/// summary>
 /// 生成图片缩率图Action
 /// /summary>
 /// param name="p">原图url/param>
 /// param name="id">图片尺寸以及生成缩率图的类型/param>
 /// returns>/returns>
 [ValidateInput(false)]
 public ActionResult Index(string p, string id)
 {
  if (string.IsNullOrEmpty(p))
  {
  return new HttpStatusCodeResult(404);
  }

  string oPath = Regex.Replace(p, @"http[s]?://(.*?)/", "/", RegexOptions.IgnoreCase);
  int? oWidth = 200, oHeight = 200;
  int cutMode = 3;
  string pPath;
  string oDir;

  if (!string.IsNullOrEmpty(id))
  {
  string[] ss = id.Split(new char[] { '_' }, StringSplitOptions.RemoveEmptyEntries);
  if (ss.Length  2)
  {
   return new HttpStatusCodeResult(404);
  }
  if (ss.Length > 2)
  {
   cutMode = int.Parse(ss[2]);
  }
  oPath = oPath.Insert(oPath.LastIndexOf('/') + 1, string.Format("{0}_{1}_{2}_", ss[0], ss[1], cutMode));
  oWidth = int.Parse(ss[0]);
  oHeight = int.Parse(ss[1]);
  }

  pPath = Server.MapPath(oPath);
  oDir = Path.GetDirectoryName(pPath);

  if (!System.IO.File.Exists(pPath))
  {
  byte[] imagebytes = FileHelper.DownLoadFile(p);
  if (!Directory.Exists(oDir))
  {
   Directory.CreateDirectory(oDir);
  }
  FileHelper.MakeThumbnail(FileHelper.BytToImg(imagebytes), oWidth.Value, oHeight.Value, (ThumbnailMode)cutMode, pPath, true);
  }

  return File(pPath, FileHelper.GetContentTypeByExtension(Path.GetExtension(pPath).ToLower()));
 }

 public class FileHelper
 {
  /// summary>
 /// 图片后缀和ContentType对应字典
 /// /summary>
 static Dictionarystring, string> extensionContentTypeDic;

 static FileHelper()
 {
  if (extensionContentTypeDic == null)
  {
  //.jpg", ".png", ".gif", ".jpeg
  extensionContentTypeDic = new Dictionarystring, string>();
  extensionContentTypeDic.Add(".jpg", "image/jpeg");
  extensionContentTypeDic.Add(".png", "image/png");
  extensionContentTypeDic.Add(".gif", "image/gif");
  extensionContentTypeDic.Add(".jpeg", "image/jpeg");
  }
 }
 /// summary>
 /// 根据后缀名获取extension
 /// /summary>
 /// param name="extension">/param>
 /// returns>/returns>
 public static string GetContentTypeByExtension(string extension)
 {
  if (extensionContentTypeDic.ContainsKey(extension))
  {
  return extensionContentTypeDic[extension];
  }
  return null;
 }

 /// summary > 
 /// 将Image对象转化成二进制流 
 /// /summary > 
 /// param name="image" > /param > 
 /// returns > /returns > 
 public static byte[] ImageToByteArray(Image image)
 {
  MemoryStream imageStream = new MemoryStream();
  Bitmap bmp = new Bitmap(image.Width, image.Height);
  Graphics g = Graphics.FromImage(bmp);
  g.DrawImage(image, new System.Drawing.Rectangle(0, 0, image.Width, image.Height));
  try
  {
  bmp.Save(imageStream, image.RawFormat);
  }
  catch (Exception e)
  {

  bmp.Save(imageStream, System.Drawing.Imaging.ImageFormat.Jpeg);
  }
  byte[] byteImg = imageStream.GetBuffer();
  bmp.Dispose();
  g.Dispose();
  imageStream.Close();
  return byteImg;
 }

 /// summary> 
 /// 字节流转换成图片 
 /// /summary> 
 /// param name="byt">要转换的字节流/param> 
 /// returns>转换得到的Image对象/returns> 
 public static Image BytToImg(byte[] byt)
 {
  MemoryStream ms = new MemoryStream(byt);
  Image img = Image.FromStream(ms);
  ms.Close();
  return img;
 }

 /// summary>
 /// 生成缩率图
 /// /summary>
 /// param name="originalImage">原始图片Image/param>
 /// param name="width">缩率图宽/param>
 /// param name="height">缩率图高/param>
 /// param name="mode">生成缩率图的方式/param>
 /// param name="thumbnailPath">缩率图存放的地址/param>
 public static Image MakeThumbnail(Image originalImage, int width, int height, ThumbnailMode mode, string thumbnailPath, bool isSave = true)
 {
  int towidth = width;
  int toheight = height;

  int x = 0;
  int y = 0;
  int ow = originalImage.Width;
  int oh = originalImage.Height;
  switch (mode)
  {
  case ThumbnailMode.HW://指定高宽缩放（可能变形）   
   break;
  case ThumbnailMode.W://指定宽，高按比例   
   toheight = originalImage.Height * width / originalImage.Width;
   break;
  case ThumbnailMode.H://指定高，宽按比例 
   towidth = originalImage.Width * height / originalImage.Height;
   break;
  case ThumbnailMode.Cut://指定高宽裁减（不变形）   
   if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
   {
   oh = originalImage.Height;
   ow = originalImage.Height * towidth / toheight;
   y = 0;
   x = (originalImage.Width - ow) / 2;
   }
   else
   {
   ow = originalImage.Width;
   oh = originalImage.Width * height / towidth;
   x = 0;
   y = (originalImage.Height - oh) / 2;
   }
   break;

  default:
   break;
  }

  //新建一个bmp图片 
  System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
  //新建一个画板 
  Graphics g = System.Drawing.Graphics.FromImage(bitmap);
  //设置高质量插值法 
  g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
  //设置高质量,低速度呈现平滑程度 
  g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
  //清空画布并以透明背景色填充 
  g.Clear(Color.Transparent);
  //在指定位置并且按指定大小绘制原图片的指定部分 
  g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
  new Rectangle(x, y, ow, oh),
  GraphicsUnit.Pixel);
  if (!isSave)
  {
  return bitmap;
  }
  try
  {
  //以jpg格式保存缩略图 
  //bitmap.Save(thumbnailPath, bitmap.RawFormat);
  bitmap.Save(thumbnailPath, ImageFormat.Jpeg);
  return bitmap;

  }
  catch (System.Exception e)
  {
  throw e;
  }
  finally
  {
  originalImage.Dispose();
  bitmap.Dispose();
  g.Dispose();
  }
  return null;
 }


 /// summary>
 /// 下载指定文件
 /// /summary>
 /// param name="remoteUrl">/param>
 /// param name="ss">/param>
 public static byte[] DownLoadFile(string remoteUrl)
 {
  WebClient wc = new WebClient();
  try
  {
  return wc.DownloadData(remoteUrl);
  }
  catch (Exception e)
  {
  throw new Exception("下载文件失败");
  }
 }

 }

 public enum ThumbnailMode
 {
 /// summary>
 /// 指定高宽缩放（可能变形）
 /// /summary>
 HW,
 /// summary>
 /// 指定高，宽按比例
 /// /summary>
 H,
 /// summary>
 /// 指定宽，高按比例
 /// /summary>
 W,
 /// summary>
 /// 指定高宽裁减（不变形） 
 /// /summary>
 Cut,

 }