asp.net生成高质量缩略图通用函数(c#代码),支持多种生成方式

/// <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)
        {
            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
            Image bitmap = new System.Drawing.Bitmap(towidth,toheight);

            //新建一个画板
            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.Draw