asp.net生成缩略图示例方法分享

发布时间：2023-02-27 22:39:25 来源：好代码

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工作是一种乐趣时，生活是一种享受！工作是一种义务时，生活则是一种苦役。对待平凡的工作要用不平凡的态度去面对。

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


//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:


//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);
 }
 }
 }