How do I improve my dither to 16 bit color 565 and reduce colors(16 colors)

public BitmapImage BitMapSourceToBitmapImage(BitmapSource bitmapSource)
        {
            PngBitmapEncoder encoder = new PngBitmapEncoder();
            MemoryStream memoryStream = new MemoryStream();
            BitmapImage bImg = new BitmapImage();

            encoder.Frames.Add(BitmapFrame.Create(bitmapSource));
            encoder.Save(memoryStream);

            memoryStream.Position = 0;
            bImg.BeginInit();
            bImg.StreamSource = memoryStream;
            bImg.EndInit();
            return bImg;
        }

private System.Drawing.Bitmap BitmapImage2Bitmap(BitmapImage bitmapImage)
        {
            using (MemoryStream outStream = new MemoryStream())
            {
                BmpBitmapEncoder enc = new BmpBitmapEncoder();
                enc.Frames.Add(BitmapFrame.Create(bitmapImage));
                enc.Save(outStream);
                    System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(outStream);

                return new System.Drawing.Bitmap(bitmap);
            }
        }

public static Bitmap ConvertTo16bpp(Bitmap img)
        {
            var bmp = new Bitmap(img.Width, img.Height,
                          System.Drawing.Imaging.PixelFormat.Format16bppRgb565);
            using (var gr = Graphics.FromImage(bmp))
                gr.DrawImage(img, new Rectangle(0, 0, img.Width, img.Height));
            return bmp;
        }

private BitmapSource BitReduction(BitmapImage myBitmapImageFit)
        {
            FormatConvertedBitmap fcb = new FormatConvertedBitmap();
            fcb.BeginInit();
            fcb.Source = myBitmapImageFit as BitmapSource;
            fcb.DestinationFormat = System.Windows.Media.PixelFormats.Indexed4;
            fcb.DestinationPalette = BitmapPalettes.Halftone8;
            fcb.EndInit();
            return (fcb as BitmapSource);
        }

private void ApplyFilter(string path)
        {
            BitmapImage myBitmapImage = new BitmapImage();
            // BitmapSource objects like BitmapImage can only have their properties
            // changed within a BeginInit/EndInit block.
            myBitmapImage.BeginInit();
            myBitmapImage.UriSource = new Uri(path);
            myBitmapImage.DecodePixelHeight = 240;
            myBitmapImage.DecodePixelWidth = 320;
            myBitmapImage.EndInit();

            var imageProcessed = ConvertTo16bpp(BitmapImage2Bitmap(myBitmapImage));
            var newbitmapimage = BitmapToBistmapImage(imageProcessed);
            BitmapSource bitmapSource = BitReduction(newbitmapimage);
            var bitmapToProcess = 
             BitmapImage2Bitmap(BitMapSourceToBitmapImage(bitmapSource));
            
            bitmapToProcess.Save(@"C:\image6.bmp");

byte[] byteArray = new byte[350000];

byteArray = File.ReadAllBytes(@"C:\image6.bmp");

List<string> result = new List<string> 
             (System.Text.RegularExpressions.Regex.Split(hello2, @"(?<=\G.{2})", 
              System.Text.RegularExpressions.RegexOptions.Singleline));
              string newstring = string.Join(" ", result);