java,image,colors,mapping,grayscale , Convert grayscale to color gradient in Java?

Convert grayscale to color gradient in Java?


Tag: java,image,colors,mapping,grayscale

Is there any general algorithm or a provided class for mapping a grayscale value (0-255) to a value in a colour gradient? I am thinking of something of the sorts:

   public Color mapGrayscaleValue (byte value, Color[] gradientColors);

I am wanting this to provide clearer highlights in what would otherwise be a grayscale cloud coverage radar image I have been provided.


If you are using java.awt.image, you should look in to IndexColorModel. It does (I think) exactly what you're looking for.

You will need to generate the 256 RGB values for the gradient somehow and create a model around them, then you can create a BufferedImage from the grayscale raster using the new model.

Here's a hopefully straightforward example of this:

index color model ex

import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;

class ColorModelEx implements Runnable {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new ColorModelEx());

    public void run() {
        JFrame frame = new JFrame();
        JLabel label;
        try {
            label = new JLabel(new ImageIcon(createImage(
        } catch (Exception e) {
            throw new AssertionError(e);


    static BufferedImage createImage(Color... colors) throws Exception {
        if ((256 % (colors.length - 1)) != 0)
            throw new IllegalArgumentException();

        BufferedImage original =

        final int w = original.getWidth();
        final int h = original.getHeight();

        BufferedImage gray =
            new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
        Graphics2D g2 = gray.createGraphics();
        g2.drawImage(original, 0, 0, null);

        byte[] r = new byte[256];
        byte[] g = new byte[256];
        byte[] b = new byte[256];

        final int fade = (256 / (colors.length - 1));

        // (generate all 256 RGB values by
        // fading between the colors supplied)
        for (int i = 0; i < 256; ++i) {
            Color c0 = colors[(i / fade)];
            Color c1 = colors[(i / fade) + 1];

            float amt = (i % fade) / ((float) fade);

            r[i] = getChannel(amt, c0.getRed(),   c1.getRed());
            g[i] = getChannel(amt, c0.getGreen(), c1.getGreen());
            b[i] = getChannel(amt, c0.getBlue(),  c1.getBlue());

        // (remap same pixels to new model)
        return new BufferedImage(
            new IndexColorModel(8, 256, r, g, b),
            gray.getRaster(), false, null);

    static byte getChannel(float amt, int ch0, int ch1) {
        return (byte)
            ((ch0 * (1 - amt)) + (ch1 * amt));

(Image from here.)

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