initial commit

samples/cpp/tutorial_code/snippets/imgproc_calcHist.cpp

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+#include <opencv2/imgproc.hpp>
+#include <opencv2/highgui.hpp>
+
+using namespace cv;
+
+int main( int argc, char** argv )
+{
+    Mat src, hsv;
+    if( argc != 2 || !(src=imread(argv[1], 1)).data )
+        return -1;
+
+    cvtColor(src, hsv, COLOR_BGR2HSV);
+
+    // Quantize the hue to 30 levels
+    // and the saturation to 32 levels
+    int hbins = 30, sbins = 32;
+    int histSize[] = {hbins, sbins};
+    // hue varies from 0 to 179, see cvtColor
+    float hranges[] = { 0, 180 };
+    // saturation varies from 0 (black-gray-white) to
+    // 255 (pure spectrum color)
+    float sranges[] = { 0, 256 };
+    const float* ranges[] = { hranges, sranges };
+    MatND hist;
+    // we compute the histogram from the 0-th and 1-st channels
+    int channels[] = {0, 1};
+
+    calcHist( &hsv, 1, channels, Mat(), // do not use mask
+             hist, 2, histSize, ranges,
+             true, // the histogram is uniform
+             false );
+    double maxVal=0;
+    minMaxLoc(hist, 0, &maxVal, 0, 0);
+
+    int scale = 10;
+    Mat histImg = Mat::zeros(sbins*scale, hbins*10, CV_8UC3);
+
+    for( int h = 0; h < hbins; h++ )
+        for( int s = 0; s < sbins; s++ )
+        {
+            float binVal = hist.at<float>(h, s);
+            int intensity = cvRound(binVal*255/maxVal);
+            rectangle( histImg, Point(h*scale, s*scale),
+                        Point( (h+1)*scale - 1, (s+1)*scale - 1),
+                        Scalar::all(intensity),
+                        -1 );
+        }
+
+    namedWindow( "Source", 1 );
+    imshow( "Source", src );
+
+    namedWindow( "H-S Histogram", 1 );
+    imshow( "H-S Histogram", histImg );
+    waitKey();
+}