Image :: alpha / write jpg

public class ImageUtil
{
   public static void makeTransparant(BufferedImage img)
   {
      Graphics2D g = img.createGraphics();
      g.setComposite(AlphaComposite.getInstance(AlphaComposite.CLEAR, 0.0f));
      g.fillRect(0, 0, img.getWidth(), img.getHeight());
      g.dispose();
   }

   public static void writeJPG(BufferedImage img, File file, float quality) throws IOException
   {
      Iterator iter = ImageIO.getImageWritersByFormatName("jpeg");
      ImageWriter writer = iter.next();
      ImageWriteParam iwp = writer.getDefaultWriteParam();
      iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
      iwp.setCompressionQuality(quality);

      FileImageOutputStream output = new FileImageOutputStream(file);
      writer.setOutput(output);
      IIOImage image = new IIOImage(img, null, null);
      writer.write(null, image, iwp);
      writer.dispose();
      output.close();
   }
}