Brightness/Contrast of an indexed image

Question

Hi all,
Is it possible to change the Brightness/Contrast of an indexed image?
I've tried that with the following code:
// Brighten the image by 30%
float scaleFactor = 1.3f;
RescaleOp op = new RescaleOp(scaleFactor, 0, null);
bufferedIm = op.filter(bufferedIm, null);but it outputs:
java.lang.IllegalArgumentException: Rescaling cannot be performed on an indexed imageThanks in advance

Answer 1

Just roll your own: get the color components of the IndexColorModel, rescale them, build a new
IndexColorModel from that and put that together with the original WriteableRaster to form the
rescaled BufferedImage:
import java.awt.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import javax.imageio.*;
import javax.swing.*;
public class RescalingICMExample {
    public static void main(String[] args) throws IOException {
        URL url = new URL("http://weblogs.java.net/jag/bio/JagHeadshot-small.jpg");
        BufferedImage original = ImageIO.read(url);
        BufferedImage index = convertType(original, BufferedImage.TYPE_BYTE_INDEXED);
        JPanel p = new JPanel(new GridLayout(2,4));
        addToPanel(p, original, "original image");
        addToPanel(p, index, "indexed version");
        float[] scales = {1f, 1.1f, 1.2f, 1.3f, 1.3f, 1.3f};
        float[] offsets = {48, 32, 16, 0, 16, 32};
        for(int i=0; i<scales.length; ++i) {
            float s = scales;
float o = offsets[i];
addToPanel(p, rescale(index, s, o), "scale=" + s + ", offset="+o);
JFrame f = new JFrame("");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(p);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
public static BufferedImage convertType(BufferedImage image, int type) {
if (image.getType() == type)
return image;
BufferedImage result = new BufferedImage(image.getWidth(), image.getHeight(), type);
Graphics2D g = result.createGraphics();
g.drawRenderedImage(image, null);
g.dispose();
return result;
static void addToPanel(JPanel p, BufferedImage image, String title) {
JLabel label = new JLabel(new ImageIcon(image));
label.setBorder(BorderFactory.createTitledBorder(title));
p.add(label);
public static IndexColorModel rescale(IndexColorModel icm, float scaleFactor, float offset) {
int size = icm.getMapSize();
byte[] reds=new byte[size], greens=new byte[size], blues=new byte[size], alphas=new byte[size];
icm.getReds(reds);
icm.getGreens(greens);
icm.getBlues(blues);
icm.getAlphas(alphas);
rescale(reds, scaleFactor, offset);
rescale(greens, scaleFactor, offset);
rescale(blues, scaleFactor, offset);
return new IndexColorModel(8, size, reds, greens, blues, alphas);
public static void rescale(byte[] comps, float scaleFactor, float offset) {
for(int i=0; i<comps.length; ++i) {
int comp = 0xff & comps[i];
int newComp = Math.round(comp*scaleFactor+offset);
if (newComp < 0)
newComp = 0;
else if (newComp > 255)
newComp = 255;
comps[i] = (byte) newComp;
public static BufferedImage rescale(BufferedImage indexed, float scaleFactor, float offset) {
IndexColorModel icm = (IndexColorModel) indexed.getColorModel();
return new BufferedImage(rescale(icm, scaleFactor, offset), indexed.getRaster(), false, null);