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();  
    }  
}