<s>
The	O
rainbow	O
or	O
Benton	B-Algorithm
hologram	I-Algorithm
is	O
a	O
type	O
of	O
hologram	B-Algorithm
invented	O
in	O
1968	O
by	O
Dr.	O
Stephen	O
A	O
.	O
Benton	O
at	O
Polaroid	O
Corporation	O
(	O
later	O
MIT	O
)	O
.	O
</s>
<s>
Rainbow	B-Algorithm
holograms	I-Algorithm
are	O
designed	O
to	O
be	O
viewed	O
under	O
white	O
light	O
illumination	O
,	O
rather	O
than	O
laser	O
light	O
which	O
was	O
required	O
before	O
this	O
.	O
</s>
<s>
The	O
rainbow	O
holography	B-Algorithm
recording	O
process	O
uses	O
a	O
horizontal	O
slit	O
to	O
eliminate	O
vertical	O
parallax	B-Device
in	O
the	O
output	O
image	O
,	O
greatly	O
reducing	O
spectral	O
blur	O
while	O
preserving	O
three-dimensionality	O
for	O
most	O
observers	O
.	O
</s>
<s>
A	O
viewer	O
moving	O
up	O
or	O
down	O
in	O
front	O
of	O
a	O
rainbow	B-Algorithm
hologram	I-Algorithm
sees	O
changing	O
spectral	O
colors	O
rather	O
than	O
different	O
vertical	O
perspectives	O
.	O
</s>
<s>
Because	O
perspective	O
effects	O
are	O
reproduced	O
along	O
one	O
axis	O
only	O
,	O
the	O
subject	O
will	O
appear	O
variously	O
stretched	O
or	O
squashed	O
when	O
the	O
hologram	B-Algorithm
is	O
not	O
viewed	O
at	O
an	O
optimum	O
distance	O
;	O
this	O
distortion	O
may	O
go	O
unnoticed	O
when	O
there	O
is	O
not	O
much	O
depth	O
,	O
but	O
can	O
be	O
severe	O
when	O
the	O
distance	O
of	O
the	O
subject	O
from	O
the	O
plane	O
of	O
the	O
hologram	B-Algorithm
is	O
very	O
substantial	O
.	O
</s>
<s>
Stereopsis	B-Algorithm
and	O
horizontal	O
motion	O
parallax	B-Device
,	O
two	O
relatively	O
powerful	O
cues	O
to	O
depth	O
,	O
are	O
preserved	O
.	O
</s>
<s>
The	O
holograms	B-Algorithm
found	O
on	O
credit	O
cards	O
are	O
examples	O
of	O
rainbow	B-Algorithm
holograms	I-Algorithm
.	O
</s>
<s>
Figure	O
2	O
shows	O
an	O
optical	O
arrangement	O
for	O
making	O
a	O
rainbow	B-Algorithm
hologram	I-Algorithm
.	O
</s>
<s>
The	O
object	O
is	O
illuminated	O
with	O
laser	O
light	O
(	O
not	O
shown	O
in	O
the	O
diagram	O
)	O
,	O
and	O
an	O
image	O
is	O
formed	O
in	O
the	O
plane	O
of	O
the	O
hologram	B-Algorithm
plate	O
used	O
to	O
record	O
the	O
hologram	B-Algorithm
.	O
</s>
<s>
The	O
hologram	B-Algorithm
plate	O
is	O
also	O
illuminated	O
with	O
a	O
reference	O
beam	O
derived	O
from	O
the	O
same	O
laser	O
(	O
not	O
shown	O
in	O
the	O
diagram	O
)	O
,	O
and	O
the	O
interference	O
pattern	O
between	O
object	O
and	O
reference	O
beams	O
is	O
recorded	O
.	O
</s>
<s>
The	O
developed	O
hologram	B-Algorithm
is	O
illuminated	O
by	O
a	O
beam	O
similar	O
to	O
the	O
original	O
reference	O
beam	O
.	O
</s>
<s>
A	O
re-constructed	O
image	O
of	O
the	O
original	O
real	O
image	O
can	O
be	O
seen	O
by	O
an	O
observer	O
located	O
to	O
the	O
right	O
of	O
the	O
hologram	B-Algorithm
.	O
</s>
<s>
If	O
the	O
hologram	B-Algorithm
is	O
illuminated	O
with	O
a	O
laser	O
beam	O
of	O
a	O
different	O
wavelength	O
,	O
the	O
position	O
of	O
the	O
reconstructed	O
image	O
will	O
change	O
.	O
</s>
<s>
When	O
the	O
hologram	B-Algorithm
is	O
illuminated	O
with	O
a	O
white	O
light	O
source	O
directed	O
from	O
the	O
left	O
of	O
the	O
hologram	B-Algorithm
plate	O
,	O
each	O
colour	O
re-constructs	O
a	O
different	O
part	O
of	O
the	O
image	O
at	O
a	O
slightly	O
different	O
angle	O
,	O
so	O
that	O
the	O
whole	O
object	O
is	O
now	O
seen	O
,	O
but	O
with	O
the	O
colour	O
varying	O
in	O
the	O
vertical	O
direction	O
.	O
</s>
<s>
This	O
hologram	B-Algorithm
is	O
a	O
transmission	O
hologram	B-Algorithm
,	O
where	O
the	O
hologram	B-Algorithm
is	O
illuminated	O
on	O
one	O
side	O
,	O
and	O
viewed	O
from	O
the	O
other	O
.	O
</s>
<s>
Illumination	O
and	O
viewing	O
can	O
be	O
done	O
from	O
the	O
same	O
side	O
if	O
the	O
hologram	B-Algorithm
is	O
mounted	O
onto	O
a	O
reflective	O
surface	O
.	O
</s>
<s>
Mass	O
replication	O
of	O
such	O
holograms	B-Algorithm
can	O
be	O
done	O
using	O
an	O
embossing	O
process	O
.	O
</s>
