.net 图片无损压缩

 using System.Drawing.Imaging; 
 using System.Drawing; 
 using System.Drawing.Drawing2D;

#region GetPicThumbnail
    /// <summary>
    /// 无损压缩图片
    /// </summary>
    /// <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">宽度</param>
    /// <param name="flag">压缩质量 1-100</param>
    /// <returns></returns>
 
    public 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) //将**改成c#中的或者操作符号
        {
            if ((tem_size.Width * dHeight) > (tem_size.Height * 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();
 
        }
    }
    #endregion