How would I apply smoothing to a noise map

i am making a perlin noise generator on a WFP and i have generated the noise map but would im not sure how to apply smoothing to said map, here is what i have so far

private void btnGenerate_Click(object sender, EventArgs e)
       {
           CellHeight = 8;
           CellWidth = 8;
           MapWidth = 80;
           MapHeight = 80;
           double[,] noise_map = new double[MapWidth, MapHeight];
           TranslateNoise(InitWhiteNoise(noise_map));
       }

       private void TranslateNoise(double[,] noise_map)
       {
           Bitmap noiseMap = new Bitmap(MapWidth * CellWidth, MapHeight * CellHeight);
           using (Graphics pMap = Graphics.FromImage(noiseMap))
           {
               <pre>                pMap.Clear(Color.Black);
               for (int y = 0; y < MapHeight; y++)
               {
                   for (int x = 0; x < MapWidth; x++)
                   {
                       pMap.FillRectangle(
                           noise_map[x, y] == 0 ? Brushes.White :
                           noise_map[x, y] == 1 ? Brushes.WhiteSmoke :
                           noise_map[x, y] == 2 ? Brushes.Gainsboro :
                           noise_map[x, y] == 3 ? Brushes.LightGray :
                           noise_map[x, y] == 4 ? Brushes.Silver :
                           noise_map[x, y] == 5 ? Brushes.Gray :
                           noise_map[x, y] == 6 ? Brushes.DarkGray :
                           noise_map[x, y] == 7 ? Brushes.LightSlateGray :
                           noise_map[x, y] == 8 ? Brushes.SlateGray :
                           noise_map[x, y] == 9 ? Brushes.DimGray : Brushes.Black, x * CellWidth, y * CellHeight,
                           CellWidth, CellHeight);
                   }
               }
           }

           pbMap.Image = noiseMap;
       }
       private double[,] InitWhiteNoise(double[,] noise_map)
       {
           Random noise = new Random();
           for (int x = 0; x < MapWidth; x++)
               for (int y = 0; y < MapHeight; y++)
                   noise_map[x, y] = noise.Nex(0, 11);

           return noise_map;
       }