C#无损高质量压缩图片代码

/// 无损压缩图片  
/// <param name="sfile">原图片</param>  
/// <param name="dfile">压缩后保存位置</param>  
/// <param name="dheight">高度</param>  
/// <param name="dwidth"></param>  
/// <param name="flag">压缩质量(数字越小压缩率越高) 1-100</param>  
/// <returns></returns>  
 
public static bool getpicthumbnail(string sfile, string dfile, int dheight, int dwidth, int flag) 
{ 
  system.drawing.image isource = system.drawing.image.fromfile(sfile); 
  imageformat tformat = isource.rawformat; 
  int sw = 0, sh = 0; 
 
  //按比例缩放 
  size tem_size = new size(isource.width, isource.height); 
 
  if (tem_size.width > dheight || tem_size.width > dwidth) 
  { 
    if ((tem_size.width * dheight) > (tem_size.width * dwidth)) 
    { 
      sw = dwidth; 
      sh = (dwidth * tem_size.height) / tem_size.width; 
    } 
    else 
    { 
      sh = dheight; 
      sw = (tem_size.width * dheight) / tem_size.height; 
    } 
  } 
  else 
  { 
    sw = tem_size.width; 
    sh = tem_size.height; 
  } 
 
  bitmap ob = new bitmap(dwidth, dheight); 
  graphics g = graphics.fromimage(ob); 
 
  g.clear(color.whitesmoke); 
  g.compositingquality = compositingquality.highquality; 
  g.smoothingmode = smoothingmode.highquality; 
  g.interpolationmode = interpolationmode.highqualitybicubic; 
 
  g.drawimage(isource, new rectangle((dwidth - sw) / 2, (dheight - sh) / 2, sw, sh), 0, 0, isource.width, isource.height, graphicsunit.pixel); 
 
  g.dispose(); 
  //以下代码为保存图片时，设置压缩质量  
  encoderparameters ep = new encoderparameters(); 
  long[] qy = new long[1]; 
  qy[0] = flag;//设置压缩的比例1-100  
  encoderparameter eparam = new encoderparameter(system.drawing.imaging.encoder.quality, qy); 
  ep.param[0] = eparam; 
  try 
  { 
    imagecodecinfo[] arrayici = imagecodecinfo.getimageencoders(); 
    imagecodecinfo jpegiciinfo = null; 
    for (int x = 0; x < arrayici.length; x++) 
    { 
      if (arrayici[x].formatdescription.equals("jpeg")) 
      { 
        jpegiciinfo = arrayici[x]; 
        break; 
      } 
    } 
    if (jpegiciinfo != null) 
    { 
      ob.save(dfile, jpegiciinfo, ep);//dfile是压缩后的新路径  
    } 
    else 
    { 
      ob.save(dfile, tformat); 
    } 
    return true; 
  } 
  catch 
  { 
    return false; 
  } 
  finally 
  { 
    isource.dispose(); 
    ob.dispose(); 
  } 
}