Yoshinori Akao, Rui Shogenji, Norimichi Tsumura, Masahiro Yamaguchi and
Jun Tanida
OPTICS EXPRESS Vol. 19, No. 4 pp. 3353-3362(2011).
Abstract
In this paper, we propose a method for efficient gonio-imaging of optically
variable devices (OVDs), which are applied as a counterfeit deterrence
for valuable documents. A compound-eye image-capturing system composed
by a microlens array, a signal separator, and an image sensor was used
to capture directionally distributed light from OVDs after being collimated
by a convex lens. Multiple images corresponding to different observation
angles were obtained in the individual eyes of the system, simultaneously
and independently. A demonstration involving a holographic grating provided
100 gonio images that exhibited sensitive color changes of the diffracted
light according to the observation angle.
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