<s>
An	O
autostereogram	B-Algorithm
is	O
a	O
two-dimensional	O
(	O
2D	O
)	O
image	O
that	O
can	O
create	O
the	O
optical	O
illusion	O
of	O
a	O
three-dimensional	O
(	O
3D	O
)	O
scene	O
.	O
</s>
<s>
Autostereograms	B-Algorithm
use	O
only	O
one	O
image	O
to	O
accomplish	O
the	O
effect	O
while	O
normal	O
stereograms	B-Algorithm
require	O
two	O
.	O
</s>
<s>
The	O
3D	O
scene	O
in	O
an	O
autostereogram	B-Algorithm
is	O
often	O
unrecognizable	O
until	O
it	O
is	O
viewed	O
properly	O
,	O
unlike	O
typical	O
stereograms	B-Algorithm
.	O
</s>
<s>
Viewing	O
any	O
kind	O
of	O
stereogram	B-Algorithm
properly	O
may	O
cause	O
the	O
viewer	O
to	O
experience	O
vergence-accommodation	O
conflict	O
.	O
</s>
<s>
The	O
optical	O
illusion	O
of	O
an	O
autostereogram	B-Algorithm
is	O
one	O
of	O
depth	O
perception	O
and	O
involves	O
stereopsis	B-Algorithm
:	O
depth	O
perception	O
arising	O
from	O
the	O
different	O
perspective	O
each	O
eye	O
has	O
of	O
a	O
three-dimensional	O
scene	O
,	O
called	O
binocular	O
parallax	B-Device
.	O
</s>
<s>
Individuals	O
with	O
disordered	O
binocular	B-Algorithm
vision	I-Algorithm
and	O
who	O
cannot	O
perceive	O
depth	O
may	O
require	O
a	O
wiggle	B-Algorithm
stereogram	I-Algorithm
to	O
achieve	O
a	O
similar	O
effect	O
.	O
</s>
<s>
The	O
simplest	O
type	O
of	O
autostereogram	B-Algorithm
consists	O
of	O
a	O
horizontally	O
repeating	O
pattern	O
with	O
small	O
changes	O
throughout	O
that	O
looks	O
like	O
wallpaper	O
.	O
</s>
<s>
When	O
viewed	O
with	O
proper	O
vergence	B-Algorithm
,	O
the	O
repeating	O
patterns	O
appear	O
to	O
float	O
above	O
or	O
below	O
the	O
background	O
.	O
</s>
<s>
The	O
well-known	O
Magic	B-General_Concept
Eye	I-General_Concept
books	O
feature	O
another	O
type	O
of	O
autostereogram	B-Algorithm
called	O
a	O
random	O
dot	O
autostereogram	B-Algorithm
,	O
similar	O
to	O
the	O
first	O
example	O
,	O
above	O
.	O
</s>
<s>
In	O
this	O
type	O
of	O
autostereogram	B-Algorithm
,	O
every	O
pixel	B-Algorithm
in	O
the	O
image	O
is	O
computed	O
from	O
a	O
pattern	O
strip	O
and	O
a	O
depth	O
map	O
.	O
</s>
<s>
A	O
hidden	O
3D	O
scene	O
emerges	O
when	O
the	O
image	O
is	O
viewed	O
with	O
the	O
correct	O
vergence	B-Algorithm
.	O
</s>
<s>
Unlike	O
normal	O
stereograms	B-Algorithm
,	O
autostereograms	B-Algorithm
do	O
not	O
require	O
the	O
use	O
of	O
a	O
stereoscope	B-Algorithm
.	O
</s>
<s>
A	O
stereoscope	B-Algorithm
presents	O
2D	O
images	O
of	O
the	O
same	O
object	O
from	O
slightly	O
different	O
angles	O
to	O
the	O
left	O
eye	O
and	O
the	O
right	O
eye	O
,	O
allowing	O
us	O
to	O
reconstruct	O
the	O
original	O
object	O
via	O
binocular	O
disparity	O
.	O
</s>
<s>
When	O
viewed	O
with	O
the	O
proper	O
vergence	B-Algorithm
,	O
an	O
autostereogram	B-Algorithm
does	O
the	O
same	O
,	O
the	O
binocular	O
disparity	O
existing	O
in	O
adjacent	O
parts	O
of	O
the	O
repeating	O
2D	O
patterns	O
.	O
</s>
<s>
There	O
are	O
two	O
ways	O
an	O
autostereogram	B-Algorithm
can	O
be	O
viewed	O
:	O
wall-eyed	O
and	O
cross-eyed	O
.	O
</s>
<s>
Most	O
autostereograms	B-Algorithm
(	O
including	O
those	O
in	O
this	O
article	O
)	O
are	O
designed	O
to	O
be	O
viewed	O
in	O
only	O
one	O
way	O
,	O
which	O
is	O
usually	O
wall-eyed	O
.	O
</s>
<s>
This	O
is	O
an	O
early	O
example	O
of	O
dissociating	O
vergence	B-Algorithm
from	O
accommodation	O
—	O
a	O
necessary	O
ability	O
for	O
seeing	O
autostereograms	B-Algorithm
.	O
</s>
<s>
It	O
was	O
not	O
until	O
1838	O
that	O
the	O
Charles	O
Wheatstone	O
published	O
an	O
example	O
of	O
cooperation	O
between	O
the	O
images	O
in	O
the	O
two	O
eyes	O
:	O
stereopsis	B-Algorithm
(	O
binocular	B-Algorithm
depth	I-Algorithm
perception	I-Algorithm
)	O
.	O
</s>
<s>
He	O
supported	O
his	O
explanation	O
by	O
showing	O
flat	O
,	O
two-dimensional	O
pictures	O
with	O
such	O
horizontal	O
differences	O
,	O
stereograms	B-Algorithm
,	O
separately	O
to	O
the	O
left	O
and	O
right	O
eyes	O
through	O
a	O
stereoscope	B-Algorithm
he	O
invented	O
based	O
on	O
mirrors	O
.	O
</s>
<s>
In	O
1844	O
,	O
David	O
Brewster	O
discovered	O
the	O
"	O
wallpaper	B-Algorithm
effect	I-Algorithm
"	O
.	O
</s>
<s>
He	O
noticed	O
that	O
when	O
he	O
stared	O
at	O
repeated	O
patterns	O
in	O
wallpapers	O
while	O
varying	O
his	O
vergence	B-Algorithm
,	O
he	O
could	O
see	O
them	O
either	O
behind	O
the	O
wall	O
(	O
with	O
wall-eyed	O
vergence	B-Algorithm
)	O
or	O
in	O
front	O
of	O
the	O
wall	O
(	O
with	O
cross-eyed	O
vergence	B-Algorithm
)	O
.	O
</s>
<s>
This	O
is	O
the	O
basis	O
of	O
wallpaper-style	O
autostereograms	B-Algorithm
.	O
</s>
<s>
In	O
1939	O
Boris	O
Kompaneysky	O
published	O
the	O
first	O
,	O
random-dot	B-Algorithm
stereogram	I-Algorithm
containing	O
a	O
hand-drawn	O
image	O
of	O
the	O
face	O
of	O
Venus	O
,	O
intended	O
to	O
be	O
viewed	O
with	O
a	O
device	O
.	O
</s>
<s>
In	O
1959	O
,	O
Bela	O
Julesz	O
,	O
vision	O
scientist	O
,	O
psychologist	O
,	O
and	O
MacArthur	O
Fellow	O
,	O
invented	O
random	B-Algorithm
dot	I-Algorithm
stereograms	I-Algorithm
while	O
working	O
at	O
Bell	O
Laboratories	O
on	O
recognizing	O
camouflaged	O
objects	O
from	O
aerial	O
pictures	O
taken	O
by	O
spy	O
planes	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
many	O
vision	O
scientists	O
assumed	O
that	O
stereopsis	B-Algorithm
required	O
prior	O
analysis	O
of	O
visible	O
contours	O
of	O
images	O
in	O
each	O
eye	O
,	O
but	O
Julesz	O
showed	O
it	O
occurs	O
with	O
images	O
with	O
no	O
such	O
visible	O
contours	O
in	O
each	O
of	O
the	O
eyes	O
.	O
</s>
<s>
The	O
contours	O
of	O
the	O
depth	O
object	O
become	O
visible	O
only	O
after	O
stereopsis	B-Algorithm
had	O
processed	O
the	O
differences	O
in	O
the	O
horizontal	O
positions	O
of	O
dots	O
in	O
the	O
two	O
eyes	O
 '	O
images	O
.	O
</s>
<s>
Japanese	O
designer	O
Masayuki	O
Ito	O
,	O
following	O
Julesz	O
,	O
created	O
a	O
single	B-Algorithm
image	I-Algorithm
stereogram	I-Algorithm
in	O
1970	O
and	O
Swiss	O
painter	O
Alfons	O
Schilling	O
created	O
a	O
handmade	O
single-image	B-Algorithm
stereogram	I-Algorithm
in	O
1974	O
,	O
after	O
creating	O
more	O
than	O
one	O
viewer	O
and	O
meeting	O
with	O
Julesz	O
.	O
</s>
<s>
Having	O
experience	O
with	O
stereo	O
imaging	O
in	O
holography	B-Algorithm
,	O
lenticular	O
photography	O
,	O
and	O
vectography	B-Algorithm
,	O
he	O
developed	O
a	O
random-dot	O
method	O
based	O
on	O
closely	O
spaced	O
vertical	O
lines	O
in	O
parallax	B-Device
.	O
</s>
<s>
In	O
1979	O
,	O
Christopher	O
Tyler	O
of	O
Smith-Kettlewell	O
Institute	O
,	O
a	O
student	O
of	O
Julesz	O
and	O
a	O
visual	O
psychophysicist	O
,	O
combined	O
the	O
theories	O
behind	O
single-image	O
wallpaper	O
stereograms	B-Algorithm
and	O
random-dot	B-Algorithm
stereograms	I-Algorithm
(	O
the	O
work	O
of	O
Julesz	O
and	O
Schilling	O
)	O
to	O
create	O
the	O
first	O
black-and-white	O
random-dot	B-Algorithm
autostereogram	I-Algorithm
with	O
the	O
assistance	O
of	O
computer	O
programmer	O
Maureen	O
Clarke	O
using	O
Apple	B-Device
II	I-Device
and	O
BASIC	O
.	O
</s>
<s>
Stork	O
and	O
Rocca	O
published	O
the	O
first	O
scholarly	O
paper	O
and	O
provided	O
software	O
for	O
generating	O
random-dot	B-Algorithm
stereograms	I-Algorithm
.	O
</s>
<s>
This	O
type	O
of	O
autostereogram	B-Algorithm
allows	O
a	O
person	O
to	O
see	O
3D	O
shapes	O
from	O
a	O
single	O
2D	O
image	O
without	O
the	O
aid	O
of	O
optical	O
equipment	O
.	O
</s>
<s>
In	O
1991	O
computer	O
programmer	O
Tom	O
Baccei	O
and	O
artist	O
Cheri	O
Smith	O
created	O
the	O
first	O
color	O
random-dot	B-Algorithm
autostereograms	I-Algorithm
,	O
later	O
marketed	O
as	O
Magic	B-General_Concept
Eye	I-General_Concept
.	O
</s>
<s>
A	O
computer	O
procedure	O
that	O
extracts	O
back	O
the	O
hidden	O
geometry	O
out	O
of	O
an	O
autostereogram	B-Algorithm
image	O
was	O
described	O
by	O
Ron	O
Kimmel	O
.	O
</s>
<s>
In	O
the	O
late	O
90	O
's	O
many	O
children	O
's	O
magazines	O
featured	O
autostereograms	B-Algorithm
.	O
</s>
<s>
Even	O
gaming	O
magazines	O
like	O
Nintendo	B-Application
Power	I-Application
had	O
a	O
section	O
specifically	O
made	O
for	O
these	O
illusions	O
.	O
</s>
<s>
Stereopsis	B-Algorithm
,	O
or	O
stereo	B-Algorithm
vision	I-Algorithm
,	O
is	O
the	O
visual	O
blending	O
of	O
two	O
similar	O
but	O
not	O
identical	O
images	O
into	O
one	O
,	O
with	O
resulting	O
visual	O
perception	O
of	O
solidity	O
and	O
depth	O
.	O
</s>
<s>
In	O
the	O
human	O
brain	O
,	O
stereopsis	B-Algorithm
results	O
from	O
complex	O
mechanisms	O
that	O
form	O
a	O
three-dimensional	O
impression	O
by	O
matching	O
each	O
point	O
(	O
or	O
set	O
of	O
points	O
)	O
in	O
one	O
eye	O
's	O
view	O
with	O
the	O
equivalent	O
point	O
(	O
or	O
set	O
of	O
points	O
)	O
in	O
the	O
other	O
eye	O
's	O
view	O
.	O
</s>
<s>
Autostereograms	B-Algorithm
use	O
this	O
dependence	O
of	O
depth	O
on	O
spacing	O
to	O
create	O
three-dimensional	O
images	O
.	O
</s>
<s>
People	O
who	O
have	O
never	O
been	O
able	O
to	O
perceive	O
3D	O
shapes	O
hidden	O
within	O
an	O
autostereogram	B-Algorithm
find	O
it	O
hard	O
to	O
understand	O
remarks	O
such	O
as	O
,	O
"	O
the	O
3D	B-Algorithm
image	I-Algorithm
will	O
just	O
pop	O
out	O
of	O
the	O
background	O
,	O
after	O
you	O
stare	O
at	O
the	O
picture	O
long	O
enough	O
"	O
,	O
or	O
"	O
the	O
3D	O
objects	O
will	O
just	O
emerge	O
from	O
the	O
background	O
"	O
.	O
</s>
<s>
It	O
helps	O
to	O
illustrate	O
how	O
3D	B-Algorithm
images	I-Algorithm
"	O
emerge	O
"	O
from	O
the	O
background	O
from	O
a	O
second	O
viewer	O
's	O
perspective	O
.	O
</s>
<s>
If	O
the	O
virtual	O
3D	O
objects	O
reconstructed	O
by	O
the	O
autostereogram	B-Algorithm
viewer	O
's	O
brain	O
were	O
real	O
objects	O
,	O
a	O
second	O
viewer	O
observing	O
the	O
scene	O
from	O
the	O
side	O
would	O
see	O
these	O
objects	O
floating	O
in	O
the	O
air	O
above	O
the	O
background	O
image	O
.	O
</s>
<s>
The	O
3D	O
effects	O
in	O
the	O
example	O
autostereogram	B-Algorithm
are	O
created	O
by	O
repeating	O
the	O
tiger	O
rider	O
icons	O
every	O
140	O
pixels	B-Algorithm
on	O
the	O
background	O
plane	O
,	O
the	O
shark	O
rider	O
icons	O
every	O
130	O
pixels	B-Algorithm
on	O
the	O
second	O
plane	O
,	O
and	O
the	O
tiger	O
icons	O
every	O
120	O
pixels	B-Algorithm
on	O
the	O
highest	O
plane	O
.	O
</s>
<s>
This	O
repeat	O
distance	O
is	O
referred	O
to	O
as	O
the	O
depth	O
or	O
z-axis	O
value	O
of	O
a	O
particular	O
pattern	O
in	O
the	O
autostereogram	B-Algorithm
.	O
</s>
<s>
thumb|270px|This	O
picture	O
illustrates	O
how	O
3D	O
shapes	O
from	O
an	O
autostereogram	B-Algorithm
"	O
emerge	O
"	O
from	O
the	O
background	O
plane	O
,	O
when	O
the	O
autostereogram	B-Algorithm
is	O
viewed	O
with	O
proper	O
eye	O
divergence	O
.	O
</s>
<s>
thumb|270px|Depth	O
or	O
z-axis	O
values	O
are	O
proportional	O
to	O
pixel	B-Algorithm
shifts	O
in	O
the	O
autostereogram	B-Algorithm
.	O
</s>
<s>
An	O
autostereogram	B-Algorithm
may	O
contain	O
some	O
50	O
tigers	O
of	O
varying	O
size	O
,	O
repeated	O
at	O
different	O
intervals	O
against	O
a	O
complex	O
,	O
repeated	O
background	O
.	O
</s>
<s>
thumb|350px|Depth	O
map	O
example	O
autostereogram	B-Algorithm
:	O
Patterns	O
in	O
this	O
autostereogram	B-Algorithm
appear	O
at	O
different	O
depth	O
across	O
each	O
row	O
.	O
</s>
<s>
thumb|center|200px|Depth	O
map	O
greyscale	O
example	O
autostereogram	B-Algorithm
:	O
The	O
black	O
,	O
gray	O
and	O
white	O
colors	O
in	O
the	O
background	O
represent	O
a	O
depth	O
map	O
showing	O
changes	O
in	O
depth	O
across	O
row	O
.	O
</s>
<s>
Autostereograms	B-Algorithm
where	O
patterns	O
in	O
a	O
particular	O
row	O
are	O
repeated	O
horizontally	O
with	O
the	O
same	O
spacing	O
can	O
be	O
read	O
either	O
cross-eyed	O
or	O
wall-eyed	O
.	O
</s>
<s>
In	O
such	O
autostereograms	B-Algorithm
,	O
both	O
types	O
of	O
reading	O
will	O
produce	O
similar	O
depth	O
interpretation	O
,	O
with	O
the	O
exception	O
that	O
the	O
cross-eyed	O
reading	O
reverses	O
the	O
depth	O
(	O
images	O
that	O
once	O
popped	O
out	O
are	O
now	O
pushed	O
in	O
)	O
.	O
</s>
<s>
An	O
autostereogram	B-Algorithm
with	O
varying	O
intervals	O
between	O
icons	O
across	O
a	O
row	O
presents	O
these	O
icons	O
at	O
different	O
depth	O
planes	O
to	O
the	O
viewer	O
.	O
</s>
<s>
These	O
types	O
of	O
autostereograms	B-Algorithm
are	O
designed	O
to	O
be	O
read	O
in	O
only	O
one	O
way	O
,	O
either	O
cross-eyed	O
or	O
wall-eyed	O
.	O
</s>
<s>
All	O
autostereograms	B-Algorithm
in	O
this	O
article	O
are	O
encoded	O
for	O
wall-eyed	O
viewing	O
,	O
unless	O
specifically	O
marked	O
otherwise	O
.	O
</s>
<s>
An	O
autostereogram	B-Algorithm
encoded	O
for	O
wall-eyed	O
viewing	O
will	O
produce	O
inverse	O
patterns	O
when	O
viewed	O
cross-eyed	O
,	O
and	O
vice	O
versa	O
.	O
</s>
<s>
Most	O
Magic	B-General_Concept
Eye	I-General_Concept
pictures	O
are	O
also	O
designed	O
for	O
wall-eyed	O
viewing	O
.	O
</s>
<s>
The	O
wall-eyed	O
depth	O
map	O
example	O
autostereogram	B-Algorithm
to	O
the	O
right	O
encodes	O
3	O
planes	O
across	O
the	O
x-axis	O
.	O
</s>
<s>
Starting	O
with	O
a	O
background	O
plane	O
where	O
icons	O
are	O
spaced	O
at	O
140	O
pixels	B-Algorithm
,	O
one	O
can	O
raise	O
a	O
particular	O
icon	O
by	O
shifting	O
it	O
a	O
certain	O
number	O
of	O
pixels	B-Algorithm
to	O
the	O
left	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
middle	O
plane	O
is	O
created	O
by	O
shifting	O
an	O
icon	O
10	O
pixels	B-Algorithm
to	O
the	O
left	O
,	O
effectively	O
creating	O
a	O
spacing	O
consisting	O
of	O
130	O
pixels	B-Algorithm
.	O
</s>
<s>
In	O
this	O
autostereogram	B-Algorithm
,	O
patterns	O
become	O
smaller	O
and	O
smaller	O
down	O
the	O
y-axis	O
,	O
until	O
they	O
look	O
like	O
random	O
dots	O
.	O
</s>
<s>
The	O
distance	O
relationship	O
between	O
any	O
pixel	B-Algorithm
and	O
its	O
counterpart	O
in	O
the	O
equivalent	O
pattern	O
to	O
the	O
left	O
can	O
be	O
expressed	O
in	O
a	O
depth	O
map	O
.	O
</s>
<s>
A	O
depth	O
map	O
is	O
simply	O
a	O
grayscale	O
image	O
which	O
represents	O
the	O
distance	O
between	O
a	O
pixel	B-Algorithm
and	O
its	O
left	O
counterpart	O
using	O
a	O
grayscale	O
value	O
between	O
black	O
and	O
white	O
.	O
</s>
<s>
Using	O
this	O
convention	O
,	O
a	O
grayscale	O
depth	O
map	O
for	O
the	O
example	O
autostereogram	B-Algorithm
can	O
be	O
created	O
with	O
black	O
,	O
gray	O
and	O
white	O
representing	O
shifts	O
of	O
0	O
pixels	B-Algorithm
,	O
10	O
pixels	B-Algorithm
and	O
20	O
pixels	B-Algorithm
,	O
respectively	O
as	O
shown	O
in	O
the	O
greyscale	O
example	O
autostereogram	B-Algorithm
.	O
</s>
<s>
A	O
depth	O
map	O
is	O
the	O
key	O
to	O
creation	O
of	O
random-dot	B-Algorithm
autostereograms	I-Algorithm
.	O
</s>
<s>
A	O
computer	O
program	O
can	O
take	O
a	O
depth	O
map	O
and	O
an	O
accompanying	O
pattern	O
image	O
to	O
produce	O
an	O
autostereogram	B-Algorithm
.	O
</s>
<s>
Conceptually	O
,	O
at	O
every	O
pixel	B-Algorithm
in	O
the	O
output	O
image	O
,	O
the	O
program	O
looks	O
up	O
the	O
grayscale	O
value	O
of	O
the	O
equivalent	O
pixel	B-Algorithm
in	O
the	O
depth	O
map	O
image	O
,	O
and	O
uses	O
this	O
value	O
to	O
determine	O
the	O
amount	O
of	O
horizontal	O
shift	O
required	O
for	O
the	O
pixel	B-Algorithm
.	O
</s>
<s>
One	O
way	O
to	O
accomplish	O
this	O
is	O
to	O
make	O
the	O
program	O
scan	O
every	O
line	O
in	O
the	O
output	O
image	O
pixel-by-pixel	O
from	O
left	O
to	O
right	O
.	O
</s>
<s>
It	O
seeds	O
the	O
first	O
series	O
of	O
pixels	B-Algorithm
in	O
a	O
row	O
from	O
the	O
pattern	O
image	O
.	O
</s>
<s>
Then	O
it	O
consults	O
the	O
depth	O
map	O
to	O
retrieve	O
appropriate	O
shift	O
values	O
for	O
subsequent	O
pixels	B-Algorithm
.	O
</s>
<s>
For	O
every	O
pixel	B-Algorithm
,	O
it	O
subtracts	O
the	O
shift	O
from	O
the	O
width	O
of	O
the	O
pattern	O
image	O
to	O
arrive	O
at	O
a	O
repeat	O
interval	O
.	O
</s>
<s>
It	O
uses	O
this	O
repeat	O
interval	O
to	O
look	O
up	O
the	O
color	O
of	O
the	O
counterpart	O
pixel	B-Algorithm
to	O
the	O
left	O
and	O
uses	O
its	O
color	O
as	O
the	O
new	O
pixel	B-Algorithm
's	O
own	O
color	O
.	O
</s>
<s>
thumb|250px|Three	O
raised	O
rectangles	O
appear	O
on	O
different	O
depth	O
planes	O
in	O
this	O
autostereogram	B-Algorithm
.	O
</s>
<s>
(	O
10px	O
)	O
thumb|250px|Every	O
pixel	B-Algorithm
in	O
an	O
autostereogram	B-Algorithm
obeys	O
the	O
distance	O
interval	O
specified	O
by	O
the	O
depth	O
map	O
.	O
</s>
<s>
Unlike	O
the	O
simple	O
depth	O
planes	O
created	O
by	O
simple	O
wallpaper	B-Algorithm
autostereograms	I-Algorithm
,	O
subtle	O
changes	O
in	O
spacing	O
specified	O
by	O
the	O
depth	O
map	O
can	O
create	O
the	O
illusion	O
of	O
smooth	O
gradients	O
in	O
distance	O
.	O
</s>
<s>
This	O
is	O
possible	O
because	O
the	O
grayscale	O
depth	O
map	O
allows	O
individual	O
pixels	B-Algorithm
to	O
be	O
placed	O
on	O
one	O
of	O
2n	O
depth	O
planes	O
,	O
where	O
n	O
is	O
the	O
number	O
of	O
bits	O
used	O
by	O
each	O
pixel	B-Algorithm
in	O
the	O
depth	O
map	O
.	O
</s>
<s>
In	O
practice	O
,	O
the	O
total	O
number	O
of	O
depth	O
planes	O
is	O
determined	O
by	O
the	O
number	O
of	O
pixels	B-Algorithm
used	O
for	O
the	O
width	O
of	O
the	O
pattern	O
image	O
.	O
</s>
<s>
Each	O
grayscale	O
value	O
must	O
be	O
translated	O
into	O
pixel	B-Algorithm
space	O
in	O
order	O
to	O
shift	O
pixels	B-Algorithm
in	O
the	O
final	O
autostereogram	B-Algorithm
.	O
</s>
<s>
When	O
the	O
autostereogram	B-Algorithm
is	O
viewed	O
with	O
proper	O
viewing	O
technique	O
,	O
a	O
hidden	O
3D	O
scene	O
emerges	O
.	O
</s>
<s>
Autostereograms	B-Algorithm
of	O
this	O
form	O
are	O
known	O
as	O
Random	O
Dot	O
Autostereograms	B-Algorithm
.	O
</s>
<s>
A	O
big	O
area	O
painted	O
with	O
monotonic	O
color	O
without	O
change	O
in	O
hue	B-Language
and	O
brightness	O
does	O
not	O
lend	O
itself	O
to	O
pixel	B-Algorithm
shifting	O
,	O
as	O
the	O
result	O
of	O
the	O
horizontal	O
shift	O
is	O
identical	O
to	O
the	O
original	O
patch	O
.	O
</s>
<s>
The	O
following	O
depth	O
map	O
of	O
a	O
shark	O
with	O
smooth	O
gradient	O
produces	O
a	O
perfectly	O
readable	O
autostereogram	B-Algorithm
,	O
even	O
though	O
the	O
2D	O
image	O
contains	O
small	O
monotonic	O
areas	O
;	O
the	O
brain	O
is	O
able	O
to	O
recognize	O
these	O
small	O
gaps	O
and	O
fill	O
in	O
the	O
blanks	O
(	O
illusory	O
contours	O
)	O
.	O
</s>
<s>
While	O
intelligible	O
,	O
repeated	O
patterns	O
are	O
used	O
instead	O
of	O
random	O
dots	O
,	O
this	O
type	O
of	O
autostereogram	B-Algorithm
is	O
still	O
known	O
by	O
many	O
as	O
a	O
Random	O
Dot	O
Autostereogram	B-Algorithm
,	O
because	O
it	O
is	O
created	O
using	O
the	O
same	O
process	O
.	O
</s>
<s>
thumb|left|250px|The	O
3D	O
shark	O
in	O
this	O
random-dot	B-Algorithm
autostereogram	I-Algorithm
has	O
a	O
smooth	O
,	O
round	O
shape	O
due	O
to	O
the	O
use	O
of	O
depth	O
map	O
with	O
smooth	O
gradient	O
.	O
</s>
<s>
When	O
a	O
series	O
of	O
autostereograms	B-Algorithm
are	O
shown	O
one	O
after	O
another	O
,	O
in	O
the	O
same	O
way	O
moving	O
pictures	O
are	O
shown	O
,	O
the	O
brain	O
perceives	O
an	O
animated	O
autostereogram	B-Algorithm
.	O
</s>
<s>
If	O
all	O
autostereograms	B-Algorithm
in	O
the	O
animation	O
are	O
produced	O
using	O
the	O
same	O
background	O
pattern	O
,	O
it	O
is	O
often	O
possible	O
to	O
see	O
faint	O
outlines	O
of	O
parts	O
of	O
the	O
moving	O
3D	O
object	O
in	O
the	O
2D	O
autostereogram	B-Algorithm
image	O
without	O
wall-eyed	O
viewing	O
;	O
the	O
constantly	O
shifting	O
pixels	B-Algorithm
of	O
the	O
moving	O
object	O
can	O
be	O
clearly	O
distinguished	O
from	O
the	O
static	O
background	O
plane	O
.	O
</s>
<s>
To	O
eliminate	O
this	O
side	O
effect	O
,	O
animated	O
autostereograms	B-Algorithm
often	O
use	O
shifting	O
background	O
in	O
order	O
to	O
disguise	O
the	O
moving	O
parts	O
.	O
</s>
<s>
When	O
a	O
regular	O
repeating	O
pattern	O
is	O
viewed	O
on	O
a	O
CRT	B-Device
monitor	I-Device
as	O
if	O
it	O
were	O
a	O
wallpaper	B-Algorithm
autostereogram	I-Algorithm
,	O
it	O
is	O
usually	O
possible	O
to	O
see	O
depth	O
ripples	O
.	O
</s>
<s>
This	O
can	O
also	O
be	O
seen	O
in	O
the	O
background	O
to	O
a	O
static	O
,	O
random-dot	B-Algorithm
autostereogram	I-Algorithm
.	O
</s>
<s>
On	O
a	O
TFT	B-Device
LCD	I-Device
,	O
which	O
functions	O
differently	O
,	O
this	O
does	O
not	O
occur	O
and	O
the	O
effect	O
is	O
not	O
present	O
.	O
</s>
<s>
Higher	O
quality	O
CRT	B-Device
displays	I-Device
also	O
have	O
better	O
linearity	O
and	O
exhibit	O
less	O
or	O
none	O
of	O
this	O
effect	O
.	O
</s>
<s>
Much	O
advice	O
exists	O
about	O
seeing	O
the	O
intended	O
three-dimensional	O
image	O
in	O
an	O
autostereogram	B-Algorithm
.	O
</s>
<s>
While	O
some	O
people	O
may	O
quickly	O
see	O
the	O
3D	B-Algorithm
image	I-Algorithm
in	O
an	O
autostereogram	B-Algorithm
with	O
little	O
effort	O
,	O
others	O
must	O
learn	O
to	O
train	O
their	O
eyes	O
to	O
decouple	O
eye	O
convergence	O
from	O
lens	O
focusing	O
.	O
</s>
<s>
Not	O
every	O
person	O
can	O
see	O
the	O
3D	O
illusion	O
in	O
autostereograms	B-Algorithm
.	O
</s>
<s>
Because	O
autostereograms	B-Algorithm
are	O
constructed	O
based	O
on	O
stereo	B-Algorithm
vision	I-Algorithm
,	O
persons	O
with	O
a	O
variety	O
of	O
visual	O
impairments	O
,	O
even	O
those	O
affecting	O
only	O
one	O
eye	O
,	O
are	O
unable	O
to	O
see	O
the	O
three-dimensional	O
images	O
.	O
</s>
<s>
Children	O
with	O
poor	O
or	O
dysfunctional	O
eyesight	O
during	O
a	O
critical	O
period	O
in	O
childhood	O
may	O
grow	O
up	O
stereoblind	B-Algorithm
,	O
as	O
their	O
brains	O
are	O
not	O
stimulated	O
by	O
stereo	O
images	O
during	O
the	O
critical	O
period	O
.	O
</s>
<s>
If	O
such	O
a	O
vision	O
problem	O
is	O
not	O
corrected	O
in	O
early	O
childhood	O
,	O
the	O
damage	O
becomes	O
permanent	O
and	O
the	O
adult	O
will	O
never	O
be	O
able	O
to	O
see	O
autostereograms	B-Algorithm
.	O
</s>
<s>
For	O
objects	O
relatively	O
close	O
to	O
the	O
eyes	O
,	O
binocular	B-Algorithm
vision	I-Algorithm
plays	O
an	O
important	O
role	O
in	O
depth	O
perception	O
.	O
</s>
<s>
Binocular	B-Algorithm
vision	I-Algorithm
allows	O
the	O
brain	O
to	O
create	O
a	O
single	O
Cyclopean	O
image	O
and	O
to	O
attach	O
a	O
depth	O
level	O
to	O
each	O
point	O
in	O
it	O
.	O
</s>
<s>
The	O
brain	O
uses	O
coordinate	O
shift	O
(	O
also	O
known	O
as	O
parallax	B-Device
)	O
of	O
matched	O
objects	O
to	O
identify	O
depth	O
of	O
these	O
objects	O
.	O
</s>
<s>
The	O
depth	O
level	O
of	O
each	O
point	O
in	O
the	O
combined	O
image	O
can	O
be	O
represented	O
by	O
a	O
grayscale	O
pixel	B-Algorithm
on	O
a	O
2D	O
image	O
,	O
for	O
the	O
benefit	O
of	O
the	O
reader	O
.	O
</s>
<s>
Thus	O
,	O
the	O
way	O
the	O
brain	O
perceives	O
depth	O
using	O
binocular	B-Algorithm
vision	I-Algorithm
can	O
be	O
captured	O
by	O
a	O
depth	O
map	O
(	O
Cyclopean	O
image	O
)	O
painted	O
based	O
on	O
coordinate	O
shift	O
.	O
</s>
<s>
As	O
with	O
any	O
camera	O
except	O
pinhole	B-Algorithm
cameras	I-Algorithm
,	O
it	O
needs	O
to	O
focus	O
light	O
rays	O
entering	O
through	O
the	O
iris	O
(	O
aperture	B-General_Concept
in	O
a	O
camera	O
)	O
so	O
that	O
they	O
focus	O
on	O
a	O
single	O
point	O
on	O
the	O
retina	O
in	O
order	O
to	O
produce	O
a	O
sharp	O
image	O
.	O
</s>
<s>
Stereo-vision	O
based	O
on	O
parallax	B-Device
allows	O
the	O
brain	O
to	O
calculate	O
depths	O
of	O
objects	O
relative	O
to	O
the	O
point	O
of	O
convergence	O
.	O
</s>
<s>
To	O
see	O
a	O
man-made	O
picture	O
such	O
as	O
an	O
autostereogram	B-Algorithm
where	O
patterns	O
are	O
repeated	O
horizontally	O
,	O
however	O
,	O
decoupling	O
of	O
focusing	O
from	O
convergence	O
is	O
crucial	O
.	O
</s>
<s>
By	O
focusing	O
the	O
lenses	O
on	O
a	O
nearby	O
autostereogram	B-Algorithm
where	O
patterns	O
are	O
repeated	O
and	O
by	O
converging	O
the	O
eyeballs	O
at	O
a	O
distant	O
point	O
behind	O
the	O
autostereogram	B-Algorithm
image	O
,	O
one	O
can	O
trick	O
the	O
brain	O
into	O
seeing	O
3D	B-Algorithm
images	I-Algorithm
.	O
</s>
<s>
This	O
type	O
of	O
visualization	O
is	O
known	O
as	O
wall-eyed	O
viewing	O
,	O
because	O
the	O
eyeballs	O
adopt	O
a	O
wall-eyed	O
convergence	O
on	O
a	O
distant	O
plane	O
,	O
even	O
though	O
the	O
autostereogram	B-Algorithm
image	O
is	O
actually	O
closer	O
to	O
the	O
eyes	O
.	O
</s>
<s>
Because	O
the	O
two	O
eyeballs	O
converge	O
on	O
a	O
plane	O
farther	O
away	O
,	O
the	O
perceived	O
location	O
of	O
the	O
imaginary	O
object	O
is	O
behind	O
the	O
autostereogram	B-Algorithm
.	O
</s>
<s>
The	O
imaginary	O
object	O
also	O
appears	O
bigger	O
than	O
the	O
patterns	O
on	O
the	O
autostereogram	B-Algorithm
because	O
of	O
foreshortening	O
.	O
</s>
<s>
The	O
following	O
autostereogram	B-Algorithm
shows	O
three	O
rows	O
of	O
repeated	O
patterns	O
.	O
</s>
<s>
When	O
the	O
autostereogram	B-Algorithm
is	O
correctly	O
interpreted	O
by	O
the	O
brain	O
using	O
wall-eyed	O
viewing	O
,	O
and	O
one	O
stares	O
at	O
the	O
dolphin	O
in	O
the	O
middle	O
of	O
the	O
visual	O
field	O
,	O
the	O
brain	O
should	O
see	O
two	O
sets	O
of	O
flickering	O
lines	O
,	O
as	O
a	O
result	O
of	O
binocular	O
rivalry	O
.	O
</s>
<s>
thumb|left|200px|The	O
two	O
black	O
lines	O
in	O
this	O
Autostereogram	B-Algorithm
help	O
viewers	O
establish	O
proper	O
wall-eyed	O
viewing	O
,	O
see	O
right	O
.	O
</s>
<s>
While	O
there	O
are	O
six	O
dolphin	O
patterns	O
in	O
the	O
autostereogram	B-Algorithm
,	O
the	O
brain	O
should	O
see	O
seven	O
"	O
apparent	O
"	O
dolphins	O
on	O
the	O
plane	O
of	O
the	O
autostereogram	B-Algorithm
.	O
</s>
<s>
In	O
the	O
autostereogram	B-Algorithm
of	O
three	O
rows	O
of	O
cubes	O
,	O
while	O
all	O
cubes	O
have	O
the	O
same	O
physical	O
2D	O
dimensions	O
,	O
the	O
ones	O
on	O
the	O
top	O
row	O
appear	O
bigger	O
,	O
because	O
they	O
are	O
perceived	O
as	O
farther	O
away	O
than	O
the	O
cubes	O
on	O
the	O
second	O
and	O
third	O
rows	O
.	O
</s>
<s>
If	O
one	O
has	O
two	O
eyes	O
,	O
fairly	O
healthy	O
eyesight	O
,	O
and	O
no	O
neurological	O
conditions	O
which	O
prevent	O
the	O
perception	O
of	O
depth	O
,	O
then	O
one	O
is	O
capable	O
of	O
learning	O
to	O
see	O
the	O
images	O
within	O
autostereograms	B-Algorithm
.	O
</s>
<s>
The	O
more	O
the	O
eye	O
resembles	O
a	O
pinhole	B-Algorithm
camera	I-Algorithm
,	O
the	O
less	O
it	O
depends	O
on	O
focusing	O
through	O
the	O
lens	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
degree	O
of	O
decoupling	O
between	O
focusing	O
and	O
convergence	O
needed	O
to	O
visualize	O
an	O
autostereogram	B-Algorithm
is	O
reduced	O
.	O
</s>
<s>
Therefore	O
,	O
it	O
may	O
be	O
easier	O
for	O
first-time	O
autostereogram	B-Algorithm
viewers	O
to	O
"	O
see	O
"	O
their	O
first	O
3D	B-Algorithm
images	I-Algorithm
if	O
they	O
attempt	O
this	O
feat	O
with	O
bright	O
lighting	O
.	O
</s>
<s>
Vergence	B-Algorithm
control	O
is	O
important	O
in	O
being	O
able	O
to	O
see	O
3D	B-Algorithm
images	I-Algorithm
.	O
</s>
<s>
For	O
a	O
first-time	O
viewer	O
,	O
therefore	O
,	O
it	O
may	O
be	O
easier	O
to	O
see	O
the	O
autostereogram	B-Algorithm
,	O
if	O
the	O
two	O
eyes	O
rehearse	O
the	O
convergence	O
exercise	O
on	O
an	O
autostereogram	B-Algorithm
where	O
the	O
depth	O
of	O
patterns	O
across	O
a	O
particular	O
row	O
remains	O
constant	O
.	O
</s>
<s>
In	O
a	O
random	O
dot	O
autostereogram	B-Algorithm
,	O
the	O
3D	B-Algorithm
image	I-Algorithm
is	O
usually	O
shown	O
in	O
the	O
middle	O
of	O
the	O
autostereogram	B-Algorithm
against	O
a	O
background	O
depth	O
plane	O
(	O
see	O
the	O
shark	O
autostereogram	B-Algorithm
)	O
.	O
</s>
<s>
It	O
may	O
help	O
to	O
establish	O
proper	O
convergence	O
first	O
by	O
staring	O
at	O
either	O
the	O
top	O
or	O
the	O
bottom	O
of	O
the	O
autostereogram	B-Algorithm
,	O
where	O
patterns	O
are	O
usually	O
repeated	O
at	O
a	O
constant	O
interval	O
.	O
</s>
<s>
The	O
majority	O
of	O
autostereograms	B-Algorithm
,	O
including	O
those	O
in	O
this	O
article	O
,	O
are	O
designed	O
for	O
divergent	O
(	O
wall-eyed	O
)	O
viewing	O
.	O
</s>
<s>
Those	O
who	O
wear	O
eyeglasses	O
with	O
so-called	O
"	O
progressive	O
"	O
lenses	O
,	O
in	O
which	O
the	O
focal	O
length	O
gradually	O
changes	O
so	O
as	O
to	O
ease	O
the	O
viewing	O
of	O
close	O
objects	O
using	O
the	O
lower	O
part	O
of	O
the	O
lens	O
,	O
may	O
find	O
that	O
viewing	O
a	O
stereogram	B-Algorithm
is	O
easier	O
if	O
the	O
glasses	O
are	O
pushed	O
up	O
a	O
little	O
so	O
that	O
the	O
stereogram	B-Algorithm
is	O
viewed	O
through	O
a	O
part	O
of	O
the	O
lens	O
optimized	O
for	O
images	O
that	O
are	O
closer	O
than	O
the	O
actual	O
distance	O
to	O
the	O
stereogram	B-Algorithm
.	O
</s>
<s>
When	O
the	O
eyes	O
are	O
made	O
divergent	O
by	O
looking	O
(	O
or	O
pretending	O
to	O
look	O
)	O
at	O
a	O
far-away	O
object	O
,	O
the	O
overcorrection	O
from	O
viewing	O
the	O
stereogram	B-Algorithm
through	O
the	O
"	O
wrong	O
"	O
part	O
of	O
the	O
lens	O
can	O
bring	O
the	O
stereogram	B-Algorithm
into	O
focus	O
without	O
needing	O
to	O
overcome	O
the	O
tendency	O
to	O
focus	O
on	O
the	O
far-away	O
object	O
while	O
attempting	O
to	O
focus	O
on	O
the	O
stereogram	B-Algorithm
.	O
</s>
<s>
For	O
crossed-eyed	O
autostereograms	B-Algorithm
,	O
a	O
different	O
approach	O
needs	O
to	O
be	O
taken	O
.	O
</s>
<s>
Stereoblindness	B-Algorithm
,	O
however	O
,	O
is	O
not	O
known	O
to	O
permit	O
the	O
usages	O
of	O
any	O
of	O
these	O
techniques	O
,	O
especially	O
for	O
persons	O
in	O
whom	O
it	O
may	O
be	O
,	O
or	O
is	O
,	O
permanent	O
.	O
</s>
<s>
Stereogram	B-Algorithm
was	O
originally	O
used	O
to	O
describe	O
as	O
a	O
pair	O
of	O
2D	O
images	O
used	O
in	O
stereoscope	B-Algorithm
to	O
present	O
a	O
3D	B-Algorithm
image	I-Algorithm
to	O
viewers	O
.	O
</s>
<s>
The	O
"	O
auto	O
"	O
in	O
autostereogram	B-Algorithm
describes	O
an	O
image	O
that	O
does	O
not	O
require	O
a	O
stereoscope	B-Algorithm
.	O
</s>
<s>
The	O
term	O
stereogram	B-Algorithm
is	O
now	O
often	O
used	O
interchangeably	O
with	O
autostereogram	B-Algorithm
.	O
</s>
<s>
Dr.	O
Christopher	O
Tyler	O
,	O
inventor	O
of	O
the	O
autostereogram	B-Algorithm
,	O
consistently	O
refers	O
to	O
single	B-Algorithm
image	I-Algorithm
stereograms	I-Algorithm
as	O
autostereograms	B-Algorithm
to	O
distinguish	O
them	O
from	O
other	O
forms	O
of	O
stereograms	B-Algorithm
.	O
</s>
<s>
Random	B-Algorithm
dot	I-Algorithm
stereogram	I-Algorithm
,	O
describes	O
a	O
pair	O
of	O
2D	O
images	O
containing	O
random	O
dots	O
which	O
,	O
when	O
viewed	O
with	O
a	O
stereoscope	B-Algorithm
,	O
produced	O
a	O
3D	B-Algorithm
image	I-Algorithm
.	O
</s>
<s>
The	O
term	O
is	O
now	O
often	O
used	O
interchangeably	O
with	O
random	O
dot	O
autostereogram	B-Algorithm
.	O
</s>
<s>
Single	B-Algorithm
image	I-Algorithm
stereogram	I-Algorithm
(	O
SIS	O
)	O
.	O
</s>
<s>
SIS	O
differs	O
from	O
earlier	O
stereograms	B-Algorithm
in	O
its	O
use	O
of	O
a	O
single	O
2D	O
image	O
instead	O
of	O
a	O
stereo	O
pair	O
and	O
is	O
viewed	O
without	O
a	O
device	O
.	O
</s>
<s>
Thus	O
,	O
the	O
term	O
is	O
often	O
used	O
as	O
a	O
synonym	O
of	O
autostereogram	B-Algorithm
.	O
</s>
<s>
When	O
the	O
single	O
2D	O
image	O
is	O
viewed	O
with	O
proper	O
eye	O
convergence	O
,	O
it	O
causes	O
the	O
brain	O
to	O
fuse	O
different	O
patterns	O
perceived	O
by	O
the	O
two	O
eyes	O
into	O
a	O
virtual	O
3D	B-Algorithm
image	I-Algorithm
without	O
,	O
hidden	O
within	O
the	O
2D	O
image	O
,	O
the	O
aid	O
of	O
any	O
optical	O
equipment	O
.	O
</s>
<s>
Programs	O
for	O
their	O
creation	O
include	O
Mathematica	B-Language
.	O
</s>
<s>
Is	O
also	O
known	O
as	O
single	O
image	O
random	B-Algorithm
dot	I-Algorithm
stereogram	I-Algorithm
(	O
SIRDS	B-Algorithm
)	O
.	O
</s>
<s>
This	O
term	O
also	O
refers	O
to	O
autostereograms	B-Algorithm
where	O
the	O
hidden	O
3D	B-Algorithm
image	I-Algorithm
is	O
created	O
using	O
a	O
random	O
pattern	O
of	O
dots	O
within	O
one	O
image	O
,	O
shaped	O
by	O
a	O
depth	O
map	O
within	O
a	O
dedicated	O
stereogram	B-Algorithm
rendering	O
program	O
.	O
</s>
<s>
Wallpaper	B-Algorithm
autostereogram	I-Algorithm
is	O
a	O
single	O
2D	O
image	O
where	O
recognizable	O
patterns	O
are	O
repeated	O
at	O
various	O
intervals	O
to	O
raise	O
or	O
lower	O
each	O
pattern	O
's	O
perceived	O
3D	O
location	O
in	O
relation	O
to	O
the	O
display	O
surface	O
.	O
</s>
<s>
Despite	O
the	O
repetition	O
,	O
these	O
are	O
a	O
type	O
of	O
single	O
image	O
autostereogram	B-Algorithm
.	O
</s>
<s>
A	O
single	O
image	O
random	O
text	O
ASCII	B-Algorithm
stereogram	I-Algorithm
is	O
an	O
alternative	O
to	O
SIRDS	B-Algorithm
using	O
random	O
ASCII	B-Protocol
text	I-Protocol
instead	O
of	O
dots	O
to	O
produce	O
a	O
3D	O
form	O
of	O
ASCII	B-Protocol
art	O
.	O
</s>
<s>
In	O
a	O
map	B-Algorithm
textured	I-Algorithm
stereogram	I-Algorithm
,	O
"	O
a	O
fitted	O
texture	O
is	O
mapped	O
onto	O
the	O
depth	O
image	O
and	O
repeated	O
a	O
number	O
of	O
times	O
"	O
resulting	O
in	O
a	O
pattern	O
where	O
the	O
resulting	O
3D	B-Algorithm
image	I-Algorithm
is	O
often	O
partially	O
or	O
fully	O
visible	O
before	O
viewing	O
.	O
</s>
