BuffededImage cache

[tim]

Hello everyone

I've been using BufferedImage objects for some time and I noticed something strange. When I use the ImageIO.read() method to read an image from the hard drive and I draw the image somewhere in a thread, I found that it is very slow. But, if I load the image in some BufferedImage object, say A, create a new Instance of BufferedImage B and draw A onto B using the BufferedImage.getGraphics() method, I found that rendering B is much faster. Can someone please explain this and perhaps show me a better way of using the BufferedImage for performance.

Thank you :D

[hardwired]

Try an image type based on your local configuration.
On ms vista I get:

C:\jexp>java ImageTypes
loaded image type   = 5
compatible dst type = 1

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.*;

public class ImageTypes {
    private JScrollPane getContent(BufferedImage image) {
        System.out.println("loaded image type   = " + image.getType());
        JPanel panel = new JPanel(new GridLayout(1,0));
        panel.add(wrap(image));
        panel.add(wrap(convert(image)));
        panel.add(wrap(convert(image, BufferedImage.TYPE_INT_RGB)));
        return new JScrollPane(panel);
    }

    private BufferedImage convert(BufferedImage src) {
        int w = src.getWidth();
        int h = src.getHeight();
        BufferedImage dst =
            GraphicsEnvironment.getLocalGraphicsEnvironment()
                               .getDefaultScreenDevice()
                               .getDefaultConfiguration()
                               .createCompatibleImage(w, h);
        // Component has a [i]getGraphicsConfiguration[/i] method.
        System.out.println("compatible dst type = " + dst.getType());
        Graphics2D g2 = dst.createGraphics();
        g2.drawImage(src,0,0,null);
        g2.dispose();
        return dst;
    }

    private BufferedImage convert(BufferedImage src, int type) {
        int w = src.getWidth();
        int h = src.getHeight();
        BufferedImage dst = new BufferedImage(w, h, type);
        Graphics2D g2 = dst.createGraphics();
        g2.drawImage(src,0,0,null);
        g2.dispose();
        return dst;
    }

    private JLabel wrap(BufferedImage image) {
        JLabel label = new JLabel(new ImageIcon(image));
        label.setHorizontalAlignment(JLabel.CENTER);
        return label;
    }

    public static void main(String[] args) throws IOException {
        String path = "images/blackBear.jpg";
        BufferedImage image = ImageIO.read(new File(path));
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new ImageTypes().getContent(image));
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}