<s>
Foreground	O
detection	O
is	O
one	O
of	O
the	O
major	O
tasks	O
in	O
the	O
field	O
of	O
computer	B-General_Concept
vision	I-General_Concept
and	O
image	B-Algorithm
processing	I-Algorithm
whose	O
aim	O
is	O
to	O
detect	O
changes	O
in	O
image	O
sequences	O
.	O
</s>
<s>
Background	B-Algorithm
subtraction	I-Algorithm
is	O
any	O
technique	O
which	O
allows	O
an	O
image	O
's	O
foreground	O
to	O
be	O
extracted	O
for	O
further	O
processing	O
(	O
object	O
recognition	O
etc	O
.	O
</s>
<s>
Many	O
applications	O
do	O
not	O
need	O
to	O
know	O
everything	O
about	O
the	O
evolution	O
of	O
movement	O
in	O
a	O
video	O
sequence	O
,	O
but	O
only	O
require	O
the	O
information	O
of	O
changes	O
in	O
the	O
scene	O
,	O
because	O
an	O
image	O
's	O
regions	B-Algorithm
of	I-Algorithm
interest	I-Algorithm
are	O
objects	O
(	O
humans	O
,	O
cars	O
,	O
text	O
etc	O
.	O
)	O
</s>
<s>
Background	B-Algorithm
subtraction	I-Algorithm
is	O
a	O
widely	O
used	O
approach	O
for	O
detecting	B-Algorithm
moving	I-Algorithm
objects	I-Algorithm
in	O
videos	O
from	O
static	O
cameras	O
.	O
</s>
<s>
Background	B-Algorithm
subtraction	I-Algorithm
is	O
mostly	O
done	O
if	O
the	O
image	O
in	O
question	O
is	O
a	O
part	O
of	O
a	O
video	O
stream	O
.	O
</s>
<s>
Background	B-Algorithm
subtraction	I-Algorithm
provides	O
important	O
cues	O
for	O
numerous	O
applications	O
in	O
computer	B-General_Concept
vision	I-General_Concept
,	O
for	O
example	O
surveillance	O
tracking	B-Operating_System
or	O
human	B-General_Concept
pose	I-General_Concept
estimation	I-General_Concept
.	O
</s>
<s>
Background	B-Algorithm
subtraction	I-Algorithm
is	O
generally	O
based	O
on	O
a	O
static	O
background	O
hypothesis	O
which	O
is	O
often	O
not	O
applicable	O
in	O
real	O
environments	O
.	O
</s>
<s>
A	O
robust	O
background	B-Algorithm
subtraction	I-Algorithm
algorithm	O
should	O
be	O
able	O
to	O
handle	O
lighting	O
changes	O
,	O
repetitive	O
motions	O
from	O
clutter	O
and	O
long-term	O
scene	O
changes	O
.	O
</s>
<s>
A	O
threshold	O
"	O
Threshold	O
"	O
is	O
put	O
on	O
this	O
difference	O
image	O
to	O
improve	O
the	O
subtraction	O
(	O
see	O
Image	O
thresholding	B-Algorithm
)	O
.	O
</s>
<s>
Foreground	O
pixels	O
are	O
grouped	O
using	O
2D	O
connected	B-General_Concept
component	I-General_Concept
analysis	I-General_Concept
.	O
</s>
<s>
An	O
on-line	O
K-means	B-Algorithm
approximation	O
is	O
used	O
to	O
update	O
the	O
Gaussians	O
.	O
</s>
