asp.net生成指定大小缩略图

asp.net生成指定大小缩略图，如果图片小于 指定大小，则显示在指定大小画布的中间，如果图片大于 指定大小，则先对图片等比例缩放，在写到指定大小的画板上。可以直接输出到页面，也可以保存为文件。关键代码如下：有哪些可以改进的地方 还请大家提出来，谢谢。

直接复制下来 就可以用：注意引用这三个namespace：

using System.Drawing; using System.Drawing.Drawing2D; using System.IO; using System; public class A { /// <summary> /// 根据路径读取文件，支持远程文件，本地文件 ///</summary> ///<param name="path"></param> /// <returns></returns> private System.Drawing.Image GetImage(string path) { if (path.StartsWith("http")) { System.Net.WebRequest request = System.Net.WebRequest.Create(path); request.Timeout = 10000; System.Net.HttpWebResponse httpresponse = (System.Net.HttpWebResponse)request.GetResponse(); Stream s = httpresponse.GetResponseStream(); return System.Drawing.Image.FromStream(s); } else { return System.Drawing.Image.FromFile(path); } } /// <summary>创建规定大小的图像</summary> /// <param name="oPath">源图像绝对路径</param> /// <param name="tPath">生成图像绝对路径</param> /// <param name="width">生成图像的宽度</param> /// <param name="height">生成图像的高度</param> public void CreateImageOutput(int width, int height, string oPath) { Bitmap originalBmp = null;// new Bitmap(oPath); originalBmp = new Bitmap(GetImage(oPath)); // 源图像在新图像中的位置 int left, top; if (originalBmp.Width <= width && originalBmp.Height <= height) { // 原图像的宽度和高度都小于生成的图片大小 left = (int)Math.Round((decimal)(width - originalBmp.Width) / 2); top = (int)Math.Round((decimal)(height - originalBmp.Height) / 2); // 最终生成的图像 Bitmap bmpOut = new Bitmap(width, height); using (Graphics graphics = Graphics.FromImage(bmpOut)) { // 设置高质量插值法 graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; // 清空画布并以白色背景色填充 graphics.Clear(Color.White); //加上边框 //Pen pen = new Pen(ColorTranslator.FromHtml("#cccccc")); // graphics.DrawRectangle(pen, 0, 0, width - 1, height - 1); // 把源图画到新的画布上 graphics.DrawImage(originalBmp, left, top); } // bmpOut.Save(tPath); //保存为文件，tpath 为要保存的路径 this.OutputImgToPage(bmpOut);//直接输出到页面 bmpOut.Dispose(); return; } // 新图片的宽度和高度，如400*200的图像，想要生成160*120的图且不变形， // 那么生成的图像应该是160*80，然后再把160*80的图像画到160*120的画布上 int newWidth, newHeight; if (width * originalBmp.Height < height * originalBmp.Width) { newWidth = width; newHeight = (int)Math.Round((decimal)originalBmp.Height * width / originalBmp.Width); // 缩放成宽度跟预定义的宽度相同的，即left=0，计算top left = 0; top = (int)Math.Round((decimal)(height - newHeight) / 2); } else { newWidth = (int)Math.Round((decimal)originalBmp.Width * height / originalBmp.Height); newHeight = height; // 缩放成高度跟预定义的高度相同的，即top=0，计算left left = (int)Math.Round((decimal)(width - newWidth) / 2); top = 0; } // 生成按比例缩放的图，如：160*80的图 Bitmap bmpOut2 = new Bitmap(newWidth, newHeight); using (Graphics graphics = Graphics.FromImage(bmpOut2)) { graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; graphics.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight); graphics.DrawImage(originalBmp, 0, 0, newWidth, newHeight); } // 再把该图画到预先定义的宽高的画布上，如160*120 Bitmap lastbmp = new Bitmap(width, height); using (Graphics graphics = Graphics.FromImage(lastbmp)) { // 设置高质量插值法 graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; // 清空画布并以白色背景色填充 graphics.Clear(Color.White); //加上边框 //Pen pen = new Pen(ColorTranslator.FromHtml("#cccccc")); //graphics.DrawRectangle(pen, 0, 0, width - 1, height - 1); // 把源图画到新的画布上 graphics.DrawImage(bmpOut2, left, top); } // lastbmp.Save(tPath);//保存为文件，tpath 为要保存的路径 this.OutputImgToPage(lastbmp); //直接输出到页面 lastbmp.Dispose(); } private void OutputImgToPage(System.Drawing.Bitmap bmp) { //输出到页面 MemoryStream ms = new MemoryStream(); bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); Response.ClearContent(); //需要输出图象信息 要修改HTTP头 byte[] buffer = ms.ToArray(); Response.AddHeader("Content-type", "image/jpeg"); Response.BinaryWrite(buffer); bmp.Dispose(); } }

using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;

/// <summary>  

 /// 根据路径读取文件，支持远程文件，本地文件  

   /// </summary>
   /// <param name="path"></param>
   /// <returns></returns>
   private System.Drawing.Image GetImage(string path)
   {
       if (path.StartsWith("http"))
       {
           System.Net.WebRequest request = System.Net.WebRequest.Create(path);
           request.Timeout = 10000;
           System.Net.HttpWebResponse httpresponse = (System.Net.HttpWebResponse)request.GetResponse();
           Stream s = httpresponse.GetResponseStream();

           return System.Drawing.Image.FromStream(s);
       }
       else
       {
           return System.Drawing.Image.FromFile(path);
       }
   }

   /// <summary>创建规定大小的图像
   /// </summary>
   /// <param name="oPath">源图像绝对路径</param>
   /// <param name="tPath">生成图像绝对路径</param>
   /// <param name="width">生成图像的宽度</param>
   /// <param name="height">生成图像的高度</param>
   public void CreateImageOutput(int width, int height, string oPath)
   {
       Bitmap originalBmp = null;// new Bitmap(oPath);
       originalBmp = new Bitmap(GetImage(oPath));
       // 源图像在新图像中的位置
       int left, top;


       if (originalBmp.Width <= width && originalBmp.Height <= height)
       {
           // 原图像的宽度和高度都小于生成的图片大小
           left = (int)Math.Round((decimal)(width - originalBmp.Width) / 2);
           top = (int)Math.Round((decimal)(height - originalBmp.Height) / 2);


           // 最终生成的图像
           Bitmap bmpOut = new Bitmap(width, height);
           using (Graphics graphics = Graphics.FromImage(bmpOut))
           {
               // 设置高质量插值法
               graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
               // 清空画布并以白色背景色填充
               graphics.Clear(Color.White);
               //加上边框
               //Pen pen = new Pen(ColorTranslator.FromHtml("#cccccc"));
               // graphics.DrawRectangle(pen, 0, 0, width - 1, height - 1);
               // 把源图画到新的画布上
               graphics.DrawImage(originalBmp, left, top);
           }
           // bmpOut.Save(tPath);//保存为文件，tpath 为要保存的路径
           this.OutputImgToPage(bmpOut);//直接输出到页面
           bmpOut.Dispose();
           return;
       }


       // 新图片的宽度和高度，如400*200的图像，想要生成160*120的图且不变形，
       // 那么生成的图像应该是160*80，然后再把160*80的图像画到160*120的画布上
       int newWidth, newHeight;
       if (width * originalBmp.Height < height * originalBmp.Width)
       {
           newWidth = width;
           newHeight = (int)Math.Round((decimal)originalBmp.Height * width / originalBmp.Width);
           // 缩放成宽度跟预定义的宽度相同的，即left=0，计算top
           left = 0;
           top = (int)Math.Round((decimal)(height - newHeight) / 2);
       }
       else
       {
           newWidth = (int)Math.Round((decimal)originalBmp.Width * height / originalBmp.Height);
           newHeight = height;
           // 缩放成高度跟预定义的高度相同的，即top=0，计算left
           left = (int)Math.Round((decimal)(width - newWidth) / 2);
           top = 0;
       }


       // 生成按比例缩放的图，如：160*80的图
       Bitmap bmpOut2 = new Bitmap(newWidth, newHeight);
       using (Graphics graphics = Graphics.FromImage(bmpOut2))
       {
           graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
           graphics.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight);
           graphics.DrawImage(originalBmp, 0, 0, newWidth, newHeight);
       }
       // 再把该图画到预先定义的宽高的画布上，如160*120
       Bitmap lastbmp = new Bitmap(width, height);
       using (Graphics graphics = Graphics.FromImage(lastbmp))
       {
           // 设置高质量插值法
           graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
           // 清空画布并以白色背景色填充
           graphics.Clear(Color.White);
           //加上边框
           //Pen pen = new Pen(ColorTranslator.FromHtml("#cccccc"));
           //graphics.DrawRectangle(pen, 0, 0, width - 1, height - 1);
           // 把源图画到新的画布上
           graphics.DrawImage(bmpOut2, left, top);
       }
       // lastbmp.Save(tPath);//保存为文件，tpath 为要保存的路径
       this.OutputImgToPage(lastbmp);//直接输出到页面
       lastbmp.Dispose();
   }


   private void OutputImgToPage(System.Drawing.Bitmap bmp)
   {
       //输出到页面
       MemoryStream ms = new MemoryStream();
       bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);

       Response.ClearContent(); //需要输出图象信息 要修改HTTP头
       byte[] buffer = ms.ToArray();

       Response.AddHeader("Content-type", "image/jpeg");
       Response.BinaryWrite(buffer);
       bmp.Dispose();
   }