将BufferedImage转为指定的类型
File file = new File(filePath);
BufferedImage in = ImageIO.read(file);
BufferedImage newImage = new BufferedImage(
in.getWidth(), in.getHeight(), BufferedImage.TYPE_INT_ARGB);
Graphics2D g = newImage.createGraphics();
g.drawImage(in, 0, 0, null);
g.dispose();