How to change the brightness of an Image

Question

My Question: I want to be able to change the brightness of a resource image and have three instances of it as ImageIcons. One at 50% brightness (so darker), ano

Answer 1

I would suggest just writing over the image with a semi-transparent black.

Assuming you want to write directly on the image:

Graphics g = img.getGraphics();
float percentage = .5f; // 50% bright - change this (or set dynamically) as you feel fit
int brightness = (int)(256 - 256 * percentage);
g.setColor(new Color(0,0,0,brightness));
g.fillRect(0, 0, img.getWidth(), img.getHeight());

Or if you're just using the image for display purposes, do it in the paintComponent method. Here's an SSCCE:

import java.awt.*;
import java.awt.image.*;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;


public class ImageBrightener extends JPanel{

    BufferedImage img;
    float percentage = 0.5f;

    public Dimension getPreferredSize(){
        return new Dimension(img.getWidth(), img.getHeight());
    }

    public ImageBrightener(){
        try {
            img = ImageIO.read(new URL("http://media.giantbomb.com/uploads/0/1176/230441-thehoff_super.jpeg"));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(img, 0, 0, this);
        int brightness = (int)(256 - 256 * percentage);
        g.setColor(new Color(0,0,0,brightness));
        g.fillRect(0, 0, getWidth(), getHeight());
    }

    public static void main(String[] args){
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new ImageBrightener());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

EDIT

Assuming the same code as above, you can manipulate everything besides the Alpha by messing with the rasterizer. Here's an example (paint shadedImage instead of img if using this exmaple). Please note this doesn't catch edge cases of RGB values greater than 256 and less than 0.

        img = ImageIO.read(new URL("http://media.giantbomb.com/uploads/0/1176/230441-thehoff_super.jpeg"));
        shadedImage = new BufferedImage(img.getWidth(), img.getWidth(), BufferedImage.TYPE_INT_ARGB);
        shadedImage.getGraphics().drawImage(img, 0, 0, this);

        WritableRaster wr = shadedImage.getRaster();
        int[] pixel = new int[4];

        for(int i = 0; i < wr.getWidth(); i++){
            for(int j = 0; j < wr.getHeight(); j++){
                wr.getPixel(i, j, pixel);
                pixel[0] = (int) (pixel[0] * percentage);
                pixel[1] = (int) (pixel[1] * percentage);
                pixel[2] = (int) (pixel[2] * percentage);
                wr.setPixel(i, j, pixel);
            }
        }