Converting bitmap (byte[ ]) to PNG

Question

I have a BMP in a byte[ ] that I need to convert to a PNG. I get the byte[ ] from an external application thorugh JNI so there's nothing I can do about the format. The images will end up on a webpage so bitmaps are not acceptable due to size. Using some application (image editor, whatever) to convert the images won't do it as everything has to happen automagically.
I know that the incoming bitmap is correct as the following code produces a the expected bitmap in a file:
byte[] image = // code calling a method that gets the image goes here
try {
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        outStream.write(image, 0, image.length);
        FileOutputStream writer = new FileOutputStream("test.bmp");
        outStream.writeTo(writer);
         writer.close();
} catch (IOException e) {
       // error handling here
}I can't however figure out how to convert the bitmap to PNG. I'd prefer to do it directly from the byte[ ] but using a temporary BMP file is ok if it's easier.
I've tried to use the following code but it produces a 1kB black image of correct width and height.
    byte[] image = // code calling a method that gets the image goes here
    Image img = Toolkit.getDefaultToolkit().createImage(image); // returns a  sun.awt.windows.WImage
    int width = 100; //hardcoded at the moment as a I know the dimensions for the test images
    int height = 200;
    BufferedImage bImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
    Graphics2D g2d = bImage.createGraphics();
    g2d.drawImage(img, 0, 0, width, height, null);
    g2d.dispose();
    try {
        File outfile = new File("test.png");
        ImageIO.write(bi, "png", outfile);
    } catch (IOException e) {
        e.printStackTrace();
    }Could anyone provide some pointers?

Answer 1

When looking up ImageIcon I realized that both ImageIcon and Toolkit, which I was trying to use, only support reading GIF, JPG and PNG. Neither will help me as the data I have is in BMP format.
You'll need to create a conversion between the two fileformats yourself I was afraid of that, I really don't have the time to start fiddling around with file formats.
or find one somewhere,Oh well, back to Google. Any and all suggestions welcome.