Applying filters to PNG Images

Question

Hi
I would like to know how to implement filters or Operators such as Alpha filtering,LookupOp,ConvolveOp (or any kind of filter which makes the image blur or partially transparent) to a PNG Image and then revert back to the original image.
Thanks,Laksh

Answer 1

1. Have you tried doing the tutorial?
2. What do you mean by "revert back to the original image" -- are you trying to find filters that are the inverse of other filters?
Here's a demo. I create a buffered image, write it out to a png file and read it back in.
Then I convert its type (the blur filter didn't want to work, otherwise!!). I run the
image through the filter and save it to another file, displaying the images along the way.
import java.awt.*;
import java.awt.font.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;
public class Example {
    public static void main(String[] args) throws IOException {
        File file = new File("temp.png");
        ImageIO.write(createSampleImage(), "png", file);
        BufferedImage source = ImageIO.read(file);
        System.out.println("type = " + source.getType());
        BufferedImage converted = convertType(source, BufferedImage.TYPE_INT_RGB);
        BufferedImage blurred = blur(converted);
        ImageIO.write(blurred, "png", new File("blurred.png"));
        JPanel panel = new JPanel(new GridLayout(0,1));
        addImage(panel, source, "from png file");
        addImage(panel, converted, "TYPE_INT_RGB source");
        addImage(panel, blurred, "blurred image");
        JFrame f = new JFrame("Example");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(new JScrollPane(panel));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    static void addImage(Container cp, BufferedImage image, String title) {
        JLabel label = new JLabel(new ImageIcon(image));
        label.setBorder(BorderFactory.createTitledBorder(title));
        cp.add(label);
    static BufferedImage createSampleImage() {
        Font font = new Font("Lucida Bright", Font.ITALIC, 72);
        String text = "Sample Text";
        Rectangle2D bounds = font.getStringBounds(text, new FontRenderContext(null, true, true));
        int w = (int) Math.ceil(bounds.getWidth());
        int h = (int) Math.ceil(bounds.getHeight());
        BufferedImage image = new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);
        Graphics2D g = image.createGraphics();
        g.setFont(font);
        g.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
        g.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
        g.setPaint(Color.WHITE);
        g.fillRect(0, 0, w, h);
        g.setPaint(Color.BLACK);
        g.drawString(text, (float) -bounds.getX(), (float) -bounds.getY());
        g.dispose();
        return image;
    public static BufferedImage convertType(BufferedImage source, int type) {
        if (source.getType() == type)
            return source;
        BufferedImage result = new BufferedImage(source.getWidth(), source.getHeight(), type);
        Graphics2D g = result.createGraphics();
        g.drawRenderedImage(source, null);
        g.dispose();
        return result;
    static BufferedImage blur(BufferedImage image) {
        BufferedImage result = new BufferedImage(
                image.getWidth(), image.getHeight(), BufferedImage.TYPE_INT_RGB);
        float ninth = 1.0f / 9.0f;
        float[] kernel = {ninth, ninth, ninth, ninth, ninth, ninth, ninth, ninth, ninth};
        ConvolveOp op = new ConvolveOp(new Kernel(3, 3, kernel), ConvolveOp.EDGE_NO_OP, null);
        return op.filter(image,result);