<s>
Computer	B-Algorithm
stereo	I-Algorithm
vision	I-Algorithm
is	O
the	O
extraction	O
of	O
3D	O
information	O
from	O
digital	O
images	O
,	O
such	O
as	O
those	O
obtained	O
by	O
a	O
CCD	B-Algorithm
camera	I-Algorithm
.	O
</s>
<s>
This	O
is	O
similar	O
to	O
the	O
biological	O
process	O
of	O
stereopsis	B-Algorithm
.	O
</s>
<s>
In	O
traditional	O
stereo	B-Algorithm
vision	I-Algorithm
,	O
two	O
cameras	O
,	O
displaced	O
horizontally	O
from	O
one	O
another	O
,	O
are	O
used	O
to	O
obtain	O
two	O
differing	O
views	O
on	O
a	O
scene	O
,	O
in	O
a	O
manner	O
similar	O
to	O
human	O
binocular	B-Algorithm
vision	I-Algorithm
.	O
</s>
<s>
By	O
comparing	O
these	O
two	O
images	O
,	O
the	O
relative	O
depth	O
information	O
can	O
be	O
obtained	O
in	O
the	O
form	O
of	O
a	O
disparity	O
map	O
,	O
which	O
encodes	O
the	O
difference	O
in	O
horizontal	O
coordinates	O
of	O
corresponding	B-Algorithm
image	O
points	O
.	O
</s>
<s>
The	O
values	O
in	O
this	O
disparity	O
map	O
are	O
inversely	O
proportional	O
to	O
the	O
scene	O
depth	O
at	O
the	O
corresponding	B-Algorithm
pixel	O
location	O
.	O
</s>
<s>
In	O
a	O
computer	B-Application
vision	I-Application
system	O
,	O
several	O
pre-processing	O
steps	O
are	O
required	O
.	O
</s>
<s>
This	O
ensures	O
that	O
the	O
observed	O
image	O
matches	O
the	O
projection	O
of	O
an	O
ideal	O
pinhole	B-Algorithm
camera	I-Algorithm
.	O
</s>
<s>
The	O
image	O
must	O
be	O
projected	O
back	O
to	O
a	O
common	O
plane	O
to	O
allow	O
comparison	O
of	O
the	O
image	O
pairs	O
,	O
known	O
as	O
image	B-Algorithm
rectification	I-Algorithm
.	O
</s>
<s>
Optionally	O
,	O
the	O
received	O
disparity	O
map	O
is	O
projected	O
into	O
a	O
3d	B-Algorithm
point	I-Algorithm
cloud	I-Algorithm
.	O
</s>
<s>
By	O
utilising	O
the	O
cameras	O
 '	O
projective	O
parameters	O
,	O
the	O
point	B-Algorithm
cloud	I-Algorithm
can	O
be	O
computed	O
such	O
that	O
it	O
provides	O
measurements	O
at	O
a	O
known	O
scale	O
.	O
</s>
<s>
The	O
active	O
stereo	B-Algorithm
vision	I-Algorithm
is	O
a	O
form	O
of	O
stereo	B-Algorithm
vision	I-Algorithm
which	O
actively	O
employs	O
a	O
light	O
such	O
as	O
a	O
laser	O
or	O
a	O
structured	B-General_Concept
light	I-General_Concept
to	O
simplify	O
the	O
stereo	O
matching	O
problem	O
.	O
</s>
<s>
The	O
opposed	O
term	O
is	O
passive	O
stereo	B-Algorithm
vision	I-Algorithm
.	O
</s>
<s>
The	O
conventional	O
structured-light	O
vision	O
(	O
SLV	O
)	O
employs	O
a	O
structured	B-General_Concept
light	I-General_Concept
or	O
laser	O
,	O
and	O
finds	O
projector-camera	O
correspondences	O
.	O
</s>
<s>
The	O
conventional	O
active	O
stereo	B-Algorithm
vision	I-Algorithm
(	O
ASV	O
)	O
employs	O
a	O
structured	B-General_Concept
light	I-General_Concept
or	O
laser	O
,	O
however	O
,	O
the	O
stereo	O
matching	O
is	O
performed	O
only	O
for	O
camera-camera	O
correspondences	O
,	O
in	O
the	O
same	O
way	O
as	O
the	O
passive	O
stereo	B-Algorithm
vision	I-Algorithm
.	O
</s>
<s>
3D	O
stereo	B-Algorithm
displays	I-Algorithm
find	O
many	O
applications	O
in	O
entertainment	O
,	O
information	O
transfer	O
and	O
automated	O
systems	O
.	O
</s>
<s>
Stereo	B-Algorithm
vision	I-Algorithm
is	O
highly	O
important	O
in	O
fields	O
such	O
as	O
robotics	O
to	O
extract	O
information	O
about	O
the	O
relative	O
position	O
of	O
3D	O
objects	O
in	O
the	O
vicinity	O
of	O
autonomous	O
systems	O
.	O
</s>
<s>
Scientific	O
applications	O
for	O
digital	O
stereo	B-Algorithm
vision	I-Algorithm
include	O
the	O
extraction	O
of	O
information	O
from	O
aerial	O
surveys	O
,	O
for	O
calculation	O
of	O
contour	O
maps	O
or	O
even	O
geometry	O
extraction	O
for	O
3D	O
building	O
mapping	O
,	O
photogrammetric	O
satellite	O
mapping	O
,	O
or	O
calculation	O
of	O
3D	O
heliographical	O
information	O
such	O
as	O
obtained	O
by	O
the	O
NASA	O
STEREO	O
project	O
.	O
</s>
<s>
Stereoscopic	B-Algorithm
vision	I-Algorithm
gives	O
two	O
images	O
of	O
the	O
same	O
scene	O
,	O
from	O
different	O
positions	O
.	O
</s>
<s>
In	O
the	O
adjacent	O
diagram	O
light	O
from	O
the	O
point	O
A	O
is	O
transmitted	O
through	O
the	O
entry	O
points	O
of	O
pinhole	B-Algorithm
cameras	I-Algorithm
at	O
B	O
and	O
D	O
,	O
onto	O
image	O
screens	O
at	O
E	O
and	O
H	O
.	O
</s>
<s>
These	O
formulas	O
allow	O
for	O
the	O
occlusion	B-Algorithm
of	O
voxels	B-Algorithm
,	O
seen	O
in	O
one	O
image	O
on	O
the	O
surface	O
of	O
the	O
object	O
,	O
by	O
closer	O
voxels	B-Algorithm
seen	O
in	O
the	O
other	O
image	O
,	O
on	O
the	O
surface	O
of	O
the	O
object	O
.	O
</s>
<s>
Where	O
the	O
image	O
planes	O
are	O
not	O
co-planar	O
,	O
image	B-Algorithm
rectification	I-Algorithm
is	O
required	O
to	O
adjust	O
the	O
images	O
as	O
if	O
they	O
were	O
co-planar	O
.	O
</s>
<s>
The	O
images	O
may	O
also	O
need	O
rectification	O
to	O
make	O
each	O
image	O
equivalent	O
to	O
the	O
image	O
taken	O
from	O
a	O
pinhole	B-Algorithm
camera	I-Algorithm
projecting	O
to	O
a	O
flat	O
plane	O
.	O
</s>
<s>
The	O
method	O
described	O
above	O
for	O
evaluating	O
smoothness	O
is	O
based	O
on	O
information	O
theory	O
,	O
and	O
an	O
assumption	O
that	O
the	O
influence	O
of	O
the	O
color	O
of	O
a	O
voxel	B-Algorithm
influences	O
the	O
color	O
of	O
nearby	O
voxels	B-Algorithm
according	O
to	O
the	O
normal	O
distribution	O
on	O
the	O
distance	O
between	O
points	O
.	O
</s>
<s>
The	O
least	B-Algorithm
squares	I-Algorithm
measure	O
may	O
be	O
used	O
to	O
measure	O
the	O
information	O
content	O
of	O
the	O
stereoscopic	O
images	O
,	O
given	O
depths	O
at	O
each	O
point	O
.	O
</s>
<s>
Assume	O
that	O
two	O
pixels	O
are	O
more	O
likely	O
to	O
be	O
the	O
same	O
color	O
,	O
the	O
closer	O
the	O
voxels	B-Algorithm
they	O
represent	O
are	O
.	O
</s>
<s>
The	O
total	O
measure	O
of	O
smoothness	O
uses	O
the	O
distance	O
between	O
voxels	B-Algorithm
as	O
an	O
estimate	O
of	O
the	O
expected	O
standard	O
deviation	O
of	O
the	O
color	O
difference	O
,	O
</s>
<s>
However	O
methods	O
exist	O
for	O
computers	O
based	O
on	O
heuristics	B-Algorithm
that	O
approximate	O
the	O
result	O
in	O
a	O
reasonable	O
amount	O
of	O
time	O
.	O
</s>
<s>
Also	O
methods	O
exist	O
based	O
on	O
neural	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
Efficient	O
implementation	O
of	O
stereoscopic	B-Algorithm
vision	I-Algorithm
is	O
an	O
area	O
of	O
active	O
research	O
.	O
</s>
