C#生成縮略圖代碼

/// 生成縮略圖 
    /// </summary> 
    /// <param name="originalImagePath">源圖路徑</param> 
    /// <param name="thumbnailPath">縮略圖路徑</param> 
    /// <param name="width">縮略圖寬度</param> 
    /// <param name="height">縮略圖高度</param> 
    /// <param name="mode">生成縮略圖的方式:HW指定高寬縮放(可能變形);W指定寬，高按比例 H指定高，寬按比例 Cut指定高寬裁減(不變形)</param>　　 
    /// <param name="mode">要縮略圖保存的格式(gif,jpg,bmp,png) 為空或未知類型都視為jpg</param>　　 
    public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode, string imageType)
    {
        Image originalImage = 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"://指定高寬縮放（可能變形）　　　　　　　　 
                break;
            case "W"://指定寬，高按比例　　　　　　　　　　 
                toheight = originalImage.Height * width / originalImage.Width;
                break;
            case "H"://指定高，寬按比例 
                towidth = originalImage.Width * height / originalImage.Height;
                break;
            case "Cut"://指定高寬裁減（不變形）　　　　　　　　 
                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;
        }
        //新建一個bmp圖片 
        Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
        //新建一個畫板 
        Graphics g = System.Drawing.Graphics.FromImage(bitmap);
        //設置高質量插值法 
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
        //設置高質量,低速度呈現平滑程度 
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        //清空畫布并以透明背景色填充 
        g.Clear(Color.Transparent);
        //在指定位置并且按指定大小繪制原圖片的指定部分 
        g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
           new Rectangle(x, y, ow, oh),
           GraphicsUnit.Pixel);
        try
        {
            //以jpg格式保存縮略圖 
            switch (imageType.ToLower())
            {
                case "gif":
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
                    break;
                case "jpg":
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                    break;
                case "bmp":
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp);
                    break;
                case "png":
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png);
                    break;
                default:
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                    break;
            }
        }
        catch (System.Exception e)
        {
            throw e;
        }
        finally
        {
            originalImage.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }