Creating ImageIcon from Image is very slow

Question

Hi I have a program which reads a number of files which may contain (amongst other things) image data in various formats such as JPG.I read scale this down into an image object fine, and then I want to display a small version of it on screen so I put the scale dimage into an ImageIcon which i display later using a JLabel.
Anyway it runs very slow , the funny thing is using JProbe Ive tracked the problem down to creation of the ImageIcon constructor, the actual thumbnail image creation is very quick.
Why does ImageIcon take so long or is there a simple way of displaying the image in a Swing Application
without using JLabel.
BufferedImage bi = ImageIO.read(new DataInputStream(new ByteArrayInputStream(imageData)));
Image thumbnaiImage = image.getScaledInstance(20,20Image.SCALE_FAST);
ImageIcon thumbnail     = new ImageIcon(thumbnailImage);

Answer 1

If you're not too picky about the image quality (and I see you're using SCALE_FAST), you can set the
source subsampling on your ImageReadParam so that you never construct the large image: you start
with the thumbnail.
import java.awt.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import java.util.*;
import javax.imageio.*;
import javax.swing.*;
public class AllThumbs {
    public static void main(String[] args) throws MalformedURLException {
        String prefix = "http://www3.us.porsche.com/english/usa/carreragt/modelinformation/experience/desktop/bilder/icon";
        String suffix = "_800x600.jpg";
        JPanel p = new JPanel(new GridLayout(0,3));
        for(int i=1; i<9; ++i) {
            try {
                p.add(getThumb(new URL(prefix + i + suffix), 200, 150));
            } catch (IOException e) {
                System.out.println(e.getMessage());
        JFrame f = new JFrame("AllThumbs");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(p);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    public static JLabel getThumb(URL url, int maxWidth, int maxHeight) throws IOException {
        String suffix = getSuffix(url);
        Iterator readers = ImageIO.getImageReadersBySuffix(suffix);
        if (!readers.hasNext())
            throw new IOException("No reader for suffix " + suffix);
        ImageReader reader = (ImageReader) readers.next();
        reader.setInput(ImageIO.createImageInputStream(url.openStream()), true, true);
        int w = reader.getWidth(0), h = reader.getHeight(0);
        int subsampling = Math.max(1, Math.max(w/maxWidth, h/maxHeight));
        ImageReadParam param = reader.getDefaultReadParam();
        param.setSourceSubsampling(subsampling, subsampling, 0, 0);
        BufferedImage image = reader.read(0, param);
        String path = url.getPath();
        String text = path.substring(1+path.lastIndexOf('/'));
        JLabel label = new JLabel(text, new ImageIcon(image), SwingConstants.CENTER);
        label.setHorizontalTextPosition(SwingConstants.CENTER);
        label.setVerticalTextPosition(SwingConstants.BOTTOM);
        label.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
        return label;
    public static String getSuffix(URL url) throws IOException {
        String path = url.getPath();
        int dot = path.lastIndexOf('.');
        if (dot == -1)
            throw new IOException("No . in " + path);
        return path.substring(1+dot);
}It is also possible for there to be thumbnail images stored in an image file. (These thumbnails
don't even have to be related to the main image.) ImageIO has methods to read these directly,
so if you have control over your image files you can create them with thumbnails in place.