C#產生縮圖,加文字或圖片浮水印

最近做東西,客戶要求上傳商品大圖,自動產生縮圖,要求等比縮放,正好能在指定的大小內顯示,(即如果高超出的比寬超出的多,就把高縮到指定高度,寬也等比縮放,反之寬也如此)
從網上找了如下代碼(出處不明),但發現他的產生縮圖的方式有四種,但都不是我想要的,於是在上面加了case "DB"://等比縮放（不變形，如果高大按高，寬大按寬縮放） 這種方式實現了我想要的功能
 /**/
    /// <summary>
    /// 產生縮圖
    /// </summary>
    /// <param name="originalImagePath">源圖路徑（實體路徑）</param>
    /// <param name="thumbnailPath">縮圖路徑（實體路徑）</param>
    /// <param name="width">縮圖寬度</param>
    /// <param name="height">縮圖高度</param>
    /// <param name="mode">產生縮圖的方式</param>
    public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode,string type)
    {
        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;
            case "DB"://等比縮放（不變形，如果高大按高，寬大按寬縮放）
                if ((double)originalImage.Width / (double)towidth < (double)originalImage.Height / (double)toheight)
                {
                    toheight = height;
                    towidth = originalImage.Width * height / originalImage.Height;
                }
                else
                {
                    towidth = width;
                    toheight = originalImage.Height * width / originalImage.Width;
                }
                break;
            default:
                break;
        }

        //建立一個bmp圖片
        System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

        //建立一個畫板
        System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);

        //設定高品質插值法
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

        //設定高品質,低速度呈現平滑程度
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

        //清空畫布並以透明背景色填充
        g.Clear(System.Drawing.Color.Transparent);

        //在指定位置並且按指定大小繪製原圖片的指定部分
        g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
        new System.Drawing.Rectangle(x, y, ow, oh),
        System.Drawing.GraphicsUnit.Pixel);

        try
        {
            //儲存縮圖
            if (type=="JPG")
            {
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            if (type=="BMP")
            {
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp);
            }
            if (type=="GIF")
            {
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
            }
            if (type=="PNG")
            {
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png);
            }
        }
        catch (System.Exception e)
        {
            throw e;
        }
        finally
        {
            originalImage.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }

    /**/
    /// <summary>
    /// 在圖片上增加文字浮水印
    /// </summary>
    /// <param name="Path">原伺服器圖片路徑</param>
    /// <param name="Path_sy">產生的帶文字浮水印的圖片路徑</param>
    protected void AddShuiYinWord(string Path, string Path_sy)
    {
        string addText = "測試浮水印";
        System.Drawing.Image image = System.Drawing.Image.FromFile(Path);
        System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);
        g.DrawImage(image, 0, 0, image.Width, image.Height);
        System.Drawing.Font f = new System.Drawing.Font("Verdana", 16);
        System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.Blue);

        g.DrawString(addText, f, b, 15, 15);
        g.Dispose();

        image.Save(Path_sy);
        image.Dispose();
    }

    /**/
    /// <summary>
    /// 在圖片上產生圖片浮水印
    /// </summary>
    /// <param name="Path">原伺服器圖片路徑</param>
    /// <param name="Path_syp">產生的帶圖片浮水印的圖片路徑</param>
    /// <param name="Path_sypf">浮水印圖片路徑</param>
    protected void AddShuiYinPic(string Path, string Path_syp, string Path_sypf)
    {
        System.Drawing.Image image = System.Drawing.Image.FromFile(Path);
        System.Drawing.Image copyImage = System.Drawing.Image.FromFile(Path_sypf);
        System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);
        g.DrawImage(copyImage, new System.Drawing.Rectangle(image.Width - copyImage.Width, image.Height - copyImage.Height, copyImage.Width, copyImage.Height), 0, 0, copyImage.Width, copyImage.Height, System.Drawing.GraphicsUnit.Pixel);
        g.Dispose();

        image.Save(Path_syp);
        image.Dispose();
    }