Problems generating a Lyapunov fractal

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VB

Following this link (with a working code in a Wolfram language):
http://demonstrations.wolfram.com/LyapunovFractals/[^]

generating the image should be pretty straight forward:
Choose a string of As and Bs of any nontrivial length (e.g., AABAB).
Construct the sequence S formed by successive terms in the string, repeated as many times as necessary.
Choose a point (a,b) \in [0,4] \times [0,4].
Define the function
r_n = a if S_n = A,
and
r_n = b if S_n = B.

Let x_0 = 0.5, and compute the iterates
x_{n+1} = r_n x_n (1 - x_n).

Compute the Lyapunov exponent:
\lambda = \lim_{N \rightarrow \infty} {1 \over N} \sum_{n = 1}^N \log \left|{dx_{n+1} \over dx_n}\right| = \lim_{N \rightarrow \infty} {1 \over N} \sum_{n = 1}^N \log |r_n (1 - 2x_n)|

In practice, \lambda is approximated by choosing a suitably large N.
Color the point (a,b) according to the value of \lambda obtained.
Repeat steps (3–7) for each point in the image plane.

' https://en.wikipedia.org/wiki/Lyapunov_fractal
  ' http://hypertextbook.com/chaos/44.shtml

  LyapunovCanvas.Background = Nothing

  ' Save the generating string (AB) into a char array
  Dim Sn As Char() = txtLyapunovGeneratingString.Text.ToString.ToCharArray

  ' Set the resolution of the image
  Dim LyapunovImageDimensions As Integer = 400

  'Calculate the scaling factor to get the appropriate a and b values
  Dim LyapunovScaleFactor = 4 / LyapunovImageDimensions

  Dim LyapunovLambdaArray(LyapunovImageDimensions + 1, LyapunovImageDimensions + 1) As Double

  Dim MAxValue, MinValue As Double
  MAxValue = Double.MinValue
  MinValue = Double.MaxValue

  ' The number of iterations to calculate the Lyapunov Exponent Lambda
  Dim N As Integer = 180

  ' The values a and b that should be between 0 and 4 unless you have zoomed in
  Dim a, b As Double

  For x As Integer = 0 To LyapunovImageDimensions
      For y As Integer = 0 To LyapunovImageDimensions

          ' Caluclate the a and b values from the placement
          a = LyapunovScaleFactor * x
          b = LyapunovScaleFactor * y

          ' Initialize the calcualtion parameters
          Dim rn As Double = 0
          Dim X0 As Double = 0.5
          Dim Xn As Double = X0
          Dim LyapunovExponent As Double = 0

          'Loop through the items in the generation string
          For CharItem As Integer = 0 To Sn.Length - 1

              ' Choose the value for rn based on the current item in the generating string
              rn = If(Sn(CharItem).ToString.ToUpper = "A", a, b)

              ' Reset the Xn value
              Xn = 0.5

              ' The iteration loop
              For NCount As Integer = 1 To N

                  ' Calcualte the exponent value and add a small value inside the logarithm
                  ' in case the clculated value is 0
                  LyapunovExponent += Math.Log(0.00001 + Math.Abs(rn * (1 - 2 * Xn))) / N

                  ' Create the next value of Xn
                  Xn = rn * Xn * (1 - Xn)
              Next
          Next

          ' Save the exponent value to the Image array
          LyapunovLambdaArray(x, y) = LyapunovExponent

          'Calculate the max and min values calculated (can be used for drawing the image)
          If MAxValue < LyapunovExponent Then
              MAxValue = LyapunovExponent
          End If

          If MinValue > LyapunovExponent Then
              MinValue = LyapunovExponent
          End If

      Next
  Next

  ' Create a Byte array of the image
  Dim buffer As New List(Of Byte)

  For x As Integer = 0 To LyapunovImageDimensions
      For y As Integer = 0 To LyapunovImageDimensions
          Dim k As Integer = 0

          Dim TempBrush As New SolidColorBrush

          ' Based on the value of the exponent
          If LyapunovLambdaArray(x, y) > 0.1 Then
              TempBrush = Brushes.Blue
          ElseIf LyapunovLambdaArray(x, y) < 0.1 Then
              TempBrush = Brushes.Yellow
          Else
              TempBrush = Brushes.Black
          End If

          buffer.Add(TempBrush.Color.B)
          buffer.Add(TempBrush.Color.G)
          buffer.Add(TempBrush.Color.R)
          buffer.Add(TempBrush.Color.A)

      Next
  Next

  Dim dpiX As Double = 96D
  Dim dpiY As Double = 96D
  Dim pixelFormat = PixelFormats.Pbgra32
  Dim bytesPerPixel = Math.Truncate(((pixelFormat.BitsPerPixel + 7) / 8))
  Dim stride = bytesPerPixel * (LyapunovImageDimensions + 1)


  Dim img As New ImageBrush
  img.ImageSource = BitmapSource.Create(LyapunovImageDimensions, LyapunovImageDimensions, dpiX, dpiY,
                                   pixelFormat, Nothing, buffer.ToArray, stride) '
  LyapunovCanvas.Background = img

But the images that are created looks nothing like they should. Can anyone spot my mistake here?