生成图片缩略图

        #region 图片缩放，多种指定方式生成图片
        /// <summary>
        /// 图片缩放
        /// </summary>
        /// <param name="originalImagePath">原始图片路径，如：c:\\images\\1.gif</param>
        /// <param name="thumbnailPath">生成缩略图图片路径，如：c:\\images\\2.gif</param>
        /// <param name="width">宽</param>
        /// <param name="height">高</param>
        /// <param name="mode">EQU：指定最大高宽等比例缩放；HW：//指定高宽缩放（可能变形）；W:指定宽，高按比例；H:指定高，宽按比例；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;

            if (mode == "EQU")//指定最大高宽，等比例缩放
            {
                //if(height/oh>width/ow),如果高比例多，按照宽来缩放；如果宽的比例多，按照高来缩放
                if (height * ow > width * oh)
                {
                    mode = "W";
                }
                else
                {
                    mode = "H";
                }
            }
            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();
            }
        }
        #endregion