Added calcHist_Demo.cpp tutorial code

samples/cpp/tutorial_code/Histograms_Matching/calcHist_Demo.cpp

+/**
+ * @function calcHist_Demo.cpp
+ * @brief Demo code to use the function calcHist
+ * @author
+ */
+
+#include "opencv2/highgui/highgui.hpp"
+#include "opencv2/imgproc/imgproc.hpp"
+#include <iostream>
+#include <stdio.h>
+
+using namespace std;
+using namespace cv;
+
+/**
+ * @function main
+ */
+int main( int argc, char** argv )
+{
+  Mat src, dst;
+
+  /// Load image
+  src = imread( argv[1], 1 );
+
+  if( !src.data )
+    { return -1; }
+
+  /// Separate the image in 3 places ( R, G and B )
+  vector<Mat> rgb_planes;
+  split( src, rgb_planes ); 
+
+  /// Establish the number of bins 
+  int histSize = 255;
+
+  /// Set the ranges ( for R,G,B) )
+  float range[] = { 0, 255 } ; 
+  const float* histRange = { range };
+
+  bool uniform = true; bool accumulate = false;
+
+  Mat r_hist, g_hist, b_hist;
+
+  /// Compute the histograms:
+  calcHist( &rgb_planes[0], 1, 0, Mat(), r_hist, 1, &histSize, &histRange, uniform, accumulate );
+  calcHist( &rgb_planes[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRange, uniform, accumulate );
+  calcHist( &rgb_planes[2], 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate );
+
+  // Draw the histograms for R, G and B
+  int hist_w = 400; int hist_h = 400;
+  int bin_w = cvRound( (double) hist_w/histSize );
+
+  Mat histImage( hist_w, hist_h, CV_8UC3, Scalar( 0,0,0) );
+
+  /// Normalize the result to [ 0, histImage.rows ]
+  normalize(r_hist, r_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
+  normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
+  normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
+
+  /// Draw for each channel 
+  for( int i = 1; i < histSize; i++ )
+    { 
+      line( histImage, Point( bin_w*(i-1), hist_h - cvRound(r_hist.at<float>(i-1)) ) , 
+		       Point( bin_w*(i), hist_h - cvRound(r_hist.at<float>(i)) ), 
+	               Scalar( 0, 0, 255), 2, 8, 0  ); 
+      line( histImage, Point( bin_w*(i-1), hist_h - cvRound(g_hist.at<float>(i-1)) ) , 
+		       Point( bin_w*(i), hist_h - cvRound(g_hist.at<float>(i)) ), 
+	               Scalar( 0, 255, 0), 2, 8, 0  ); 
+      line( histImage, Point( bin_w*(i-1), hist_h - cvRound(b_hist.at<float>(i-1)) ) , 
+		       Point( bin_w*(i), hist_h - cvRound(b_hist.at<float>(i)) ), 
+	               Scalar( 255, 0, 0), 2, 8, 0  );       
+    }
+
+ /// Display 
+  namedWindow("calcHist Demo", CV_WINDOW_AUTOSIZE );
+  imshow("calcHist Demo", histImage );
+
+  waitKey(0);
+
+  return 0;
+ 
+}