content: import java.util.ArrayList;
  import java.util.List;
  
  import org.opencv.core.Core;
  import org.opencv.core.CvType;
  import org.opencv.core.Mat;
  import org.opencv.core.MatOfFloat;
  import org.opencv.core.MatOfInt;
  import org.opencv.core.Point;
  import org.opencv.core.Scalar;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  import org.opencv.imgproc.Imgproc;
  
  class CalcHist {
      public void run(String[] args) {
          //! [Load image]
          String filename = args.length > 0 ? args[0] : "../data/lena.jpg";
          Mat src = Imgcodecs.imread(filename);
          if (src.empty()) {
              System.err.println("Cannot read image: " + filename);
              System.exit(0);
          }
          //! [Load image]
  
          //! [Separate the image in 3 places ( B, G and R )]
          List<Mat> bgrPlanes = new ArrayList<>();
          Core.split(src, bgrPlanes);
          //! [Separate the image in 3 places ( B, G and R )]
  
          //! [Establish the number of bins]
          int histSize = 256;
          //! [Establish the number of bins]
  
          //! [Set the ranges ( for B,G,R) )]
          float[] range = {0, 256}; //the upper boundary is exclusive
          MatOfFloat histRange = new MatOfFloat(range);
          //! [Set the ranges ( for B,G,R) )]
  
          //! [Set histogram param]
          boolean accumulate = false;
          //! [Set histogram param]
  
          //! [Compute the histograms]
          Mat bHist = new Mat(), gHist = new Mat(), rHist = new Mat();
          Imgproc.calcHist(bgrPlanes, new MatOfInt(0), new Mat(), bHist, new MatOfInt(histSize), histRange, accumulate);
          Imgproc.calcHist(bgrPlanes, new MatOfInt(1), new Mat(), gHist, new MatOfInt(histSize), histRange, accumulate);
          Imgproc.calcHist(bgrPlanes, new MatOfInt(2), new Mat(), rHist, new MatOfInt(histSize), histRange, accumulate);
          //! [Compute the histograms]
  
          //! [Draw the histograms for B, G and R]
          int histW = 512, histH = 400;
          int binW = (int) Math.round((double) histW / histSize);
  
          Mat histImage = new Mat( histH, histW, CvType.CV_8UC3, new Scalar( 0,0,0) );
          //! [Draw the histograms for B, G and R]
  
          //! [Normalize the result to ( 0, histImage.rows )]
          Core.normalize(bHist, bHist, 0, histImage.rows(), Core.NORM_MINMAX);
          Core.normalize(gHist, gHist, 0, histImage.rows(), Core.NORM_MINMAX);
          Core.normalize(rHist, rHist, 0, histImage.rows(), Core.NORM_MINMAX);
          //! [Normalize the result to ( 0, histImage.rows )]
  
          //! [Draw for each channel]
          float[] bHistData = new float[(int) (bHist.total() * bHist.channels())];
          bHist.get(0, 0, bHistData);
          float[] gHistData = new float[(int) (gHist.total() * gHist.channels())];
          gHist.get(0, 0, gHistData);
          float[] rHistData = new float[(int) (rHist.total() * rHist.channels())];
          rHist.get(0, 0, rHistData);
  
          for( int i = 1; i < histSize; i++ ) {
              Imgproc.line(histImage, new Point(binW * (i - 1), histH - Math.round(bHistData[i - 1])),
                      new Point(binW * (i), histH - Math.round(bHistData[i])), new Scalar(255, 0, 0), 2);
              Imgproc.line(histImage, new Point(binW * (i - 1), histH - Math.round(gHistData[i - 1])),
                      new Point(binW * (i), histH - Math.round(gHistData[i])), new Scalar(0, 255, 0), 2);
              Imgproc.line(histImage, new Point(binW * (i - 1), histH - Math.round(rHistData[i - 1])),
                      new Point(binW * (i), histH - Math.round(rHistData[i])), new Scalar(0, 0, 255), 2);
          }
          //! [Draw for each channel]
  
          //! [Display]
          HighGui.imshow( "Source image", src );
          HighGui.imshow( "calcHist Demo", histImage );
          HighGui.waitKey(0);
          //! [Display]
  
          System.exit(0);
      }
  }
  
  public class CalcHistDemo {
      public static void main(String[] args) {
          // Load the native OpenCV library
          System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
  
          new CalcHist().run(args);
      }
  }
  