Hologram Viewing Arrangement and Alignment Device

A method of indicating displacement using a pixellated phase mask and a pixellated hologram, said hologram storing data representing at least two images such that disposing the phase mask in a first position with respect to the display substrate enables one of the at least two images to be visible and disposing the phase mask in a second position with respect to the display substrate enables another of the at least two images to be visible, the method comprising positioning said phase mask in conjunction with said hologram such that relative movement of said phase mask and said hologram displays said one or another of said images.

A hologram viewing arrangement comprising a pixellated phase mask substrate and a pixellated hologram display substrate, wherein the hologram display substrate is arranged to store data representing at least two images, the arrangement being such that disposing the phase mask in a first position with respect to the display substrate enables one of the at least two images to be visible and disposing the phase mask in a second position with respect to the display substrate enables another of the at least two images to be visible;

• wherein the pixellation axes of the two members are disposed mutually parallel and wherein one of the phase mask substrate and hologram display substrate is constructed and arranged to be subject to a translation with respect to the other of the two substrates parallel to a pixellation axis thereof, to said first and second positions;
• wherein said hologram is calculated to take into account said phase mask such that the hologram reconstructs at least two distinct images when optically combined with the phase mask, and wherein the arrangement is such that disposing the phase mask in a first position with respect to the display substrate enables only one of the at least two images to be visible and disposing the phase mask in a second position with respect to the display substrate enables only another of the at least two images to be visible.