サムネイル表示時の画像のサイズについて

protected void Page_Load(object sender, EventArgs e)
{
      CollectFiles(パス);

     DataList1.DataSource = CreateDataSource();
     DataList1.DataBind();
        :
}
private void CollectFiles(string path)
{
       // ファイル名を集める
       string filters = "*.jpg;*.png;*.gif";

       foreach (string filter in filters.Split(';'))
       {
          FileInfo[] fit = new DirectoryInfo(
                           this.Server.MapPath(path)).GetFiles(filter);     // "~/images"
       foreach (FileInfo fi in fit)
       {
           files.Add(fi);

       }
    }
}
protected void DataList1_ItemDataBound(object sender, DataListItemEventArgs e)
{
    string mei;

    if (files.Count > e.Item.ItemIndex)
        mei = IdData[0] + files[e.Item.ItemIndex].Name;
    else
       return;

    Control fc = e.Item.FindControl("Image6");
    if (fc != null)
    {
       ((Image)fc).ImageUrl = mei;
     }
     Control lb = e.Item.FindControl("Label6");
     if (lb != null)
      {
         ((Label)lb).Text = mei;
     }
  }
ICollection CreateDataSource()
{
     DataTable dt = new DataTable();
     DataRow dr;

     dt.Columns.Add(new DataColumn("StringValue1", typeof(string)));
     dt.Columns.Add(new DataColumn("StringValue2", typeof(string)));

     for (int i = 0; i < 9; i++)
     {
         dr = dt.NewRow();

         dr[0] = IdData[0] + files[0].Name;
        dr[1] = IdData[0] + files[0].Name;
         //dr[2] = 1.23 * (i + 1);

         dt.Rows.Add(dr);
     }

     DataView dv = new DataView(dt);

return dv;
}

System.Drawing.Image orig = System.Drawing.Image.FromFile(IdData[0] + "DSCF0001.jpg");

System.Drawing.Image thumbnail1 = CreateThumbnail1(orig, orig.Width / 20, orig.Height / 20);

thumbnail1.Save("thumbnail1.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);