Quick preview of jpeg using subsample

Question

Hey,
Consider that you have a folder with many "medium sized" JPEGs, let's say: 2MB, 500KB, or so...
You want to explore that folder, without loading all files into memory, but in the same time you want to see a small preview of each image file (just like windows thumbnails).
Loading every single jpeg will cost you a lot of memory... so here comes SourceSubsampling.
I use following lines for reading jpegs:
public Image CreateImageFromFile(File file) throws InterruptedException, IOException {
        ImageReader reader= (ImageReader)(ImageIO.getImageReadersByFormatName("jpeg").next());
        ImageReadParam param = reader.getDefaultReadParam();
        ImageInputStream iis = ImageIO.createImageInputStream(file);
        reader.setInput(iis,true);
        param.setSourceSubsampling(16,16, 0, 0);
        Image img=null;
        try {
             img = reader.read(0,param);
        } catch (Exception e) {System.out.println("Error read");
        return img;            
    }Before using this method... I have used a simpler way:
FileInputStream FI=new FileInputStream(file);
IMAGE_Cobai=Toolkit.getDefaultToolkit().createImage(FI);
The first issue was... Loading TIME. I got 500 ms for a 2.5MB. It is acceptable for a single file, but for 10 or 100?!
The second issue was MEMORY. BufferedImage ate a lot of memory, sometimes I got some errors for exceeding max memory allocated for JVM (80MB or?!)
I solved the second, using first method (subsampling).
I wonder why the LOADING TIME is the same?
Is there any way to speed it up?* I thought that using setSourceSubsampling will force reader to simply ignore most of pixels and maybe read only one pixel for every 16x16 block.
It should be possible because comercial products like ACDSEE use these tricks for preview. Strange thing is I didn't find any library for java...
If you have some answers... pls write them here. I googled a lot... last 2-3 weeks.
Thx.

Answer 1

I posted a reply here that might help - see the post on 2008-06-06:
http://today.java.net/pub/a/today/2007/04/03/perils-of-image-getscaledinstance.html?page=last#thread