(转)图像处理类（生成缩略图）

 　　/// <summary>
    /// 图像处理类
    /// </summary>
    public static class ImageHandler
    {
        /// <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>
        private static void MakeThumbnail(Stream PicStream, string thumbnailPath, int width, int height, string mode, string PicExtension)
        {
            System.Drawing.Image originalImage = System.Drawing.Image.FromStream(PicStream);
            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
            {
                //根据原来的图片格式，保存为原图片格式
                switch (PicExtension.ToLower())
                {
                    case "jpg":
                        //以jpg格式保存缩略图
                        bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                        break;
                    case "jpeg":
                        bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                        break;
                    case "pjpeg":
                        bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                        break;
                    case "gif":
                        bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
                        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();
            }
        }

        /// <summary>
        /// 通过FileUpload上传图片并压缩图片大小
        /// 四各形式：1)指定高 按比例缩放; 2)指定宽 按比例缩放; 3)不缩放; 4)指定宽高裁剪(不会变形).
        /// </summary>
        /// <param name="fu">FileUpload对象</param>
        /// <param name="file">文件完整路径Path</param>
        /// <param name="width">图片压缩后的宽度</param>
        /// <param name="height">图片压缩后的高度</param>
        /// <returns>返回文件存储的完整路径</returns>
        public static string SavePicture(FileUpload fu, string file, int width, int height)
        {
            Random myRd = new Random();
            string prefix = System.IO.Path.GetExtension(fu.FileName).ToLower();
            string fileName = "";
            if (prefix.Equals(".jpg") || prefix.Equals(".gif") || prefix.Equals(".jpeg") || prefix.Equals(".pjpeg") || prefix.Equals(".png") || prefix.Equals(".bmp"))
            {
                string strFileName = DateTime.Now.ToString("yyyyMMddHHmmss") + myRd.Next(1000) + prefix;
                string name = System.Web.HttpContext.Current.Server.MapPath(file + strFileName);
                fileName = HttpContext.Current.Server.MapPath(file);
                string filepath = HttpContext.Current.Server.MapPath("/");
                try
                {
                    //获取上传图片的大小
                    Stream PicStream = fu.PostedFile.InputStream;
                    MakeThumbnail(PicStream, fileName + strFileName, 500, 375, "HW", prefix);//指定高宽缩放（可能变形）         
                    if (width == 0 && height != 0)//指定高 按比例缩放
                    {
                        MakeThumbnail(PicStream, fileName + "small\\" + strFileName, width, height, "H", prefix);
                    }
                    else if (width != 0 && height == 0)//指定宽 按比例缩放
                    {
                        MakeThumbnail(PicStream, fileName + "small\\" + strFileName, width, height, "W", prefix);
                    }
                    else if (width == 0 && height == 0)//不缩放
                    {
                        fu.SaveAs(fileName + "small\\" + strFileName);
                    }
                    else//指定宽高裁剪(不会变形)
                    {
                        MakeThumbnail(PicStream, fileName + "small\\" + strFileName, width, height, "Cut", prefix);
                    }
                    //返回图片保存的路径
                    //fu.SaveAs(fileName + strFileName);//上传原图
                    return file + strFileName;
                }
                catch
                {
                    return null;
                }
            }
            else
            {
                return null;
            }
        }

        /// <summary>
        /// 创建文件夹
        /// </summary>
        /// <param name="directoryPath">文件夹路径</param>
        public static void CreatDirectory(string directoryPath)
        {
            try
            {
                DirectoryInfo dirInfo;
                string new_path = System.Web.HttpContext.Current.Server.MapPath(directoryPath);
                dirInfo = new DirectoryInfo(new_path);

                if (!dirInfo.Exists)
                {
                    dirInfo.Create();
                    System.IO.Directory.CreateDirectory(new_path);
                }
            }
            catch (System.Exception E)
            {
                throw E;
            }
        }
    }