C# 图片无损压缩

         /// <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 static bool CompressImage(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.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();  
             }  
   
         }