背景图片变透明

public class Alpha {
	public static  void transferAlpha(String imagePath,String outputDir,String outputFileName) throws Exception {
		Image image=ImageIO.read(new File(imagePath));
		ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
		try {
			ImageIcon imageIcon = new ImageIcon(image);
			BufferedImage bufferedImage = new BufferedImage(
					imageIcon.getIconWidth(), imageIcon.getIconHeight(),
					BufferedImage.TYPE_4BYTE_ABGR);
			Graphics2D g2D = (Graphics2D) bufferedImage.getGraphics();
			g2D.drawImage(imageIcon.getImage(), 0, 0,
					imageIcon.getImageObserver());
			int alpha = 0;
			for (int j1 = bufferedImage.getMinY(); j1 < bufferedImage
					.getHeight(); j1++) {
				for (int j2 = bufferedImage.getMinX(); j2 < bufferedImage
						.getWidth(); j2++) {
					int rgb = bufferedImage.getRGB(j2, j1);
					int R = (rgb & 0xff0000) >> 16;
					int G = (rgb & 0xff00) >> 8;
					int B = (rgb & 0xff);
					if (((255 - R) < 30) && ((255 - G) < 30)
							&& ((255 - B) < 30)) {
						rgb = ((alpha + 1) << 24) | (rgb & 0x00ffffff);
					}
					bufferedImage.setRGB(j2, j1, rgb);
				}
			}
			g2D.drawImage(bufferedImage, 0, 0, imageIcon.getImageObserver());
			new File(outputDir).mkdir();
			ImageIO.write(bufferedImage, "png", new File(outputDir+outputFileName));
			ImageIO.write(bufferedImage, "png", byteArrayOutputStream);
		} catch (Exception e) {
			e.printStackTrace();
		} finally {

		}
		//return byteArrayOutputStream.toByteArray();
	}