import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.util.*;
import javax.swing.filechooser.*;
import java.io.*;

public class ChooseFile extends JPanel implements ActionListener {
    JButton go;
    String sourceFolder="";
    String theFile="";
    JFileChooser chooser;
    String choosertitle;
    public ChooseFile() {
       go = new JButton("Choose Folder");
       go.addActionListener(this);
       add(go);
    }

    public void actionPerformed(ActionEvent e) {

        System.out.println("Button Clicked");
        chooser = new JFileChooser();
        chooser.setCurrentDirectory(new java.io.File("."));
        chooser.setDialogTitle(choosertitle);
        FileNameExtensionFilter filter = new FileNameExtensionFilter("JPG, PNG & GIF Images", "jpg", "gif", "png");
        chooser.setFileFilter(filter);
        chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);

        if (chooser.showOpenDialog(this) == JFileChooser.APPROVE_OPTION) {
            String dirr = "" + chooser.getCurrentDirectory();
            File file = chooser.getSelectedFile();
            if(dirr.substring(dirr.length()-1,dirr.length()).equals(".")){
                dirr = dirr.substring(0,dirr.length()-1);
                sourceFolder=""+dirr + "" + file.getName();
            } else{
               sourceFolder=""+dirr + "/" + file.getName();
            }
            System.out.println("Folder path: " + dirr + " | File Name: " + file.getName());
            System.out.println(sourceFolder);
            ExamineImage.lum(sourceFolder);
        } else {
            System.out.println("No Selection ");
        }
    }

    public Dimension getPreferredSize(){
        return new Dimension(200, 200);
    }

    public static void main(String s[]) {
        JFrame frame = new JFrame("");
        ChooseFile panel = new ChooseFile();
        frame.addWindowListener(
        new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        }
        );
        frame.getContentPane().add(panel,"Center");
        frame.setSize(panel.getPreferredSize());
        frame.setVisible(true);
    }
}
========================================================
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.AffineTransform;
import java.awt.image.*;
import javax.imageio.*;
import javax.swing.*;
import java.awt.AlphaComposite;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.swing.ImageIcon;
import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class ExamineImage{
    public static void lum(String ffile) {
        BufferedImage img=null;

        File myFile = new File(ffile);
        //File[] listOfFiles = myFolder.listFiles();

        try{
            if (myFile.isFile()) {
                img = ImageIO.read(myFile);
                int width = 0;
                int height = 0;
                int count = 0;
                double avg = 0;
                double sum = 0;
                if(img!=null){
                    width  = img.getWidth();
                    height  = img.getHeight();
                }
                System.out.println("Width " + width + " " +  height);
                for(int x = 0; x < width; x++){
                    for (int y = 0;y < height; y++){
                        int pixelCol = img.getRGB(x, y);
                        int a = (pixelCol >>> 24) & 0xff;
                        int r = (pixelCol >>> 16) & 0xff;
                        int g = (pixelCol >>> 8) & 0xff;
                        int b = pixelCol & 0xff;
                        double lum = (0.2126*r) + (0.7152*g) + (0.0722*b);
                        sum += lum;
                        count++;
                    }
                }
                avg = sum/count;
                System.out.println("The average luminance is " + avg);
            }
        }catch(Exception e){
            System.out.println("THERE WAS A PROBLEM " + e);
        }
    }//end of lumanance method
}