/// <summary>
  /// asp.net上传图片并生成缩略图
  /// </summary>
  /// <param name="upImage">HtmlInputFile控件</param>
  /// <param name="sSavePath">保存的路径,些为相对服务器路径的下的文件夹</param>
  /// <param name="sThumbExtension">缩略图的thumb</param>
  /// <param name="intThumbWidth">生成缩略图的宽度</param>
  /// <param name="intThumbHeight">生成缩略图的高度</param>
  /// <returns>缩略图名称</returns>
  public string UpLoadImage(HtmlInputFile upImage, string sSavePath, string sThumbExtension, int intThumbWidth, int intThumbHeight)
  {
   string sThumbFile = "";
   string sFilename = "";  
   if (upImage.PostedFile != null)
   {
    HttpPostedFile myFile = upImage.PostedFile;
    int nFileLen = myFile.ContentLength;
    if (nFileLen == 0)
     return "没有选择上传图片";   
    //获取upImage选择文件的扩展名
    string extendName = System.IO.Path.GetExtension(myFile.FileName).ToLower();
    //判断是否为图片格式
    if (extendName != ".jpg" && extendName != ".jpge" && extendName != ".gif" && extendName != ".bmp" && extendName != ".png")
     return "图片格式不正确";
    
    byte[] myData = new Byte[nFileLen];
    myFile.InputStream.Read(myData, 0, nFileLen);
    sFilename = System.IO.Path.GetFileName(myFile.FileName);
    int file_append = 0;
    //检查当前文件夹下是否有同名图片,有则在文件名+1
    while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename)))
    {
     file_append++;
     sFilename = System.IO.Path.GetFileNameWithoutExtension(myFile.FileName)
      + file_append.ToString() + extendName;
    }
    System.IO.FileStream newFile
     = new System.IO.FileStream(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename),
     System.IO.FileMode.Create, System.IO.FileAccess.Write);
    newFile.Write(myData, 0, myData.Length);
    newFile.Close();
    //以上为上传原图
    try
    {
     //原图加载
     using (System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename)))
     {
      //原图宽度和高度
      int width = sourceImage.Width;
      int height = sourceImage.Height;
      int smallWidth;
      int smallHeight;
      //获取第一张绘制图的大小,(比较 原图的宽/缩略图的宽 和 原图的高/缩略图的高)
      if (((decimal)width) / height <= ((decimal)intThumbWidth) / intThumbHeight)
      {
       smallWidth = intThumbWidth;
       smallHeight = intThumbWidth * height / width;
      }
      else
      {
       smallWidth = intThumbHeight * width / height;
       smallHeight = intThumbHeight;
      }
      //判断缩略图在当前文件夹下是否同名称文件存在
      file_append = 0;
      sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) + extendName;
      while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sThumbFile)))
      {
       file_append++;
       sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) +
        file_append.ToString() + extendName;
      }
      //缩略图保存的绝对路径
      string smallImagePath = System.Web.HttpContext.Current.Server.MapPath(sSavePath) + sThumbFile;
      //新建一个图板,以最小等比例压缩大小绘制原图
      using (System.Drawing.Image bitmap = new System.Drawing.Bitmap(smallWidth, smallHeight))
      {
       //绘制中间图
       using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap))
       {
        //高清,平滑
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        g.Clear(Color.Black);
        g.DrawImage(
        sourceImage,
        new System.Drawing.Rectangle(0, 0, smallWidth, smallHeight),
        new System.Drawing.Rectangle(0, 0, width, height),
        System.Drawing.GraphicsUnit.Pixel
        );
       }
       //新建一个图板,以缩略图大小绘制中间图
       using (System.Drawing.Image bitmap1 = new System.Drawing.Bitmap(intThumbWidth, intThumbHeight))
       {
      //绘制缩略图 http://www.cnblogs.com/sosoft/
        using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap1))
        {
         //高清,平滑
         g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
         g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
         g.Clear(Color.Black);
         int lwidth = (smallWidth - intThumbWidth) / 2;
         int bheight = (smallHeight - intThumbHeight) / 2;
         g.DrawImage(bitmap, new Rectangle(0, 0, intThumbWidth, intThumbHeight), lwidth, bheight, intThumbWidth, intThumbHeight, GraphicsUnit.Pixel);
         g.Dispose();
         bitmap1.Save(smallImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
       }
      }
     }
    }
    catch
    {
     //出错则删除
     System.IO.File.Delete(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename));
     return "图片格式不正确";
    }
    //返回缩略图名称
    return sThumbFile;
   }
   return "没有选择图片";
  }

 <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml" >
 <head runat="server">
  <title>图片上传-柯乐义</title>
 </head>
 <body>
  <form id="form1" runat="server">
  <div>  
   <input id="File1" runat="server" type="file" /></div><asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
  </form>
 </body>
 </html>

 protected void Button1_Click(object sender, EventArgs e)
  {
   string a = this.UpLoadImage(this.File1, "UpLoad/", "thumb_", 118, 118); 
  }