ASP.NET 生成高质量缩略图代码

   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 size(convert.toint32(w), convert.toint32(h));
  }

  public static void sendsmallimage(string filename, string newfile, int maxheight, int maxwidth)
  {
   system.drawing.image img = system.drawing.image.fromfile(filename);
   system.drawing.imaging.imageformat thisformat = img.rawformat;

   size newsize = newsize(maxwidth, maxheight, img.width, img.height);
   bitmap outbmp = new bitmap(newsize.width, newsize.height);
   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.drawimage(img, new rectangle(0, 0, 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;

   //获得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();
  }