This version adds the following GetPixel and SetPixel methods to the class. These methods calculate a pixel's location in the array and then gets or sets the pixel's red, green, and blue byte values.

' Return a pixel's byte values.
Public Sub GetPixel(ByVal x As Integer, ByVal y As Integer, _
    ByRef r As Byte, ByRef g As Byte, ByRef b As Byte)
    Dim offset As Integer = y * RowSizeBytes + x * _
        PixelSizeBytes
    b = ImageBytes(offset)
    g = ImageBytes(offset + 1)
    r = ImageBytes(offset + 2)
End Sub

' Set a pixel's byte values.
Public Sub SetPixel(ByVal x As Integer, ByVal y As Integer, _
    ByVal r As Byte, ByVal g As Byte, ByVal b As Byte)
    Dim offset As Integer = y * RowSizeBytes + x * _
        PixelSizeBytes
    ImageBytes(offset) = b
    ImageBytes(offset + 1) = g
    ImageBytes(offset + 2) = r
End Sub

Private m_Filter(,) As Integer
Private m_Weight As Integer

' Initialize the filter.
Private Sub Form1_Load(ByVal sender As System.Object, ByVal _
    e As System.EventArgs) Handles MyBase.Load
    m_Filter = New Integer(,) { _
        {-1, 0, 0}, _
        {0, 0, 0}, _
        {0, 0, 1}}
    m_Weight = 1
End Sub

For an embossing filter, the program then adds 127 to make pixels with a neutral value become gray.

' Apply the filter to the image.
Private Sub ApplyFilter()
    Me.Cursor = Cursors.WaitCursor
    picNew.Image = Nothing
    Me.Refresh()
    Dim start_time As Date = Now

    Dim bm1 As Bitmap = picOld.Image
    Dim bm2 As New Bitmap(bm1.Width, bm1.Height)

    ' Make BitmapBytesRGB24 objects for the bitmaps.
    Dim bm1_bytes As New BitmapBytesRGB24(bm1)
    Dim bm2_bytes As New BitmapBytesRGB24(bm2)

    ' Lock the bitmaps' bytes.
    bm1_bytes.LockBitmap()
    bm2_bytes.LockBitmap()

    Dim wid As Integer = bm1.Width
    Dim hgt As Integer = bm1.Height
    Dim new_r As Byte = 0
    Dim new_g As Byte = 0
    Dim new_b As Byte = 0
    For x As Integer = 1 To wid - 2
        For y As Integer = 1 To hgt - 2
            Dim r As Integer = 0
            Dim g As Integer = 0
            Dim b As Integer = 0
            For dx As Integer = 0 To 2
                For dy As Integer = 0 To 2
                    bm1_bytes.GetPixel(x + dx - 1, y + dy - _
                        1, new_r, new_g, new_b)
                    r += new_r * m_Filter(dx, dy)
                    g += new_g * m_Filter(dx, dy)
                    b += new_b * m_Filter(dx, dy)
                Next dy
            Next dx

            r = CInt(127 + r / m_Weight)
            g = CInt(127 + g / m_Weight)
            b = CInt(127 + b / m_Weight)
            If r < 0 Then r = 0
            If g < 0 Then g = 0
            If b < 0 Then b = 0
            If r > 255 Then r = 255
            If g > 255 Then g = 255
            If b > 255 Then b = 255
            bm2_bytes.SetPixel(x, y, r, g, b)
        Next y
    Next x

    ' Unlock the bitmaps.
    bm1_bytes.UnlockBitmap()
    bm2_bytes.UnlockBitmap()

    Dim stop_time As Date = Now
    Dim elapsed_time As TimeSpan = stop_time - start_time
    Debug.WriteLine(elapsed_time.TotalSeconds.ToString("0.00") _
        & " seconds")
    picNew.Image = bm2
    picNew.Refresh()
    Me.Cursor = Cursors.Default
End Sub