Blur with LockBits not working?

[minitech]

Oh, and I also did a test like this:

Public Class Form1
    Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
        Dim g As Graphics = e.Graphics
        Dim img As Bitmap = My.Resources.test.Clone()
        LockBitsTest(img)
        g.DrawImage(img, 10, 10)
        MyBase.OnPaint(e)
    End Sub
    Private Sub LockBitsTest(ByVal img As Bitmap)
        Dim b_data As Drawing.Imaging.BitmapData = img.LockBits(New Rectangle(0, 0, img.Width, img.Height), Imaging.ImageLockMode.ReadWrite, Imaging.PixelFormat.Format32bppArgb)
        Dim ptr As IntPtr = b_data.Scan0
        Dim bytes As Integer = b_data.Stride * b_data.Height
        Dim img_bytes(bytes - 1) As Byte
        System.Runtime.InteropServices.Marshal.Copy(ptr, img_bytes, 0, bytes)
        Dim y, x As Integer
        For y = 1 To img.Height - 2
            For x = 1 To img.Width - 2
                Try
                    img_bytes((y * img.Width + x) * 4) = 255
                    img_bytes((y * img.Width + x) * 4 + 1) = 255
                    'img_bytes((y * img.Width + x) * 4 + 2) = n_px.G
                    'img_bytes((y * img.Width + x) * 4 + 3) = n_px.B
                Catch ex As Exception
                    GoTo finish_sub
                End Try
            Next
        Next
finish_sub:
        img.UnlockBits(b_data)
    End Sub
End Class

It gave me no errors, but the image didn't change.

What's wrong?