网站中的缩略图是如何生成的？（C#处理图像）

 网站中的缩略图是如何生成的？（C#处理图像）

controller层代码：

/// <summary>
        /// 生成缩略图
        /// </summary>
        /// <returns></returns>
        public ActionResult ThumImg()
        {

            Response.Clear();
            //string originalFileName = Server.MapPath(Request.QueryString["fn"]); //服务器上的目录名
            string originalFileName = Request.QueryString["fn"];//本地目录名
            int thumbnailWidth = Convert.ToInt16(Request.QueryString["tw"]);
            int thumbnailHeight = Convert.ToInt16(Request.QueryString["th"]);
            string bgColorString = Convert.ToString(Request.QueryString["bg"]);
            new ThumImage(originalFileName, thumbnailWidth, thumbnailHeight, bgColorString).ThumImg();
            return View();
        }

    }

VIEW层代码：

   <%int j=0;
        foreach (var i in ViewData["ImgList"] as List<string>)
      {
          j++;
          if (j > 20) break;
             %>
    <img src='/product/ThumImg?fn=<%=i %>&tw=50&th=50&bg=000000' border="0">
    <%} %>

Coder层代码：

 public class ThumImage
    {
        string originalFileName;
        int thumbnailWidth;
        int thumbnailHeight;
        string bgColorString;
        public ThumImage(string _originalFileName, int _thumbnailWidth, int _thumbnailHeight, string _bgColorString)
        {
            this.originalFileName = _originalFileName;
            this.thumbnailWidth = _thumbnailWidth;
            this.thumbnailHeight = _thumbnailHeight;
            this.bgColorString = _bgColorString;
        }
        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <returns></returns>
        public void ThumImg()
        {

            HttpContext.Current.Response.Clear();
            #region 建立图像主体对象
            ColorConverter cv = new ColorConverter();
            Color bgColor = (Color)cv.ConvertFromString("#" + bgColorString);//通过string，生成一个color对象，ColorConverter是颜色转换方法
            System.Drawing.Image img = System.Drawing.Image.FromFile(originalFileName);//通过url得到image对象
            System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;//指定文件的文件格式,它是ImageFormat类型,不可承继
            System.Drawing.Size newSize = this.GetNewSize(thumbnailWidth, thumbnailHeight, img.Width, img.Height);//图像尺寸，GetNewSize实现等比例缩放
            System.Drawing.Bitmap outBmp = new Bitmap(thumbnailWidth, thumbnailHeight);//建立一个封闭GDI+ 位图对象
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(outBmp);//建立一个GDI+ 位图画面,从指定的Image对象中
            #endregion

            #region 设置画布的描绘质量
            g.CompositingQuality = CompositingQuality.Default;
            g.SmoothingMode = SmoothingMode.Default;
            g.InterpolationMode = InterpolationMode.Default;
            g.Clear(bgColor);
            Rectangle r = new Rectangle((thumbnailWidth - newSize.Width) / 2,
                                           (thumbnailHeight - newSize.Height) / 2,
                                           newSize.Width, newSize.Height);
            g.DrawImage(img, r, 0, 0, img.Width, img.Height, GraphicsUnit.Pixel);
            g.Dispose();
            #endregion

            #region 设置服务器响应文件头类型
            if (thisFormat.Equals(System.Drawing.Imaging.ImageFormat.Gif))
            {
                HttpContext.Current.Response.ContentType = "image/gif";//网页内容类型为图像的MIME
            }
            else
            {
                HttpContext.Current.Response.ContentType = "image/jpeg";
            }
            #endregion

 

            //设置压缩质量
            System.Drawing.Imaging.EncoderParameters encoderParams = new EncoderParameters();
            System.Drawing.Imaging.EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, new long[] { 100 });
            encoderParams.Param[0] = encoderParam;

            //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
            System.Drawing.Imaging.ImageCodecInfo[] arrayICI = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
            System.Drawing.Imaging.ImageCodecInfo jpegICI = null;

            for (int fwd = 0; fwd < arrayICI.Length; fwd++)
            {
                if (arrayICI[fwd].FormatDescription.Equals("JPEG"))
                {
                    jpegICI = arrayICI[fwd];
                    break;
                }
            }

            if (jpegICI == null)
            {
                outBmp.Save(HttpContext.Current.Response.OutputStream, jpegICI, encoderParams);
            }
            else
            {
                outBmp.Save(HttpContext.Current.Response.OutputStream, thisFormat); //保存的页面的输出流中
            }
        }

        /// <summary>
        /// 图像根据相应尺寸实现等比例缩放
        /// </summary>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        /// <param name="width"></param>
        /// <param name="height"></param>
        /// <returns></returns>
        System.Drawing.Size GetNewSize(int maxWidth, int maxHeight, int width, int height)
        {
            Double w = 0.0;
            Double h = 0.0;
            Double sw = Convert.ToDouble(width);
            Double sh = Convert.ToDouble(height);
            Double mw = Convert.ToDouble(maxWidth);
            Double mh = Convert.ToDouble(maxHeight);

            if (sw < mw && sh < mh)
            {
                w = sw;
                h = sh;
            }
            else if ((sw / sh) > (mw / mh))
            {
                w = maxWidth;
                h = (w * sh) / sw;
            }
            else
            {
                h = maxHeight;
                w = (h * sw) / sh;
            }
            return new System.Drawing.Size(Convert.ToInt32(w), Convert.ToInt32(h));
        }

    }