/// <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 1、HW:指定高宽缩放（可能变形）2、W：指定宽，高按比例 3、H：指定高，宽按比例 4、Cut：指定高宽裁减（不变形）</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();

            }

        }