如何通过BufferedImage将巨大的图像加载到Java？

Question

I want to load large images (18000 x 18000) to my application. If i use BufferedImage with type int_rgb , I need around 1235mb of heap memory to load. This is a very high amount of memory, and end users will likely have less ram (1GB or less).

On my development PC, when I load the image from MyEclipse IDE, it throws an out of memory Exception . When i pack my code to an executable jar and run it on my PC external of Eclipse, it still throws an exception.

How do I load such a large image into my application using buffered image without using 1235mb of memory? Is there a trick, like splitting the image into smaller portions like image segmentation?

I found this thread on SO , but it not useful for me; I want to load the image into BufferedImage and then draw it on a Panel using the Graphics class.

Answer 1

You can read and display fragments of the image using ImageReadParam from ImageIO package. Here is a basic example that illustrates how to read a single fragment using ImageReadParam without reading the whole image:

import java.awt.Image;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.imageio.ImageReadParam;
import javax.imageio.ImageReader;
import javax.imageio.stream.ImageInputStream;
import javax.swing.*;

public class TestImageChunks {
    private static void createAndShowUI() {
        try {
            URL url = new URL(
                    "http://duke.kenai.com/wave/.Midsize/Wave.png.png");
            Image chunk = readFragment(url.openStream(), new Rectangle(150,
                    150, 300, 250));
            JOptionPane.showMessageDialog(null, new ImageIcon(chunk), "Duke", 
                    JOptionPane.INFORMATION_MESSAGE);
        } catch (IOException e) {
            JOptionPane.showMessageDialog(null, e.getMessage(), "Failure",
                    JOptionPane.ERROR_MESSAGE);
            e.printStackTrace();
        }
    }

    public static BufferedImage readFragment(InputStream stream, Rectangle rect)
            throws IOException {
        ImageInputStream imageStream = ImageIO.createImageInputStream(stream);
        ImageReader reader = ImageIO.getImageReaders(imageStream).next();
        ImageReadParam param = reader.getDefaultReadParam();

        param.setSourceRegion(rect);
        reader.setInput(imageStream, true, true);
        BufferedImage image = reader.read(0, param);

        reader.dispose();
        imageStream.close();

        return image;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowUI();
            }
        });
    }
}

The result looks like this:

Answer 2

Generally, you'd need to do something like this:

• Break the image into manageable size image files and store them on disk with your application.
• When displaying a particular part of this image, only the load and display image fragments that overlap your viewport.
• As you pan around the image, update the loaded and displayed image fragments appropriately.
• Either let the unnecessary image fragments get collected by the GC or load new ones in such a way that they overwrite older ones. (This last argues for identically-sized image fragments that load into pooled memory buffers.)