  Spatial light modulators can typically only modulate the phase or the
amplitude of an incident wavefront, with only a limited number of discrete
values available. This is often accounted for in computer-generated holography
algorithms by setting hologram pixel values to the nearest achievable value
during what is known as quantisation. Sympathetic quantisation is an
alternative to this nearest-neighbour approach that takes into account the
underlying diffraction relationships in order to obtain a significantly
improved post-quantisation performance. The concept of sympathetic quantisation
is introduced in this paper and a simple implementation, soft sympathetic
quantisation, is presented which is shown to improve mean squared error and
structural similarity index error metrics by 50% for the considered case of
single-transform algorithms.
