C# 无损压缩图片

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  1         /// <summary>
  2         /// 降低图片质量
  3         /// </summary>
  4         /// <param name="sFile">文件流</param>
  5         /// <param name="flag">压缩倍率（1-100）</param>
  6         /// <param name="size">输出最大流尺寸（单位：MB）</param>
  7         /// <param name="sfsc">是否第一次执行方法</param>
  8         /// <returns></returns>
  9         privatestaticStream ReducePictureQuality(Stream sFile, int flag =90, int size =1, bool sfsc =true)
 10         {
 11 
 12             MemoryStream outStream =newMemoryStream();
 13 
 14             //如果是第一次调用，原始图像的大小小于要压缩的大小，则直接复制文件，并且返回true
 15 
 16             //FileInfo firstFileInfo = new FileInfo(sFile);
 17 
 18             if (sfsc ==true&& sFile.Length < size *1024*1024)
 19             {
 20                 return sFile;
 21             }
 22 
 23             Image iSource =Image.FromStream(sFile);
 24             ImageFormat tFormat = iSource.RawFormat;
 25             int dHeight = iSource.Height /2;
 26             int dWidth = iSource.Width /2;
 27 
 28             int sW =0, sH =0;
 29             //按比例缩放
 30             Size tem_size =newSize(iSource.Width, iSource.Height);
 31             if (tem_size.Width > dHeight || tem_size.Width > dWidth)
 32             {
 33                 if ((tem_size.Width * dHeight) > (tem_size.Width * dWidth))
 34                 {
 35                     sW = dWidth;
 36                     sH = (dWidth * tem_size.Height) / tem_size.Width;
 37                 }
 38                 else
 39                 {
 40                     sH = dHeight;
 41                     sW = (tem_size.Width * dHeight) / tem_size.Height;
 42                 }
 43             }
 44             else
 45             {
 46                 sW = tem_size.Width;
 47                 sH = tem_size.Height;
 48            }
 49             Bitmap ob =newBitmap(dWidth, dHeight);
 50             Graphics g =Graphics.FromImage(ob);
 51             g.Clear(Color.WhiteSmoke);
 52 
 53             g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
 54 
 55             g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
 56 
 57             g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
 58 
 59             g.DrawImage(iSource, newRectangle((dWidth - sW) /2, (dHeight - sH) /2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);
 60 
 61             g.Dispose();
 62 
 63             //以下代码为保存图片时，设置压缩质量
 64 
 65             EncoderParameters ep =newEncoderParameters();
 66 
 67             long[] qy =newlong[1];
 68 
 69             qy[0] = flag;//设置压缩的比例1-100
 70 
 71             EncoderParameter eParam =newEncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
 72 
 73             ep.Param[0] = eParam;
 74 
 75             try
 76             {
 77                 ImageCodecInfo[] arrayICI =ImageCodecInfo.GetImageEncoders();
 78 
 79                 ImageCodecInfo jpegICIinfo =null;
 80 
 81                 for (int x =0; x < arrayICI.Length; x++)
 82                 {
 83                     if (arrayICI[x].FormatDescription.Equals("JPEG"))
 84                     {
 85                         jpegICIinfo = arrayICI[x];
 86                         break;
 87                     }
 88                 }
 89 
 90                 if (jpegICIinfo !=null)
 91                 {
 92                     ob.Save(outStream, jpegICIinfo, ep);//dFile是压缩后的新路径////
 93                     //FileInfo fi = new FileInfo();
 94                     if (outStream.Length >1024*1024* size)
 95                     {
 96                         flag = flag -10;
 97 
 98                         ReducePictureQuality(outStream, flag, size, false);
 99 
100                     }
101 
102                 }
103 
104                 else
105                 {
106 
107                     ob.Save(outStream, tFormat);
108 
109                 }
110 
111                 return outStream;
112 
113             }
114 
115             catch (Exception ex)
116             {
117                 returnnull;
118             }
119 
120             finally
121             {
122                 iSource.Dispose();
123                 ob.Dispose();
124 
125             }
126         }
127

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