asp.net 显示缩略图

//需引用的命名空间
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

  private void Page_Load(object sender, System.EventArgs e)
  {
   // 在此处放置用户代码以初始化页面
   Response.Clear() ;
   try
   {
    //需显示的图片的物理路径
    string originalFileName = Request["fn"].ToString();
    //需显示的图片的宽度
    int thumbnailWidth = Convert.ToInt32(Request["tw"]);
    //需显示的图片的高度
    int thumbnailHeight = Convert.ToInt32(Request["th"]);

    System.Drawing.Image img = System.Drawing.Image.FromFile(originalFileName);
    System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat ;
    System.Drawing.Size newSize = this.GetNewSize(thumbnailWidth,thumbnailHeight,img.Width,img.Height);
    System.Drawing.Bitmap outBmp = new Bitmap(thumbnailWidth,thumbnailHeight);
    System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(outBmp);
    
    g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality ;
    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear ;
    g.Clear(System.Drawing.Color.FromArgb(255,249,255,240));
    g.DrawImage(img,new Rectangle((thumbnailWidth-newSize.Width)/2,(thumbnailHeight-newSize.Height)/2,newSize.Width,newSize.Height),0,0,img.Width,img.Height,GraphicsUnit.Pixel);
    g.Dispose();

    if(thisFormat.Equals(System.Drawing.Imaging.ImageFormat.Gif))
     Response.ContentType = "image/gif";
    else
     Response.ContentType = "image.jpeg";

    System.Drawing.Imaging.EncoderParameters encoderParams = new EncoderParameters();
    long[] quality = new long[] {100};
    System.Drawing.Imaging.EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
    encoderParams.Param[0] = encoderParam;

    System.Drawing.Imaging.ImageCodecInfo[] arrayICI = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
    System.Drawing.Imaging.ImageCodecInfo jpegICI = null;
    for(int fwd=0;fwd<arrayICI.Length;fwd++)
    {
     if(arrayICI[fwd].FormatDescription.Equals("JPEG"))
     {
      jpegICI = arrayICI[fwd];
      break;
     }
    }
    if(jpegICI != null)
    {
     outBmp.Save(Response.OutputStream,jpegICI,encoderParams);
    }
    else
    {
     outBmp.Save(Response.OutputStream,thisFormat);
    }

   }
   catch(Exception err)
   {
   
   }

  }
  private System.Drawing.Size GetNewSize(int maxWidth, int maxHeight, int width, int height)
  {
   double w = 0.0;
   double h = 0.0;
   double sw = Convert.ToDouble(width);
   double sh = Convert.ToDouble(height);
   double mw = Convert.ToDouble(maxWidth);
   double mh = Convert.ToDouble(maxHeight);
   if(sw<mw && sh<mh)
   {
    w = sw;
    h = sh;
   }
   else if((sw/sh)>(mw/mh))
   {
    w = maxWidth;
    h = (w*sh)/sw;
   }
   else
   {
    h = maxHeight;
    w = (h*sw)/sh;
   }
   return new System.Drawing.Size(Convert.ToInt32(w),Convert.ToInt32(h));
  }