Imports System.Drawing.Imaging
Imports System.Runtime.InteropServices.Marshal

Function ColorToGrey(ByVal bm As Bitmap) As Bitmap
        Dim bd As BitmapData = bm.LockBits(New Rectangle(0, 0, bm.Width, _
          bm.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb)
        Dim bz As Int32 = (bd.Stride * bm.Height)                               _
          ' Byte pro Zeile = Stride*Höhe
        Dim b(bz - 1) As Byte                                                   _
          ' das ByteArray
        Copy(bd.Scan0, b, 0, bz)                                                _
         ' Werte ins Array kopieren                                                         
        Dim gray As Byte                                                        _
          ' Scan0  = Anfang Zeile 0 
        For i As Int32 = 0 To bz - 3 Step 3                                     _
              ' 3 Byte pro Pixel
            gray = CByte(b(i) * 0.11 + b(i + 1) * 0.59 + b(i + 2) * 0.3)
            b(i) = gray
            b(i + 1) = gray
            b(i + 2) = gray
        Next
        Copy(b, 0, bd.Scan0, bz)                                                _
            ' Array zurückschreiben
        bm.UnlockBits(bd)
        Return bm
End Function