按比例显示图片大小

ShowImage.aspx显示页面DataList模板项html:

<ItemTemplate>
       <asp:HyperLink id=HyperLink1 Target="_blank" NavigateUrl='<%# DataBinder.Eval(Container, "DataItem.filename", "images/{0}") %>' Runat="server">
        <asp:Image id=Image2 runat="server" ImageUrl='<%# "GetThumbnail.aspx?filename=" + Server.UrlEncode(DataBinder.Eval(Container, "DataItem.filename").ToString()) %>' AlternateText='<%# "文件名称:" + DataBinder.Eval(Container, "DataItem.filename") + "\n文件尺寸:" + DataBinder.Eval(Container, "DataItem.size") + " bytes" %>'>
        </asp:Image>
       </asp:HyperLink>
       <asp:Button id="Button1" onclick="HHH" runat="server" Text="Button"></asp:Button>
 </ItemTemplate>


图片处理页面GetThumbnail.aspx代码:
  const int MaxLength=150;  //显示图片最大长度

  private void Page_Load(object sender, System.EventArgs e)
  {
   if (Request.QueryString["filename"] != null)
   {
    //取得原图
    string filename=Request.QueryString["filename"];
    Bitmap bmpOld= new Bitmap(Server.MapPath("images/" + filename));

    //计算缩小比例
    double d1;
    if (bmpOld.Height>bmpOld.Width)
    d1=(double)(MaxLength/(double)bmpOld.Height);     
     else
     d1=(double)(MaxLength/(double)bmpOld.Width);

    //产生缩图
    Bitmap bmpThumb= new Bitmap(bmpOld,(int)(bmpOld.Width*d1),(int)(bmpOld.Height*d1));

    // 清除缓冲
    Response.Clear();
    //生成图片
    bmpThumb.Save(Response.OutputStream, ImageFormat.Jpeg);
    Response.End();
    //释放资源
    bmpThumb.Dispose();
    bmpOld.Dispose();
   }
  }