asp.net上传图片并同时生成缩略图

using System; 
using System.Data; 
using System.Configuration; 
using System.Collections; 
using System.Web; 
using System.Web.Security; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
using System.Drawing; 
public partial class slt_Default : System.Web.UI.Page 
{ 
    protected void Page_Load(object sender, EventArgs e) 
    { 
    } 
    protected void bt_upload_Click(object sender, EventArgs e) 
    { 
        //检查上传文件的格式是否有效  
        if (this.UploadFile.PostedFile.ContentType.ToLower().IndexOf("image") < 0) 
        { 
            Response.Write("上传图片格式无效！"); 
            return; 
        } 
        //生成原图  
        Byte[] oFileByte = new byte[this.UploadFile.PostedFile.ContentLength]; 
        System.IO.Stream oStream = this.UploadFile.PostedFile.InputStream; 
        System.Drawing.Image oImage = System.Drawing.Image.FromStream(oStream); 
        int oWidth = oImage.Width; //原图宽度  
        int oHeight = oImage.Height; //原图高度  
        int tWidth = 100; //设置缩略图初始宽度  
        int tHeight = 100; //设置缩略图初始高度 
        //按比例计算出缩略图的宽度和高度  
        if (oWidth >= oHeight) 
        { 
            tHeight = (int)Math.Floor(Convert.ToDouble(oHeight) * (Convert.ToDouble(tWidth) / Convert.ToDouble(oWidth))); 
        } 
        else 
        { 
            tWidth = (int)Math.Floor(Convert.ToDouble(oWidth) * (Convert.ToDouble(tHeight) / Convert.ToDouble(oHeight))); 
        } 
        //生成缩略原图