c#无损高质量压缩图片

这几天在做同城交友网www.niyuewo.com时遇到的一个问题，如何将会员的头像压缩，在网上搜索整理如下：在此也感谢医药精(www.yiyaojing.com)站长的帮忙

 /// <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"></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) //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;
                    }
                }
                iSource.Dispose();
                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
            {               
                ob.Dispose();
            }

        }