<s>
Salt-and-pepper	B-Algorithm
noise	I-Algorithm
,	O
also	O
known	O
as	O
impulse	O
noise	B-Algorithm
,	O
is	O
a	O
form	O
of	O
noise	B-Algorithm
sometimes	O
seen	O
on	O
digital	B-Algorithm
images	I-Algorithm
.	O
</s>
<s>
This	O
noise	B-Algorithm
can	O
be	O
caused	O
by	O
sharp	O
and	O
sudden	O
disturbances	O
in	O
the	O
image	O
signal	O
.	O
</s>
<s>
It	O
presents	O
itself	O
as	O
sparsely	O
occurring	O
white	O
and	O
black	O
pixels	B-Algorithm
.	O
</s>
<s>
An	O
effective	O
noise	B-Algorithm
reduction	O
method	O
for	O
this	O
type	O
of	O
noise	B-Algorithm
is	O
a	O
median	B-Algorithm
filter	I-Algorithm
or	O
a	O
morphological	B-Algorithm
filter	I-Algorithm
.	O
</s>
<s>
For	O
reducing	O
either	O
salt	B-Algorithm
noise	I-Algorithm
or	O
pepper	B-Algorithm
noise	I-Algorithm
,	O
but	O
not	O
both	O
,	O
a	O
contraharmonic	O
mean	O
filter	O
can	O
be	O
effective	O
.	O
</s>
