批量修改圖片以及加水印

    {
        /// <summary>
        /// 生成縮略圖
        /// </summary>
        /// <param name="originalImagePath">源圖路徑（物理路徑）</param>
        /// <param name="thumbnailPath">縮略圖路徑（物理路徑）</param>
        /// <param name="width">縮略圖寬度</param>
        /// <param name="height">縮略圖高度</param>
        /// <param name="mode">生成縮略圖的方式</param>
        /// <param name="type">縮略圖的圖片類型</param>
        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode, string type)
        {
            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"://指定高寬縮放（可能變形）
                    break;
                case "W"://指定寬，高按比例
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，寬按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高寬裁減（不變形）
                    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;
                case "DB"://等比縮放（不變形，如果高大按高，寬大按寬縮放）
                    if ((double)originalImage.Width / (double)towidth < (double)originalImage.Height / (double)toheight)
                    {
                        toheight = height;
                        towidth = originalImage.Width * height / originalImage.Height;
                    }
                    else
                    {
                        towidth = width;
                        toheight = originalImage.Height * width / originalImage.Width;
                    }
                    break;
                default:
                    break;
            }

            //新建一個bmp圖片
            Image bitmap = new Bitmap(towidth, toheight);

            //新建一個畫板
            Graphics g = Graphics.FromImage(bitmap);

            //設置高質量插值法
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            //設置高質量,低速度呈現平滑程度
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //清空畫布並以透明背景色填充
            g.Clear(Color.Transparent);

            //在指定位置並且按指定大小繪制原圖片的指定部分
            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
            new Rectangle(x, y, ow, oh),
            GraphicsUnit.Pixel);

            try
            {
                //保存縮略圖
                if (type.ToUpper() == "JPG")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
                if (type.ToUpper() == "BMP")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp);
                }
                if (type.ToUpper() == "GIF")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
                }
                if (type.ToUpper() == "PNG")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png);
                }
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
        }}