How to convert Colors to Grayscale in java with just the java.io.*; library?

Question

Well, i got this.. cause in my place they request it like that.. Well i have this: //some variables and coments are a possible code.. But i mean i don\'t know how to do it exact

Answer 1

Most image formats have header information before the pixel data, so when you're reading these types of files, you need to take that into consideration...

Frankly, it's much easier to rely on pre-existing library where you can.

ImageIO allows you to read and write a number of different file formats, including BMP.

Take a look at

• Reading/Loading an Image
• Writing/Saving an Image

The next decision is - do you convert the image yourself or use a pre-existing filter. You'll have to do some of your own metrics, but in the past, I've found pixel manipulation of an image to be slow, slower than the in built filters at the very least...

Original, manual grayscale, automatical/filter grayscale

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.color.ColorSpace;
import java.awt.image.BufferedImage;
import java.awt.image.ColorConvertOp;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class GrayScaleImage {

    public static void main(String[] args) {
        new GrayScaleImage();
    }

    public GrayScaleImage() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridLayout(0, 3));
            try {
                BufferedImage master = ImageIO.read(new File("/path/to/file.bmp"));
                BufferedImage gray = ImageIO.read(new File("/path/to/file.bmp"));

                // Manual manipulation...
                for (int x = 0; x < gray.getWidth(); x++) {
                    for (int y = 0; y < gray.getHeight(); y++) {
                        Color color = new Color(gray.getRGB(x, y));
                        int red = color.getRed();
                        int green = color.getGreen();
                        int blue = color.getBlue();

                        red = green = blue = (int)(red * 0.299 + green * 0.587 + blue * 0.114);
                        color = new Color(red, green, blue);
                        int rgb = color.getRGB();
                        gray.setRGB(x, y, rgb);
                    }
                }

                BufferedImage grayScale = ImageIO.read(new File("/path/to/file.bmp"));

                // Automatic converstion....
                ColorConvertOp op = new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_GRAY), null);
                op.filter(grayScale, grayScale);

                add(new JLabel(new ImageIcon(master)));
                add(new JLabel(new ImageIcon(gray)));
                add(new JLabel(new ImageIcon(grayScale)));
            } catch (IOException ex) {
                Logger.getLogger(GrayScaleImage.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    }        
}

Now, writing the image (which is not demonstrated above) would be as simple as...

ImageIO.write(grayScale, "BMP", new File("/path/to/grayscale file.bmp"));