );
+
+  waitKey(0);
+  return 0;
+}
+
+/**
+ * @function pickPoint
+ */
+void pickPoint (int event, int x, int y, int, void* )
+{
+  if( event != CV_EVENT_LBUTTONDOWN )
+    { return; }
+
+  // Fill and get the mask
+  Point seed = Point( x, y );
+ 
+  int newMaskVal = 255;
+  Scalar newVal = Scalar( 120, 120, 120 );
+
+  int connectivity = 8;
+  int flags = connectivity + (newMaskVal << 8 ) + FLOODFILL_FIXED_RANGE + FLOODFILL_MASK_ONLY;
+
+  Mat mask2 = Mat::zeros( src.rows + 2, src.cols + 2, CV_8UC1 );
+  floodFill( src, mask2, seed, newVal, 0, Scalar( lo, lo, lo ), Scalar( up, up, up), flags ); 
+  mask = mask2( Range( 1, mask2.rows - 1 ), Range( 1, mask2.cols - 1 ) );
+  cout<<"rows: "<<mask.rows<<" columns: "<<mask.cols<<endl;
+  imshow( "Mask", mask );
+
+  Hist_and_Backproj( );
+}
+
+/**
+ * @function Hist_and_Backproj
+ */
+void Hist_and_Backproj( )
+{
+  MatND hist;
+  int h_bins = 30; int s_bins = 32;
+  int histSize[] = { h_bins, s_bins }; 
+
+  float h_range[] = { 0, 179 };
+  float s_range[] = { 0, 255 };
+  const float* ranges[] = { h_range, s_range };
+
+  int channels[] = { 0, 1 };
+
+  /// Get the Histogram and normalize it
+  calcHist( &hsv, 1, channels, mask, hist, 2, histSize, ranges, true, false );
+
+  normalize( hist, hist, 0, 255, NORM_MINMAX, -1, Mat() );
+
+  /// Get Backprojection
+  MatND backproj;
+  calcBackProject( &hsv, 1, channels, hist, backproj, ranges, 1, true );
+ 
+  /// Draw the backproj
+  imshow( "BackProj", backproj );
+
+}