生成缩略图加水印文字(C#)

/// <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>
    /// <param name="PicTitle">生成缩略图的叠加的水印文字</param>
    ///
    public static void MakeThumbnail(string originalImagePath,
        string thumbnailPath,
        int width,
        int height,
        string mode,
        string PicTitle)
    {
        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);
        System.Drawing.Font f = new System.Drawing.Font("Verdana", 10);//字体
        System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.Red);//颜色
        g.DrawString(PicTitle, f, b, 300, 300);
        g.Dispose();
        try
        {
            //if (thumbnailPath.IndexOf("ch1_lbt") == 1)
            //{
            //保存缩略图
            //if (File.Exists(thumbnailPath))
            //{
               // File.Delete(thumbnailPath);
                //bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
            //}
            //else
            //{
                //bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);               
            //}
        }
        catch (System.Exception e)
        {
            throw e;
        }
        finally
        {
            originalImage.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }