.NET将图片URL地址生成一个缩略图 - 路一直在

        public void MakeThumbnail(string imgPath_old, int width, int height)
        {

            System.Drawing.Image img = System.Drawing.Image.FromStream(new System.IO.MemoryStream(System.IO.File.ReadAllBytes(imgPath_old)));

            int towidth = width; int toheight = height;
            int x = 0; int y = 0; int ow = img.Width;
            int oh = img.Height;
            // 按值较大的进行等比缩放（不变形）  
            if ((double)img.Width / (double)towidth < (double)img.Height / (double)toheight)
            {
                toheight = height;
                towidth = img.Width * height / img.Height;
            }
            else
            {
                towidth = width;
                toheight = img.Height * width / img.Width;
            }
            //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(img, new System.Drawing.Rectangle(0, 0, towidth, toheight),
            new System.Drawing.Rectangle(x, y, ow, oh),
            System.Drawing.GraphicsUnit.Pixel);

            bitmap.Save(imgPath_old, System.Drawing.Imaging.ImageFormat.Jpeg);
            bitmap.Dispose();
            img.Dispose();
            g.Dispose();
        }

        protected void Page_Load(object sender, EventArgs e)
        {
            String filePath = Server.MapPath("~/xxx.jpg");
            new WebClient().DownloadFile("http://xxx/xxx.jpg", filePath);
            MakeThumbnail(filePath, 100, 100);
        }