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samples/cpp/tutorial_code/Histograms_Matching/compareHist_Demo.cpp

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+/**
+ * @file compareHist_Demo.cpp
+ * @brief Sample code to use the function compareHist
+ * @author OpenCV team
+ */
+
+#include "opencv2/imgcodecs.hpp"
+#include "opencv2/highgui.hpp"
+#include "opencv2/imgproc.hpp"
+#include <iostream>
+
+using namespace std;
+using namespace cv;
+
+const char* keys =
+    "{ help  h| | Print help message. }"
+    "{ @input1 | | Path to input image 1. }"
+    "{ @input2 | | Path to input image 2. }"
+    "{ @input3 | | Path to input image 3. }";
+
+/**
+ * @function main
+ */
+int main( int argc, char** argv )
+{
+    //! [Load three images with different environment settings]
+    CommandLineParser parser( argc, argv, keys );
+    Mat src_base = imread( parser.get<String>("input1") );
+    Mat src_test1 = imread( parser.get<String>("input2") );
+    Mat src_test2 = imread( parser.get<String>("input3") );
+    if( src_base.empty() || src_test1.empty() || src_test2.empty() )
+    {
+        cout << "Could not open or find the images!\n" << endl;
+        parser.printMessage();
+        return -1;
+    }
+    //! [Load three images with different environment settings]
+
+    //! [Convert to HSV]
+    Mat hsv_base, hsv_test1, hsv_test2;
+    cvtColor( src_base, hsv_base, COLOR_BGR2HSV );
+    cvtColor( src_test1, hsv_test1, COLOR_BGR2HSV );
+    cvtColor( src_test2, hsv_test2, COLOR_BGR2HSV );
+    //! [Convert to HSV]
+
+    //! [Convert to HSV half]
+    Mat hsv_half_down = hsv_base( Range( hsv_base.rows/2, hsv_base.rows ), Range( 0, hsv_base.cols ) );
+    //! [Convert to HSV half]
+
+    //! [Using 50 bins for hue and 60 for saturation]
+    int h_bins = 50, s_bins = 60;
+    int histSize[] = { h_bins, s_bins };
+
+    // hue varies from 0 to 179, saturation from 0 to 255
+    float h_ranges[] = { 0, 180 };
+    float s_ranges[] = { 0, 256 };
+
+    const float* ranges[] = { h_ranges, s_ranges };
+
+    // Use the 0-th and 1-st channels
+    int channels[] = { 0, 1 };
+    //! [Using 50 bins for hue and 60 for saturation]
+
+    //! [Calculate the histograms for the HSV images]
+    Mat hist_base, hist_half_down, hist_test1, hist_test2;
+
+    calcHist( &hsv_base, 1, channels, Mat(), hist_base, 2, histSize, ranges, true, false );
+    normalize( hist_base, hist_base, 0, 1, NORM_MINMAX, -1, Mat() );
+
+    calcHist( &hsv_half_down, 1, channels, Mat(), hist_half_down, 2, histSize, ranges, true, false );
+    normalize( hist_half_down, hist_half_down, 0, 1, NORM_MINMAX, -1, Mat() );
+
+    calcHist( &hsv_test1, 1, channels, Mat(), hist_test1, 2, histSize, ranges, true, false );
+    normalize( hist_test1, hist_test1, 0, 1, NORM_MINMAX, -1, Mat() );
+
+    calcHist( &hsv_test2, 1, channels, Mat(), hist_test2, 2, histSize, ranges, true, false );
+    normalize( hist_test2, hist_test2, 0, 1, NORM_MINMAX, -1, Mat() );
+    //! [Calculate the histograms for the HSV images]
+
+    //! [Apply the histogram comparison methods]
+    for( int compare_method = 0; compare_method < 4; compare_method++ )
+    {
+        double base_base = compareHist( hist_base, hist_base, compare_method );
+        double base_half = compareHist( hist_base, hist_half_down, compare_method );
+        double base_test1 = compareHist( hist_base, hist_test1, compare_method );
+        double base_test2 = compareHist( hist_base, hist_test2, compare_method );
+
+        cout << "Method " << compare_method << " Perfect, Base-Half, Base-Test(1), Base-Test(2) : "
+             <<  base_base << " / " << base_half << " / " << base_test1 << " / " << base_test2 << endl;
+    }
+    //! [Apply the histogram comparison methods]
+
+    cout << "Done \n";
+    return 0;
+}