asp.net生成缩略图示例方法分享

//调整图片大小

private static Size NewSize(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)//如果maxWidth和maxHeight大于源图像，则缩略图的长和高不变
            {
                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 Size(Convert.ToInt32(w), Convert.ToInt32(h));
        }

//生成缩略图

public static void SendSmallImage(string filename, string newfile, int maxHeight, int maxWidth, string mode)

        {

            System.Drawing.Image img = System.Drawing.Image.FromFile(filename);//源图像的信息

            System.Drawing.Imaging.ImageFormat thisformat = img.RawFormat; //源图像的格式

            Size newSize = NewSize(maxWidth, maxHeight, img.Width, img.Height); //返回调整后的图像Width与Height

            Bitmap outBmp = new Bitmap(maxWidth, maxHeight);

            Graphics g = Graphics.FromImage(outBmp);

            //设置画布的描绘质量

            g.CompositingQuality = CompositingQuality.HighQuality;

            g.SmoothingMode = SmoothingMode.HighQuality;

            g.InterpolationMode = InterpolationMode.HighQualityBicubic;

            g.Clear(Color.White);

            g.DrawImage(img, new Rectangle(((maxWidth - newSize.Width) / 2), ((maxHeight - newSize.Height) / 2), newSize.Width, newSize.Height), 0, 0, img.Width, img.Height, GraphicsUnit.Pixel);

            g.Dispose();

            //以下代码为保存图片时，设置压缩质量

            EncoderParameters encoderParams = new EncoderParameters();

            long[] quality = new long[1];

            quality[0] = 100;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);

            encoderParams.Param[0] = encoderParam;

            //获取包含有关内置图像编码解码器的信息的ImageCodecInfo对象。

            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();

            ImageCodecInfo jpegICI = null;

            for (int x = 0; x < arrayICI.Length; x++)

            {

                if (arrayICI[x].FormatDescription.Equals("JPEG"))

                {

                    jpegICI = arrayICI[x];//设置jpeg编码

                    break;

                }

            }

            if (jpegICI != null)

            {

                outBmp.Save(newfile, jpegICI, encoderParams);

            }

            else

            {

                outBmp.Save(newfile, thisformat);

            }

            img.Dispose();

            outBmp.Dispose();

        }

//输出图片

        public static void OutPutImg(string imgFilePath)

        {

            FileStream fs = new FileStream(HttpContext.Current.Server.MapPath(imgFilePath), FileMode.Open, FileAccess.Read);

            DateTime contentModified = System.IO.File.GetLastWriteTime(HttpContext.Current.Server.MapPath(imgFilePath));

            if (IsClientCached(contentModified))

            {

                HttpContext.Current.Response.StatusCode = 304;

                HttpContext.Current.Response.SuppressContent = true;

            }

            else

            {

                byte[] mydata = new byte[fs.Length];

                int Length = Convert.ToInt32(fs.Length);

                fs.Read(mydata, 0, Length);

                fs.Close();

                HttpContext.Current.Response.OutputStream.Write(mydata, 0, Length);

                HttpContext.Current.Response.ContentType = "image/jpeg";

                HttpContext.Current.Response.End();

                HttpContext.Current.Response.Cache.SetETagFromFileDependencies();

                HttpContext.Current.Response.Cache.SetAllowResponseInBrowserHistory(true);

                HttpContext.Current.Response.Cache.SetLastModified(contentModified);

            }

        }

//outpuimg.ashx?src=/images/weimeidesc/8af30049-797e-4eb4-8a54-cc4de47c1694.jpg!100x100.jpg

        public void ProcessRequest(HttpContext context)

        {

            //获取图片

            string imgUrl = context.Request.QueryString["src"];

            string trueFilePath = imgUrl.Split('!')[0];

            //获取图片大小

            int width = Convert.ToInt32(imgUrl.Split('!')[1].Replace(".jpg", "").Split('x')[0]);

            int height = Convert.ToInt32(imgUrl.Split('!')[1].Replace(".jpg", "").Split('x')[1]);

            //图片已经存在直接输出

            if (File.Exists(context.Server.MapPath("~/" + imgUrl)))

            {

                OutPutImg("~/"+imgUrl);

            }

            else

            {

                if (!string.IsNullOrEmpty(imgUrl) && File.Exists(context.Server.MapPath("~/" + trueFilePath)))

                {

                    Image originalImage = System.Drawing.Image.FromFile(context.Server.MapPath("~/" + trueFilePath));

                    var newBitmap = new Bitmap(originalImage);

                    //生成相应的小图并保存

                    SendSmallImage(context.Server.MapPath("~/" + trueFilePath),context.Server.MapPath("~/" + imgUrl), width, height, "meiyouyisi");

                    //输出

                    OutPutImg("~/" + imgUrl);

                }

                else//图片如果不存在 输出默认图片

                {

                    //OutPutImg(imgUrl);

                }

            }

        }