C#上传图片同时生成缩略图，控制图片上传大小。

     #region 上传图片生成缩略图
     /// <summary>
     /// 上传图片
     /// </summary>
     /// <param name="sender"></param>
     /// <param name="e"></param>
     public void btnUpload_Click(object sender, EventArgs e)
     {
         //检查上传文件的格式是否有效
         if (this.fudPhoto.PostedFile.ContentType.ToLower().IndexOf("image") < )
         {
             Response.Write("<script>alert('上传图片格式无效!');window.location.href='LES_ApplyTopActivityAdd.aspx';</script>");
             return;
         }
         string FileNmae;
         string FileNameS;
         string name = fudPhoto.PostedFile.FileName;//客户端文件路径
         FileInfo file = new FileInfo(name);
         string fileName = file.Name;
         string ExtName = getFileExt(fileName).ToUpper();
         //生成原图
         Byte[] oFileByte = new byte[this.fudPhoto.PostedFile.ContentLength];
         System.IO.Stream oStream = this.fudPhoto.PostedFile.InputStream;
         System.Drawing.Image oImage = System.Drawing.Image.FromStream(oStream);
         int towidth = ;//设置缩略图初始高度
         int toheight = ;//设置缩略图初始宽度
         int x = ;
         int y = ;
         int ow = oImage.Width;
         int oh = oImage.Height;

         if (ow ==  && ow == )
         {
             //按比例计算出缩略图的宽度和高度 

             if (((double)oImage.Width / (double)oImage.Height) > ((double)towidth / (double)toheight))
             {
                 oh = oImage.Height;
                 ow = oImage.Height * towidth / toheight;
                 y = ;
                 x = (oImage.Width - ow) / ;
             }
             else
             {
                 ow = oImage.Width;
                 oh = oImage.Width * toheight / towidth;
                 x = ;
                 y = (oImage.Height - oh) / ;
             }
             //生成缩略原图
             Bitmap tImage = new Bitmap(towidth, toheight);
             Graphics g = Graphics.FromImage(tImage);
             g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; //设置高质量插值法
             g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;//设置高质量,低速度呈现平滑程度
             g.Clear(Color.Transparent); //清空画布并以透明背景色填充
             g.DrawImage(oImage, new Rectangle(, , towidth, toheight), new Rectangle(, , ow, oh), GraphicsUnit.Pixel);

             FileNmae = DateTime.Now.ToShortDateString().Replace("-", "") + DateTime.Now.Hour.ToString() + DateTime.Now.Minute.ToString() + DateTime.Now.Second.ToString() + DateTime.Now.Millisecond.ToString() + "." + ExtName; //保存原图的物理路径
             string oFullName = Server.MapPath("/uploadfiles//" + FileNmae);

             FileNameS = FileNmae + "-S" + ".JPG"; //保存缩略图的物理路径
             string tFullName = Server.MapPath("/uploadfiles//" + FileNameS);
             try
             {
                 //以JPG格式保存图片
                 oImage.Save(oFullName, System.Drawing.Imaging.ImageFormat.Jpeg);
                 tImage.Save(tFullName, System.Drawing.Imaging.ImageFormat.Jpeg);

                 //lbMessage.Text = "提示：文件”" + FileNmae + "“成功上传，并生成”" + FileNameS + "“缩略图，文件类型为：" +
                 //     fudPhoto.PostedFile.ContentType + "，文件大小为：" + fudPhoto.PostedFile.ContentLength + "B";
                 lbMessage.Text = "提示：文件成功上传，并生成”" + FileNameS + "“缩略图！";
                 string PIC = FileNmae;
                 ViewState["pic"] = PIC;
             }
             catch (Exception ex)
             {
                 throw ex;
             }
             finally
             {
                 //释放资源
                 oImage.Dispose();
                 g.Dispose();
                 tImage.Dispose();
             }
         }
         else
         {
             lbMessage.Text = "提示：图片的尺寸应该是640x640";
         }
     }
     private string getFileExt(string fileName)
     {
         if (fileName.IndexOf(".") == -)
             return "";
         string[] temp = fileName.Split('.');
         return temp[temp.Length - ].ToLower();
     }
     #endregion
 }
如图效果图：