HOWTO: Apply Photoshop-like Threshold

    Public Sub ApplyThreshold(ByRef bitmap As Aurigma.GraphicsMill.Bitmap, ByVal threshold As Integer)

        ' Get and lock the raw data for the bitmap
        Dim data As Aurigma.GraphicsMill.BitmapData = bitmap.LockBits()

        ' How many bytes one pixel occupies
        Dim pixelSize As Integer = data.BitsPerPixel / 8

        ' Number of bytes in a row
        Dim stride As Integer = data.Stride

        ' Number of rows
        Dim height As Integer = data.Height

        ' Pointer to the beginning of the pixel data region
        Dim pointer As IntPtr = data.Scan0

        ' Array to represent a single pixel
        Dim pixel(pixelSize - 1) As Byte

        Dim i, j As Integer
        For i = 0 To height - 1
            j = 0
            Do While j < stride
                ' Read a single pixel
                Marshal.Copy(pointer, pixel, 0, pixelSize)
                ' Now modify the pixel, in this case clamp to 0 or max based on the threshold value
                If pixel(0) > threshold Then
                    pixel(0) = 255
                Else
                    pixel(0) = 0
                End If

                ' Write back the pixel data
                Marshal.Copy(pixel, 0, pointer, pixelSize)

                ' Compute the memory location of the next pixel
                pointer = IntPtr.op_Explicit(pointer.ToInt32 + pixelSize)
                j = j + pixelSize
            Loop
        Next i

        bitmap.UnlockBits(data)

    End Sub