A method of producing a phase-only computer generated hologram for a pixellated Spatial Light Modulator device (200) supporting a discrete number of modulation levels and having an integrated layer of liquid crystal material above a silicon circuit, the method comprising: determining punctuated replay coordinates in a Fourier transform plane (202) of the SLM (200); using said coordinates for calculating the size in pixels of a base cell;
evaluating a holographic base cell pattern using a phase quantisation procedure and replicating said base cell in the plane of the said hologram device 200) until the entire aperture of the hologram device is filled.