生成缩略图和添加水印

using System.IO;
using System.Drawing.Imaging ;
using System.Drawing;

protected void Button1_Click(object sender, EventArgs e)
    {
            Graphics g=null;
            System.Drawing.Image upimage=null;
            System.Drawing.Image thumimg=null;
            System.Drawing.Image simage=null;
            Bitmap outputfile=null;
            try
            {
            string extension = Path.GetExtension(File1.PostedFile.FileName).ToUpper();
            string filename = DateTime.Now.ToString("yyyyMMddhhmmss");
            string smallpath = Server.MapPath(".")+"/smallimg/";
            string bigpath = Server.MapPath(".")+"/bigimg/";
            int width,height,newwidth,newheight;
            System.Drawing.Image.GetThumbnailImageAbort callb =new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);
            if(!Directory.Exists(smallpath))
            Directory.CreateDirectory(smallpath);
            if(!Directory.Exists(bigpath))
            Directory.CreateDirectory(bigpath);
            Stream upimgfile = File1.PostedFile.InputStream;
            string simagefile = Server.MapPath("Image/tu3.jpg"); //要加水印的文件
            simage=System.Drawing.Image.FromFile(simagefile);
            upimage= System.Drawing.Image.FromStream(upimgfile); //上传的图片
            width = upimage.Width;
            height = upimage.Height;
            if(width>height)
            {
            newwidth=200;
            newheight =(int)((double)height/(double)width * (double)newwidth);
            }
            else
            {
            newheight=200;
            newwidth=(int)((double)width/(double)height * (double)newheight);
            }
            thumimg = upimage.GetThumbnailImage(newwidth,newheight,callb,IntPtr.Zero);
            outputfile=new Bitmap(upimage);
            g=Graphics.FromImage(outputfile);
            g.DrawImage(simage,new Rectangle(upimage.Width-simage.Width,upimage.Height-simage.Height,upimage.Width,upimage.Height),0,0,upimage.Width,upimage.Height,GraphicsUnit.Pixel);
            string newpath = bigpath + filename + extension; //原始图路径
            string thumpath = smallpath + filename + extension; //缩略图路径
            outputfile.Save(newpath);
            thumimg.Save(thumpath);
            outputfile.Dispose();
            }
            catch(Exception ex)
            {
            throw ex;
            }
            finally
            {
            if(g!=null)
            g.Dispose();
            if(thumimg!=null)
            thumimg.Dispose();
            if(upimage!=null)
            upimage.Dispose();
            if(simage!=null)
            simage.Dispose();
            }
       }
       public bool ThumbnailCallback()
       {
              return false;
       }