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    /// <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.Drawing.Drawing2D.SmoothingMode.HighQuality;
 
        //清空画布并以透明背景色填充
        g.Clear(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 Rectangle(0, 0, towidth, toheight),
            new Rectangle(x, y, ow, oh),
            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();
        }
    }