上传大图的同时保存小图

protected void btnUpload_Click(object sender, EventArgs e)
        {
            if (FileUploadPic.HasFile)
            {
                string ext = Path.GetExtension(FileUploadPic.FileName).ToLower();
                if (ext == ".gif" || ext == ".jpg" || ext == ".jpeg" || ext == ".png")
                {
                    string pathBigImage = Server.MapPath("~/uploadImages/" + FileUploadPic.FileName);//获取大图的保存路径
                    FileUploadPic.SaveAs(pathBigImage);//保存大图

                   //获取缩略图并保存到指定路径
                    using (Bitmap myBitmap = new Bitmap(pathBigImage))
                    {
                        using (System.Drawing.Image myThumbnail = myBitmap.GetThumbnailImage(50, 50, new System.Drawing.Image.GetThumbnailImageAbort(delegate { return false; }), IntPtr.Zero))
                        {
                            myThumbnail.Save(Server.MapPath("~/smallImages/" + "_small" + FileUploadPic.FileName));
                        }
                    }

                    LiteralTip.Text = "上传成功！";
                }
                else
                {
                    ClientScript.RegisterStartupScript(GetType(),"警告","alert('文件类型错误，只允许上传jpg、jpeg、gif、png类型的图片！')",true);
                    return;
                }
            }
        }