asp.net生成缩略图示例方法分享


            做站的时候经常会遇到要生成缩略图的功能，因为可能不同的情况需要用来不同大小的缩略图。

本文生成的图片都为正方形，只有正方形的缩略图才是保证图片足够清晰。

当我我这里说的正方形是先按比例压缩，然后加一个固定的白底 然后居中显示。

代码：

新建outputimg.ashx

复制代码 代码如下://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));        }

复制代码 代码如下://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:

复制代码 代码如下://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);            }        }

复制代码 代码如下://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);                }            }        }