c#上传并改变图片大小

protected void UpLoadPhoto_Click(object sender, ImageClickEventArgs e)
    {
        if (FileUpload1.HasFile)
        {
            string fileContentType = FileUpload1.PostedFile.ContentType;
            if (fileContentType == "image/bmp" || fileContentType == "image/gif" || fileContentType == "image/pjpeg")
            {
                string name = FileUpload1.PostedFile.FileName; // 客户端文件路径 
                FileInfo file = new FileInfo(name);
                string fileName = file.Name; // 文件名称 
                string fileName_s = "s_" + file.Name; // 缩略图文件名称                 
                string webFilePath = Server.MapPath("file/" + fileName); // 服务器端文件路径 
                string webFilePath_s = Server.MapPath("file/" + fileName_s);　　// 服务器端缩略图路径 
                if (!File.Exists(webFilePath))
                {
                    try
                    {
                        FileUpload1.SaveAs(webFilePath); // 使用 SaveAs 方法保存文件 
                        MakeThumbnail(webFilePath, webFilePath_s, 100, 100, "Cut"); // 生成缩略图方法 
                        ScriptManager.RegisterStartupScript(UpdatePanel1, typeof(UpdatePanel), "scriptname", "alert('文件上传成功!')", true);
                        //this.RegisterStartupScript("hello", "<script>alert('文件上传成功!')</script>");
                        Tools.AddLog("0", "上传照片成功信息成功！");
                        imgPhoto.Visible = true;
                        imgPhoto.ImageUrl = webFilePath_s;
                        PhotoUrl = webFilePath_s;
                    }
                    catch (Exception ex)
                    {
                        Tools.AddLog("1", "上传照片成功信息失败！");
                        throw new Exception("提示：文件上传失败，失败原因" + ex.Message);
                    }
                }
                else
                {
                    this.RegisterStartupScript("hello", "<script>alert('图片已经存在，请重命名后上传!')</script>");
                }
            }
            else
            {
                this.RegisterStartupScript("hello", "<script>alert('文件类型不符!')</script>");
            }
        }
        else
        {
            ScriptManager.RegisterStartupScript(UpdatePanel1, typeof(UpdatePanel), "scriptname", "alert('请选择照片!')", true);
        }
    }
        /**/
    /// <summary> 
    /// 生成缩略图 
    /// </summary> 
    /// <param name="originalImagePath">源图路径（物理路径）</param> 
    /// <param name="thumbnailPath">缩略图路径（物理路径）</param> 
    /// <param name="width">缩略图宽度</param> 
    /// <param name="height">缩略图高度</param> 
    /// <param name="mode">生成缩略图的方式</param> 
    public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
    {
        System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);
 
        int towidth = width;
        int toheight = height;
 
        int x = 0;
        int y = 0;
        int ow = originalImage.Width;
        int oh = originalImage.Height;
 
        switch (mode)
        {
            case "HW"://指定高宽缩放（可能变形） 
                break;
            case "W"://指定宽，高按比例 
                toheight = originalImage.Height * width / originalImage.Width;
                break;
            case "H"://指定高，宽按比例 
                towidth = originalImage.Width * height / originalImage.Height;
                break;
            case "Cut"://指定高宽裁减（不变形） 
                if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                {
                    oh = originalImage.Height;
                    ow = originalImage.Height * towidth / toheight;
                    y = 0;
                    x = (originalImage.Width - ow) / 2;
                }
                else
                {
                    ow = originalImage.Width;
                    oh = originalImage.Width * height / towidth;
                    x = 0;
                    y = (originalImage.Height - oh) / 2;
                }
                break;
            default:
                break;
        }
 
        //新建一个bmp图片 
        System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
 
        //新建一个画板 
        System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
 
        //设置高质量插值法 
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
 
        //设置高质量,低速度呈现平滑程度 
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
 
        //清空画布并以透明背景色填充 
        g.Clear(System.Drawing.Color.Transparent);
 
        //在指定位置并且按指定大小绘制原图片的指定部分 
        g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
        new System.Drawing.Rectangle(x, y, ow, oh),
        System.Drawing.GraphicsUnit.Pixel);
 
        try
        {
            //以jpg格式保存缩略图 
            bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
        catch (System.Exception e)
        {
            throw e;
        }
        finally
        {
            originalImage.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }