/// <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();
        }
    } 

//var temp = url.Split('/');
        //string oldaddress = "~/Upload/images/" + temp[temp.Length - 1];
        //string newaddress = "~/Upload/images/SmallPic/" + temp[temp.Length - 1];
        ////添加缩略图
        //string filepath = Server.MapPath(oldaddress);
        ////if (System.IO.File.Exists(filepath))
        ////{
        ////    System.IO.File.Delete(filepath);
        ////}
        //string path1 = filepath;
        //string path2 = Server.MapPath(newaddress);
        //MakeThumbnail(path1, path2, 125, 95, "Hw");