关于分块上传图片的问题（客户段手机）

同志们我把一个Stream转换成string（是分段放的不是一次放完的）然后放到一个txt文件里等我把所有的Stream都放完成我想从这个txt文件中把我所放的东西提取出来生成图片咋办呢
protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            Stream tr = Request.InputStream;
            string FileNames = Request.QueryString["FileName"].ToString();
            StreamWriter writer;
            if (! File.Exists(Server.MapPath(@"Image/" + FileNames + ".txt")))
            {
                using (FileStream fstr = new FileStream(Server.MapPath(@"Image/" + FileNames + ".txt"), FileMode.Create)) ;
                StreamReader reader = new StreamReader(tr);
                writer = new StreamWriter(Server.MapPath(@"Image/" + FileNames + ".txt"));
                writer.Write(reader.ReadToEnd());
                writer.Flush();
                writer.Close();
                reader.Close();            }
            else
            {
                StreamReader reader = new StreamReader(tr);
                reader.Close();
            }
            File.WriteAllText(Server.MapPath(@"image/Log.txt"), File.ReadAllText(Server.MapPath(@"image/Log.txt")).ToString() + Request.QueryString["IsEnd"].ToString() + "(" + FileNames + ".txt)\r\n");            string IsEndC = Request.QueryString["IsEnd"].ToString();
            if (IsEndC == "1")
            {
                StreamReader imageReader = new StreamReader(Server.MapPath(@"Image/" + FileNames + ".txt"));
                System.Drawing.Image image = System.Drawing.Bitmap.FromStream(new MemoryStream(UnicodeEncoding.ASCII.GetBytes(imageReader.ReadToEnd())));
                System.Drawing.Bitmap bmap = new System.Drawing.Bitmap(image);
                MemoryStream mstr = new   MemoryStream();
                //bmap.Save(mstr, ImageFormat.Jpeg);
                FileStream fstr0 = new FileStream(Server.MapPath(@"Image/" + FileNames), FileMode.Create);
                mstr.WriteTo(fstr0);
                mstr.Close();
                fstr0.Close();
                //bmap.Dispose();
                fstr0.Dispose();               
                //FileStream fst0 = new FileStream(Server.MapPath(@"Image/" + FileNames), FileMode.OpenOrCreate);
                //fst0.Write(Str2Arr(imageReader), 0, Str2Arr(imageReader).Length);
                //fst0.Close();
                //fst0.Dispose();
                File.WriteAllText(Server.MapPath(@"image/Log.txt"), File.ReadAllText(Server.MapPath(@"image/Log.txt")).ToString() + imageReader.ReadToEnd().Length + "上传成功！(" + DateTime.Now.ToString() + ")\r\n");
            }
        }
        catch (Exception ex)
        {
            File.WriteAllText(Server.MapPath(@"image/Log.txt"), File.ReadAllText(Server.MapPath(@"image/Log.txt")).ToString()+ex.ToString() + "(" + DateTime.Now.ToString() + ")\r\n");
        }
    }