code: public static void changeAlpha(String oldPath, String newPath, byte alpha) throws IOException {
          changeAlpha(new FileInputStream(oldPath), new FileOutputStream(newPath), alpha);
      }
docs: 更改图片alpha值
  
  @param oldPath 图片本地路径
  @param newPath 更改alpha值后的图片保存路径
  @param alpha   要设置的alpha值
  @throws IOException IOException