C# 生成指定大小缩略图

 /// <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)
    {
        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();
        }
    }

    /// <summary>
    /// 检测图片类型
    /// </summary>
    /// <param name="_fileExt"></param>
    /// <returns>正确返回True</returns>
    private bool CheckFileExt(string _fileExt)
    {
        string[] allowExt = new string[] { ".gif", ".jpg", ".jpeg" };
        for (int i = 0; i < allowExt.Length; i++)
        {
            if (allowExt[i] == _fileExt) { return true; }
        }
        return false;
    }

  var toFileName = Guid.NewGuid().ToString() + fileExt;
                var toFileFullPath = RouteHelp.GoodsSavePath + "\\";
                var viewPath = RouteHelp.GoodsImgUrl + "\\";
                var Title = File_Name;
                DirectoryInfo di = new DirectoryInfo(toFileFullPath);
                if (!di.Exists)
                {
                    di.Create();
                }
                string saveFile = toFileFullPath + "D" + toFileName;
                HttpFile.SaveAs(saveFile);

                //大缩略图
                string bigThumbPath = toFileFullPath + "X" + toFileName;
                MakeThumbnail(saveFile, bigThumbPath, 430, 430, "Cut ");
                //小缩略图
                string smallThumbPath = toFileFullPath + toFileName;
                MakeThumbnail(saveFile, smallThumbPath, 177, 177, "Cut ");