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(); 
  } 
}