<s>
In	O
image	B-General_Concept
analysis	I-General_Concept
,	O
the	O
average	B-Algorithm
with	I-Algorithm
limited	I-Algorithm
data	I-Algorithm
validity	I-Algorithm
is	O
an	O
image	O
filter	O
for	O
feature-preserving	O
noise	B-Algorithm
removal	O
,	O
consisting	O
in	O
a	O
smoothing	O
filter	O
that	O
only	O
involves	O
pixels	O
satisfying	O
some	O
validity	O
criterion	O
.	O
</s>
<s>
If	O
some	O
feature	O
of	O
noise	B-Algorithm
elements	O
is	O
known	O
,	O
it	O
is	O
possible	O
to	O
use	O
it	O
to	O
define	O
a	O
criterion	O
to	O
detect	O
invalid	O
pixels	O
,	O
and	O
selectively	O
smooth	O
only	O
invalid	O
pixels	O
using	O
data	O
coming	O
only	O
from	O
valid	O
pixels	O
,	O
thus	O
avoiding	O
to	O
affect	O
other	O
features	O
of	O
the	O
image	O
.	O
</s>
<s>
This	O
approach	O
gives	O
an	O
edge-preserving	B-Algorithm
smoothing	I-Algorithm
.	O
</s>
