<s>
In	O
computer	B-Application
vision	I-Application
and	O
computer	O
graphics	O
,	O
3D	B-Algorithm
reconstruction	I-Algorithm
is	O
the	O
process	O
of	O
capturing	O
the	O
shape	O
and	O
appearance	O
of	O
real	O
objects	O
.	O
</s>
<s>
If	O
the	O
model	O
is	O
allowed	O
to	O
change	O
its	O
shape	O
in	O
time	O
,	O
this	O
is	O
referred	O
to	O
as	O
non-rigid	B-Algorithm
or	I-Algorithm
spatio-temporal	I-Algorithm
reconstruction	O
.	O
</s>
<s>
The	O
research	O
of	O
3D	B-Algorithm
reconstruction	I-Algorithm
has	O
always	O
been	O
a	O
difficult	O
goal	O
.	O
</s>
<s>
By	O
Using	O
3D	B-Algorithm
reconstruction	I-Algorithm
one	O
can	O
determine	O
any	O
object	O
's	O
3D	O
profile	O
,	O
as	O
well	O
as	O
knowing	O
the	O
3D	O
coordinate	O
of	O
any	O
point	O
on	O
the	O
profile	O
.	O
</s>
<s>
The	O
3D	B-Algorithm
reconstruction	I-Algorithm
of	O
objects	O
is	O
a	O
generally	O
scientific	O
problem	O
and	O
core	O
technology	O
of	O
a	O
wide	O
variety	O
of	O
fields	O
,	O
such	O
as	O
Computer	B-Application
Aided	I-Application
Geometric	I-Application
Design	I-Application
(	O
CAGD	B-Application
)	O
,	O
computer	O
graphics	O
,	O
computer	O
animation	O
,	O
computer	B-Application
vision	I-Application
,	O
medical	B-Application
imaging	I-Application
,	O
computational	O
science	O
,	O
virtual	B-Application
reality	I-Application
,	O
digital	O
media	O
,	O
etc	O
.	O
</s>
<s>
Digital	B-Application
elevation	I-Application
models	I-Application
can	O
be	O
reconstructed	O
using	O
methods	O
such	O
as	O
airborne	O
laser	O
altimetry	O
or	O
synthetic	B-Application
aperture	I-Application
radar	I-Application
.	O
</s>
<s>
range	O
data	O
methods	O
,	O
given	O
the	O
depth	O
map	O
,	O
reconstruct	O
the	O
3D	O
profile	O
by	O
numerical	B-General_Concept
approximation	I-General_Concept
approach	O
and	O
build	O
the	O
object	O
in	O
scenario	O
based	O
on	O
model	O
.	O
</s>
<s>
These	O
methods	O
actively	O
interfere	O
with	O
the	O
reconstructed	O
object	O
,	O
either	O
mechanically	O
or	O
radiometrically	O
using	O
rangefinders	B-Algorithm
,	O
in	O
order	O
to	O
acquire	O
the	O
depth	O
map	O
,	O
e.g.	O
</s>
<s>
structured	B-Algorithm
light	I-Algorithm
,	O
laser	O
range	O
finder	O
and	O
other	O
active	O
sensing	O
techniques	O
.	O
</s>
<s>
More	O
applicable	O
radiometric	O
methods	O
emit	O
radiance	B-Application
towards	O
the	O
object	O
and	O
then	O
measure	O
its	O
reflected	O
part	O
.	O
</s>
<s>
Examples	O
range	O
from	O
moving	O
light	O
sources	O
,	O
colored	O
visible	O
light	O
,	O
time-of-flight	B-Device
lasers	O
to	O
microwaves	O
or	O
3D	B-Algorithm
ultrasound	I-Algorithm
.	O
</s>
<s>
See	O
3D	B-Algorithm
scanning	I-Algorithm
for	O
more	O
details	O
.	O
</s>
<s>
Passive	O
methods	O
of	O
3D	B-Algorithm
reconstruction	I-Algorithm
do	O
not	O
interfere	O
with	O
the	O
reconstructed	O
object	O
;	O
they	O
only	O
use	O
a	O
sensor	O
to	O
measure	O
the	O
radiance	B-Application
reflected	O
or	O
emitted	O
by	O
the	O
object	O
's	O
surface	O
to	O
infer	O
its	O
3D	O
structure	O
through	O
image	B-Application
understanding	I-Application
.	O
</s>
<s>
Typically	O
,	O
the	O
sensor	O
is	O
an	O
image	O
sensor	O
in	O
a	O
camera	O
sensitive	O
to	O
visible	O
light	O
and	O
the	O
input	O
to	O
the	O
method	O
is	O
a	O
set	O
of	O
digital	B-Algorithm
images	I-Algorithm
(	O
one	O
,	O
two	O
or	O
more	O
)	O
or	O
video	O
.	O
</s>
<s>
Silhouettes	O
,	O
shading	B-General_Concept
and	O
texture	O
)	O
to	O
measure	O
3D	O
shape	O
,	O
and	O
that	O
's	O
why	O
it	O
is	O
also	O
named	O
Shape-From-X	O
,	O
where	O
X	O
can	O
be	O
silhouettes	O
,	O
shading	B-General_Concept
,	O
texture	O
etc	O
.	O
</s>
<s>
3D	B-Algorithm
reconstruction	I-Algorithm
through	O
monocular	O
cues	O
is	O
simple	O
and	O
quick	O
,	O
and	O
only	O
one	O
appropriate	O
digital	B-Algorithm
image	I-Algorithm
is	O
needed	O
thus	O
only	O
one	O
camera	O
is	O
adequate	O
.	O
</s>
<s>
Technically	O
,	O
it	O
avoids	O
stereo	B-Algorithm
correspondence	I-Algorithm
,	O
which	O
is	O
fairly	O
complex	O
.	O
</s>
<s>
Shape-from-shading	O
Due	O
to	O
the	O
analysis	O
of	O
the	O
shade	O
information	O
in	O
the	O
image	O
,	O
by	O
using	O
Lambertian	O
reflectance	O
,	O
the	O
depth	O
of	O
normal	O
information	O
of	O
the	O
object	O
surface	O
is	O
restored	O
to	O
reconstruct	O
.	O
</s>
<s>
Photometric	B-Algorithm
Stereo	I-Algorithm
This	O
approach	O
is	O
more	O
sophisticated	O
than	O
the	O
shape-of-shading	O
method	O
.	O
</s>
<s>
Shape-from-texture	O
Suppose	O
such	O
an	O
object	O
with	O
smooth	O
surface	O
covered	O
by	O
replicated	O
texture	O
units	O
,	O
and	O
its	O
projection	O
from	O
3D	O
to	O
2D	O
causes	O
distortion	O
and	O
perspective	B-Application
.	O
</s>
<s>
Distortion	O
and	O
perspective	B-Application
measured	O
in	O
2D	O
images	O
provide	O
the	O
hint	O
for	O
inversely	O
solving	O
depth	O
of	O
normal	O
information	O
of	O
the	O
object	O
surface	O
.	O
</s>
<s>
Stereo	B-Algorithm
vision	I-Algorithm
obtains	O
the	O
3-dimensional	O
geometric	O
information	O
of	O
an	O
object	O
from	O
multiple	O
images	O
based	O
on	O
the	O
research	O
of	O
human	O
visual	O
system	O
.	O
</s>
<s>
Images	O
of	O
an	O
object	O
acquired	O
by	O
two	O
cameras	O
simultaneously	O
in	O
different	O
viewing	B-General_Concept
angles	I-General_Concept
,	O
or	O
by	O
one	O
single	O
camera	O
at	O
different	O
time	O
in	O
different	O
viewing	B-General_Concept
angles	I-General_Concept
,	O
are	O
used	O
to	O
restore	O
its	O
3D	O
geometric	O
information	O
and	O
reconstruct	O
its	O
3D	O
profile	O
and	O
location	O
.	O
</s>
<s>
This	O
is	O
more	O
direct	O
than	O
Monocular	O
methods	O
such	O
as	O
shape-from-shading	O
.	O
</s>
<s>
Binocular	O
stereo	B-Algorithm
vision	I-Algorithm
method	O
requires	O
two	O
identical	O
cameras	O
with	O
parallel	O
optical	O
axis	O
to	O
observe	O
one	O
same	O
object	O
,	O
acquiring	O
two	O
images	O
from	O
different	O
points	O
of	O
view	O
.	O
</s>
<s>
Binocular	O
stereo	B-Algorithm
vision	I-Algorithm
method	O
is	O
well	O
developed	O
and	O
stably	O
contributes	O
to	O
favorable	O
3D	B-Algorithm
reconstruction	I-Algorithm
,	O
leading	O
to	O
a	O
better	O
performance	O
when	O
compared	O
to	O
other	O
3D	O
construction	O
.	O
</s>
<s>
The	O
approach	O
of	O
using	O
Binocular	O
stereo	B-Algorithm
vision	I-Algorithm
to	O
acquire	O
object	O
's	O
3D	O
geometric	O
information	O
is	O
on	O
the	O
basis	O
of	O
visual	O
disparity	O
.	O
</s>
<s>
The	O
following	O
picture	O
provides	O
a	O
simple	O
schematic	O
diagram	O
of	O
horizontally	O
sighted	O
Binocular	O
Stereo	B-Algorithm
Vision	I-Algorithm
,	O
where	O
b	O
is	O
the	O
baseline	O
between	O
projective	O
centers	O
of	O
two	O
cameras	O
.	O
</s>
<s>
where	O
are	O
coordinates	O
of	O
in	O
the	O
left	O
camera	O
's	O
coordinate	O
system	O
,	O
is	O
focal	B-Algorithm
length	I-Algorithm
of	O
the	O
camera	O
.	O
</s>
<s>
The	O
3D	B-Algorithm
reconstruction	I-Algorithm
consists	O
of	O
the	O
following	O
sections	O
:	O
</s>
<s>
2D	O
digital	B-Algorithm
image	I-Algorithm
acquisition	O
is	O
the	O
information	O
source	O
of	O
3D	B-Algorithm
reconstruction	I-Algorithm
.	O
</s>
<s>
Commonly	O
used	O
3D	B-Algorithm
reconstruction	I-Algorithm
is	O
based	O
on	O
two	O
or	O
more	O
images	O
,	O
although	O
it	O
may	O
employ	O
only	O
one	O
image	O
in	O
some	O
cases	O
.	O
</s>
<s>
Camera	O
calibration	O
in	O
Binocular	O
Stereo	B-Algorithm
Vision	I-Algorithm
refers	O
to	O
the	O
determination	O
of	O
the	O
mapping	O
relationship	O
between	O
the	O
image	O
points	O
and	O
,	O
and	O
space	O
coordinate	O
in	O
the	O
3D	O
scenario	O
.	O
</s>
<s>
Camera	O
calibration	O
is	O
a	O
basic	O
and	O
essential	O
part	O
in	O
3D	B-Algorithm
reconstruction	I-Algorithm
via	O
Binocular	O
Stereo	B-Algorithm
Vision	I-Algorithm
.	O
</s>
<s>
The	O
aim	O
of	O
feature	O
extraction	O
is	O
to	O
gain	O
the	O
characteristics	O
of	O
the	O
images	O
,	O
through	O
which	O
the	O
stereo	B-Algorithm
correspondence	I-Algorithm
processes	O
.	O
</s>
<s>
There	O
is	O
no	O
such	O
universally	O
applicable	O
theory	O
for	O
features	O
extraction	O
,	O
leading	O
to	O
a	O
great	O
diversity	O
of	O
stereo	B-Algorithm
correspondence	I-Algorithm
in	O
Binocular	O
Stereo	B-Algorithm
Vision	I-Algorithm
research	O
.	O
</s>
<s>
Stereo	B-Algorithm
correspondence	I-Algorithm
is	O
to	O
establish	O
the	O
correspondence	O
between	O
primitive	O
factors	O
in	O
images	O
,	O
i.e.	O
</s>
<s>
Due	O
to	O
the	O
fact	O
that	O
accuracy	O
of	O
3D	B-Algorithm
reconstruction	I-Algorithm
depends	O
on	O
the	O
precision	O
of	O
correspondence	O
,	O
error	O
of	O
camera	O
location	O
parameters	O
and	O
so	O
on	O
,	O
the	O
previous	O
procedures	O
must	O
be	O
done	O
carefully	O
to	O
achieve	O
relatively	O
accurate	O
3D	B-Algorithm
reconstruction	I-Algorithm
.	O
</s>
<s>
3D	B-Algorithm
reconstruction	I-Algorithm
has	O
applications	O
in	O
many	O
fields	O
.	O
</s>
<s>
Mostly	O
algorithms	O
available	O
for	O
3D	B-Algorithm
reconstruction	I-Algorithm
are	O
extremely	O
slow	O
and	O
cannot	O
be	O
used	O
in	O
real-time	O
.	O
</s>
<s>
An	O
algorithm	O
called	O
marching	B-Algorithm
cubes	I-Algorithm
established	O
the	O
use	O
of	O
such	O
methods	O
.	O
</s>
<s>
There	O
are	O
several	O
studies	O
related	O
to	O
post-processing	O
techniques	O
used	O
in	O
the	O
reconstruction	O
for	O
the	O
detection	B-Algorithm
and	I-Algorithm
refinement	I-Algorithm
of	I-Algorithm
corners	I-Algorithm
but	O
these	O
methods	O
increase	O
the	O
complexity	O
of	O
the	O
solution	O
.	O
</s>
<s>
Along	O
each	O
ray	O
,	O
opacity	O
and	O
color	O
need	O
to	O
be	O
calculated	O
at	O
every	O
voxel	B-Algorithm
.	O
</s>
<s>
Some	O
usual	O
methods	O
in	O
medical	B-Application
image	I-Application
are	O
MIP	B-Application
(	O
maximum	B-Application
intensity	I-Application
projection	I-Application
)	O
,	O
MinIP	O
(	O
minimum	O
intensity	O
projection	O
)	O
,	O
AC	O
(	O
alpha	B-Algorithm
compositing	I-Algorithm
)	O
and	O
NPVR	O
(	O
non-photorealistic	O
volume	O
rendering	O
)	O
.	O
</s>
<s>
In	O
this	O
filtering	O
technique	O
input	O
space	O
is	O
sampled	O
using	O
a	O
grid	O
of	O
3D	O
voxels	B-Algorithm
to	O
reduce	O
the	O
number	O
of	O
points	O
.	O
</s>
<s>
For	O
each	O
voxel	B-Algorithm
,	O
a	O
centroid	O
is	O
chosen	O
as	O
the	O
representative	O
of	O
all	O
points	O
.	O
</s>
<s>
There	O
are	O
two	O
approaches	O
,	O
the	O
selection	O
of	O
the	O
voxel	B-Algorithm
centroid	O
or	O
select	O
the	O
centroid	O
of	O
the	O
points	O
lying	O
within	O
the	O
voxel	B-Algorithm
.	O
</s>
<s>
The	O
Voxel	B-Algorithm
Grid	O
method	O
presents	O
the	O
same	O
problems	O
as	O
other	O
filtering	O
techniques	O
:	O
impossibility	O
of	O
defining	O
the	O
final	O
number	O
of	O
points	O
that	O
represent	O
the	O
surface	O
,	O
geometric	O
information	O
loss	O
due	O
to	O
the	O
reduction	O
of	O
the	O
points	O
inside	O
a	O
voxel	B-Algorithm
and	O
sensitivity	O
to	O
noisy	O
input	O
spaces	O
.	O
</s>
