Light weight components do not get default focus. Under JDK1.1.4 this worked on the WIN32 platform but not on the Solaris platform. In later releases it did not work at all. The ImageCanvas light weight component never gets focus and therefore never gets KeyEvents.

There is a program called canFilterIndexColorModel.java that can be found on page 1312-1313 of The Java(tm) Class Libraries Second Edition, Volume 2 that demonstrates this problem.

import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import java.util.*;

class Main extends Frame {
   Main(String filename) {
       super("canFileIndexColorModel Example");
add(new ImageCanvas(getToolkit().getImage(filename)),
           BorderLayout.CENTER);

       setSize(50, 100);
       show();

   }

   static public void main(String[] args) {
       if (args.length == 1) {
           new Main(args[0]);
       } else {
           System.err.println("usage: java Main <image files>");
       }
   }
}

class ImageCanvas extends Component {
    Image brightImage;
    Image image;
    BrightnessFilter imgf = new BrightnessFilter();

    ImageCanvas(Image image) {
        this.image = image;
        processImage();
        addKeyListener(new KeyEventHandler());
    }

    public void paint(Graphics g) {
        g.drawImage(brightImage, 0, 0, this);
    }

    void processImage() {
        ImageProducer ip = image.getSource();

        ip = new FilteredImageSource(ip, imgf);
        brightImage = getToolkit().createImage(ip);
        repaint();
    }
    class KeyEventHandler extends KeyAdapter {
        public void keyTyped(KeyEvent evt) {
            char key = evt.getKeyChar();
            if (key == '+') {
                imgf.addBrightness(.1f);
            } else if (key == '-') {
                imgf.addBrightness(-.1f);
            }
            processImage();
        }
    }
 
}

class BrightnessFilter extends RGBImageFilter {
    float bDelta;
    float[] hsb = new float[3];
    int width, height;

    BrightnessFilter() {
        canFilterIndexColorModel = true;
    }

    public void setDimensions(int w, int h) {
        super.setDimensions(w, h);
        width = w;
        height = h;
    }

    public void addBrightness(float f) {
        bDelta += f;
    }

    public int filterRGB(int x, int y, int rgb) {
        // x and y are both -1
        Color c = new Color(rgb);
        Color.RGBtoHSB(c.getRed(), c.getGreen(), c.getBlue(), hsb);
        hsb[2] = Math.max(0.0f, Math.min(1.0f, hsb[2] + bDelta));
        return Color.HSBtoRGB(hsb[0], hsb[1], hsb[2]);
    }
}