A similar problem exists in structured illumination microscopy that uses a linear grid. the following references might help: http://dx.doi.org/10.1046/j.1365-2818.2001.00894.x <http://dx.doi.org/10.1046/j.1365-2818.2001.00894.x> http://dx.doi.org/10.1111/j.0022-2720.2004.01411.x <http://dx.doi.org/10.1111/j.0022-2720.2004.01411.x> -- arwed weigel abteilung fuer neurophysiology und zellulaere biophysik universitaet goettingen humboldtallee 23 37073 goettingen phon +49 (0)551 395918 fax +49 (0)551 398399