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") < 0)
        {
            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 = 140;//设置缩略图初始高度
        int toheight = 140;//设置缩略图初始宽度
        int x = 0;
        int y = 0;
        int ow = oImage.Width;
        int oh = oImage.Height;

        if (ow == 640 && ow == 640)
        {
            //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 = 0;
                x = (oImage.Width - ow) / 2;
            }
            else
            {
                ow = oImage.Width;
                oh = oImage.Width * toheight / towidth;
                x = 0;
                y = (oImage.Height - oh) / 2;
            }
            //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(0, 0, towidth, toheight), new Rectangle(0, 0, 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(".") == -1)
            return "";
        string[] temp = fileName.Split('.');
        return temp[temp.Length - 1].ToLower();
    }
    #endregion
}