java压缩图片 解决java压缩图片透明背景变黑色的问题

public class Picture { 
        // TODO Auto-generated constructor stub 
     public static void resizePNG(String fromFile, String toFile, int outputWidth, int outputHeight,boolean proportion) {
              try { 
               File f2 = new File(fromFile); 

                  BufferedImage bi2 = ImageIO.read(f2); 
               int newWidth;
              int newHeight;
           // 判断是否是等比缩放
           if (proportion == true) {
            // 为等比缩放计算输出的图片宽度及高度
            double rate1 = ((double) bi2.getWidth(null)) / (double) outputWidth + 0.1;
            double rate2 = ((double) bi2.getHeight(null)) / (double) outputHeight + 0.1;
            // 根据缩放比率大的进行缩放控制
            double rate = rate1 < rate2 ? rate1 : rate2;
            newWidth = (int) (((double) bi2.getWidth(null)) / rate);
            newHeight = (int) (((double) bi2.getHeight(null)) / rate);
           } else {
            newWidth = outputWidth; // 输出的图片宽度
            newHeight = outputHeight; // 输出的图片高度
           }
                  BufferedImage to = new BufferedImage(newWidth, newHeight, 

                          BufferedImage.TYPE_INT_RGB); 

                  Graphics2D g2d = to.createGraphics(); 

                  to = g2d.getDeviceConfiguration().createCompatibleImage(newWidth,newHeight, 

                          Transparency.TRANSLUCENT); 

                  g2d.dispose(); 

                  g2d = to.createGraphics(); 

                  Image from = bi2.getScaledInstance(newWidth, newHeight, bi2.SCALE_AREA_AVERAGING); 
                  g2d.drawImage(from, 0, 0, null);
                  g2d.dispose(); 

                  ImageIO.write(to, "png", new File(toFile)); 

              } catch (IOException e) { 

                  e.printStackTrace(); 

              } 

          } 

          public static void main(String[] args) throws IOException { 

              System.out.println("Start"); 

              resizePNG("C:\\Documents and Settings\\Administrator\\桌面\\8d9e9c82d158ccbf8b31059319d8bc3eb035414e.jpg", "C:\\Documents and Settings\\Administrator\\桌面\\ell.png",200, 100,true); 

              System.out.println("OK"); 

          } 
}