' Convert each pixel to grayscale.
Private Sub btnGrayscale_Click(ByVal sender As _
    System.Object, ByVal e As System.EventArgs) Handles _
    btnGrayscale.Click
    Dim clr As Integer
    Dim xmax As Integer
    Dim ymax As Integer
    Dim x As Integer
    Dim y As Integer

    ' Get the bitmap and its dimensions.
    Dim bm As Bitmap = picImage.Image
    xmax = bm.Width - 1
    ymax = bm.Height - 1

    ' Convert the pixels to grayscale.
    For y = 0 To ymax
        For x = 0 To xmax
            ' Convert this pixel.
            With bm.GetPixel(x, y)
                clr = 0.3 * .R + 0.5 * .G + 0.2 * .B
            End With
            bm.SetPixel(x, y, _
                Color.FromArgb(255, clr, clr, clr))
        Next x
    Next y

    ' Display the results.
    picImage.Image = bm
End Sub