图片通过文件流方式生成缩略图

　　　/// <summary>
        /// 按模板的方式生成缩略图（以流的方式获取文件）
        /// 生成缩略图函数
        /// </summary>
        /// <param name="fromFileStream">源图文件流</param>
        /// <param name="fileSaveUrl">缩略图存放地址</param>
        /// <param name="templateWidth">模板宽</param>
        /// <param name="templateHeight">模板高</param>
        public void MakeSmallImg(Stream fromFileStream, string fileSaveUrl, Double templateWidth, Double templateHeight)
        {
            //从文件取得图片对象，并使用流中嵌入颜色管理信息
            System.Drawing.Image myImage = System.Drawing.Image.FromStream(fromFileStream, true);
            Double newWidth = myImage.Width;
            Double newHeight = myImage.Height;
            if (newWidth > newHeight || newWidth == newHeight)
            {
                if (newWidth > templateWidth)
                {
                    newWidth = templateWidth;
                    newHeight = newHeight * (newWidth / myImage.Width);
                }
            }
            else
            {
                if (newHeight > templateHeight)
                {
                    newHeight = templateHeight;
                    newWidth = newHeight * (newHeight / myImage.Height);
                }
            }
            System.Drawing.Size mySize = new Size((int)newWidth, (int)newHeight);
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(mySize.Width, mySize.Height);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.Clear(Color.White);
            g.DrawImage(myImage, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height),
                new System.Drawing.Rectangle(0, 0, myImage.Width, myImage.Height),
                System.Drawing.GraphicsUnit.Pixel);

            bitmap.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
            g.Dispose();
            myImage.Dispose();
            bitmap.Dispose();
        }

　　　//调用方法

　　 protected void btnImg_Click(object sender, EventArgs e)
        {
            string path = Server.MapPath(@"image\12890012151.jpg");
            FileStream fs = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
            MakeSmallImg(fs, Server.MapPath(@"image\12890012151a.jpg"), 80, 80);
        }