HOLOGRAMS HAVING A STANDARD REFERENCE COLOUR

摘要

Holograms and diffraction gratings are described wherein the presence of a "key-colour" (Magenta) permits an observer to identify the position where all the other colours of the hologram in questio n can be univocally determined. Two set of spectra (50 and 70) are provided such that at a predetermined angle (13) a reference bea m of incident white-light (10) illuminating the holo- gram or diffractin grating composition will cause the observer (11) to see t he color "Magenta" which is to be used as a reference "key-colour".