<s>
Part-based	B-General_Concept
models	I-General_Concept
refers	O
to	O
a	O
broad	O
class	O
of	O
detection	O
algorithms	O
used	O
on	O
images	O
,	O
in	O
which	O
various	O
parts	O
of	O
the	O
image	O
are	O
used	O
separately	O
in	O
order	O
to	O
determine	O
if	O
and	O
where	O
an	O
object	O
of	O
interest	O
exists	O
.	O
</s>
<s>
Amongst	O
these	O
methods	O
a	O
very	O
popular	O
one	O
is	O
the	O
constellation	B-General_Concept
model	I-General_Concept
which	O
refers	O
to	O
those	O
schemes	O
which	O
seek	O
to	O
detect	O
a	O
small	O
number	O
of	O
features	O
and	O
their	O
relative	O
positions	O
to	O
then	O
determine	O
whether	O
or	O
not	O
the	O
object	O
of	O
interest	O
is	O
present	O
.	O
</s>
<s>
These	O
models	O
will	O
be	O
covered	O
in	O
the	O
constellation	B-General_Concept
models	I-General_Concept
section	O
.	O
</s>
<s>
To	O
get	O
a	O
better	O
idea	O
of	O
what	O
is	O
meant	O
by	O
constellation	B-General_Concept
model	I-General_Concept
an	O
example	O
may	O
be	O
more	O
illustrative	O
.	O
</s>
<s>
Say	O
we	O
are	O
trying	O
to	O
detect	B-General_Concept
faces	I-General_Concept
.	O
</s>
<s>
A	O
constellation	B-General_Concept
model	I-General_Concept
would	O
use	O
smaller	O
part	O
detectors	O
,	O
for	O
instance	O
mouth	O
,	O
nose	O
and	O
eye	O
detectors	O
and	O
make	O
a	O
judgment	O
about	O
whether	O
an	O
image	O
has	O
a	O
face	O
based	O
on	O
the	O
relative	O
positions	O
in	O
which	O
the	O
components	O
fire	O
.	O
</s>
<s>
Many	O
overlapping	O
ideas	O
are	O
included	O
under	O
the	O
title	O
part-based	B-General_Concept
models	I-General_Concept
even	O
after	O
having	O
excluded	O
those	O
models	O
of	O
the	O
constellation	O
variety	O
.	O
</s>
<s>
The	O
algorithm	O
is	O
effective	O
because	O
it	O
imposes	O
much	O
less	O
constellational	O
rigidity	O
the	O
way	O
the	O
constellation	B-General_Concept
model	I-General_Concept
does	O
.	O
</s>
<s>
Admittedly	O
the	O
constellation	B-General_Concept
model	I-General_Concept
can	O
be	O
modified	O
to	O
allow	O
for	O
occlusions	O
and	O
other	O
large	O
abnormalities	O
but	O
this	O
model	O
is	O
naturally	O
suited	O
to	O
it	O
.	O
</s>
