OpenCV Contrast Use Equalize Hist For RBG

<h5>Goal</h5>
Test OpenCV Equalize Hist with split RGB channel then merge to original image.

```OpenCV_ContrastUseEqualizeHistForRBG.java
import java.awt.EventQueue;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

public class OpenCV_ContrastUseEqualizeHistForRBG {

    static {System.loadLibrary(Core.NATIVE_LIBRARY_NAME);}
    private JFrame frmjavaSwing;
    double alpha =2;
    double beta = 2;

    /**
     *  Launch the application.
     */
    public static void main(String[] args){
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try{
                    OpenCV_ContrastUseEqualizeHistForRBG window = new OpenCV_ContrastUseEqualizeHistForRBG();
                    window.frmjavaSwing.setVisible(true);
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     *  Create the application.
     */
    public OpenCV_ContrastUseEqualizeHistForRBG(){
        init();
    }

    /**
     *  Init the contents of the frame.
     */
    private void init(){
        final Mat source = Imgcodecs.imread("D:\\projects\\Java\\OpenCV_Samples\\resource\\imgs\\clean.jpg");

        BufferedImage image=matToBufferedImage(equalizeHist(source));

        frmjavaSwing = new JFrame();
        frmjavaSwing.setTitle("opencv彩色影像對比練習1");
        frmjavaSwing.setBounds(100, 100, 520, 550);
        frmjavaSwing.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frmjavaSwing.getContentPane().setLayout(null);

        final JLabel lblNewLabel = new JLabel("");
        lblNewLabel.setBounds(10, 10, 438, 455);
        lblNewLabel.setIcon(new ImageIcon(image));
        frmjavaSwing.getContentPane().add(lblNewLabel);
    }

    public Mat equalizeHist(Mat source){
        Mat destination=new Mat(source.rows(),source.cols(),source.type());
        List<Mat> bgrList = new ArrayList<>(3);
        Core.split(source,  bgrList);
        Imgproc.equalizeHist(bgrList.get(0), bgrList.get(0));
        Imgproc.equalizeHist(bgrList.get(1), bgrList.get(1));
        Imgproc.equalizeHist(bgrList.get(2), bgrList.get(2));
        Core.merge(bgrList, destination);
        return destination;
    }

    public BufferedImage matToBufferedImage(Mat matrix) {
        int cols = matrix.cols();
        int rows = matrix.rows();
        int elemSize = (int)matrix.elemSize();
        byte[] data = new byte[cols * rows * elemSize];
        int type;
        matrix.get(0, 0, data);
        switch (matrix.channels()) {
            case 1:
                type = BufferedImage.TYPE_BYTE_GRAY;
                break;
            case 3:
                type = BufferedImage.TYPE_3BYTE_BGR;
                // bgr to rgb
                byte b;
                for(int i=0; i<data.length; i=i+3) {
                    b = data[i];
                    data[i] = data[i+2];
                    data[i+2] = b;
                }
                break;
            default:
                return null;
        }
        BufferedImage image2 = new BufferedImage(cols, rows, type);
        image2.getRaster().setDataElements(0, 0, cols, rows, data);
        return image2;
    }
}
```
![opencv_contrast_use_equalize_hist_for_rgb.JPG](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/276243/f7578eef-d0e1-515c-c8a0-aae42d467672.jpeg)