Memory Efficiency of BufferedImage and ImageIO

Question

This thread discusses the memory efficiency of BufferedImage and ImageIO. I also like to know whether if there's possible memory leak in BufferedImage / ImageIO, or just that the result matches the specifications. Any comments are welcomed.
My project uses a servlet to create appropriate image tiles (in PNG format) that fits the specification of google map, from images stored in a database. But it only takes a few images to make the system out of heap memory. Increasing the initial heap memory just delays the problem. So it is not acceptable.
To understand why that happens, I write a simple code to check the memory usage of BufferedImage and ImageIO. The code simply keeps making byte arrays from the same image until it is running out of the heap memory.
Below shows how many byte arrays it can create:
1M jpeg picture (2560*1920):
jpeg = 123
png = 3
318K png picture (1000*900):
jpeg = 1420
png = 178
Notice that the program runs out of memory with only 3 PNG byte arrays for the first picture!!!! Is this normal???
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.awt.geom.*;
import javax.imageio.*;
import java.io.*;
import javax.swing.*;
import java.util.*;
public class Test {
     public static void main(String[] args) {
          Collection images = new ArrayList();
          for (;;) {
               try {
                    BufferedImage img = ImageIO.read(new File("PTHNWIDE.png"));
                    img.flush();
                    ByteArrayOutputStream out =
                         new ByteArrayOutputStream();
                    ImageIO.write(img, "png", out); // change to "jpeg" for jpeg
                    images.add(out.toByteArray());
                    out.close();
               } catch (OutOfMemoryError ome) {
                    System.err.println(images.size());
                    throw ome;
               } catch (Exception exc) {
                    exc.printStackTrace();
                    System.err.println(images.size());
}

Answer 1

a_silent_lamb wrote:
1. For the testing program, I just use the default VM setting, ie. 64M memory so it can run out faster. For server, the memory would be at least 256M.You might want to increase the heap size.
2. Do you mean it's 2560*1920*24bits when loaded? Of course.
That's pretty (too) large for my server usage, Well you have lots of image data
because it will need to process large dimension pictures (splitting each into set of 256*256 images). Anyway to be more efficient?Sure, use less colors :)