Blur with LockBits not working?

[minitech]

I tried using LockBits to blur images, since I heard it was faster, and there's no error, but there's no blur either. It doesn't do anything. The commented-out code is the code I had before using LockBits, and it works.

Private Sub BlurImage(ByVal img As Bitmap, Optional ByVal radius As Integer = 3, Optional ByVal blur_bounds As Object = Nothing)
        Dim bb As Rectangle
        If blur_bounds IsNot Nothing Then
            bb = CType(blur_bounds, Rectangle)
        Else
            bb = New Rectangle(0, 0, img.Width, img.Height)
        End If
        Dim b_data As Drawing.Imaging.BitmapData = img.LockBits(bb, 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 i As Integer
        For i = 0 To radius
            Dim y, x As Integer
            For y = (bb.Y + 1) To bb.Bottom - 1
                For x = (bb.X + 1) To bb.Right - 1
                    Try
                        'Dim px_up As Color = img.GetPixel(x, y - 1)
                        'Dim px_down As Color = img.GetPixel(x, y + 1)
                        'Dim px_left As Color = img.GetPixel(x - 1, y)
                        'Dim px_right As Color = img.GetPixel(x + 1, y)
                        'Dim pxR As Integer = Average_Int(px_up.R, px_down.R, px_left.R, px_right.R) ', 90)
                        'Dim pxG As Integer = Average_Int(px_up.G, px_down.G, px_left.G, px_right.G) ', 90)
                        'Dim pxB As Integer = Average_Int(px_up.B, px_down.B, px_left.B, px_right.B) ', 90) '90s are added for "blackness"
                        'Dim n_px As Color = Color.FromArgb(255, pxR, pxG, pxB)
                        'img.SetPixel(x, y, n_px)
                        Dim px_up As Color = Color.FromArgb(img_bytes(((y - 1) * bb.Width + x) * 4), img_bytes(((y - 1) * bb.Width + x) * 4 + 1), img_bytes(((y - 1) * bb.Width + x) * 4 + 2), img_bytes(((y - 1) * bb.Width + x) * 4 + 3))
                        Dim px_down As Color = Color.FromArgb(img_bytes(((y + 1) * bb.Width + x) * 4), img_bytes(((y + 1) * bb.Width + x) * 4 + 1), img_bytes(((y + 1) * bb.Width + x) * 4 + 2), img_bytes(((y + 1) * bb.Width + x) * 4 + 3))
                        Dim px_left As Color = Color.FromArgb(img_bytes((y * bb.Width + (x - 1)) * 4), img_bytes((y * bb.Width + (x - 1)) * 4 + 1), img_bytes((y * bb.Width + (x - 1)) * 4 + 2), img_bytes((y * bb.Width + (x - 1)) * 4 + 3))
                        Dim px_right As Color = Color.FromArgb(img_bytes((y * bb.Width + (x + 1)) * 4), img_bytes((y * bb.Width + (x + 1)) * 4 + 1), img_bytes((y * bb.Width + (x + 1)) * 4 + 2), img_bytes((y * bb.Width + (x + 1)) * 4 + 3))
                        Dim pxR As Integer = Average_Int(px_up.R, px_down.R, px_left.R, px_right.R)
                        Dim pxG As Integer = Average_Int(px_up.G, px_down.G, px_left.G, px_right.G)
                        Dim pxB As Integer = Average_Int(px_up.B, px_down.B, px_left.B, px_right.B)
                        Dim n_px As Color = Color.FromArgb(255, pxR, pxG, pxB)
                        img_bytes((y * bb.Width + x) * 4) = n_px.A
                        img_bytes((y * bb.Width + x) * 4 + 1) = n_px.R
                        img_bytes((y * bb.Width + x) * 4 + 2) = n_px.G
                        img_bytes((y * bb.Width + x) * 4 + 3) = n_px.B
                    Catch ex As Exception
                        GoTo finish_sub
                    End Try
                Next
            Next
        Next
finish_sub:
        img.UnlockBits(b_data)
    End Sub