<s>
Color	B-Algorithm
moments	I-Algorithm
are	O
measures	O
that	O
characterise	O
color	O
distribution	O
in	O
an	O
image	O
in	O
the	O
same	O
way	O
that	O
central	B-General_Concept
moments	I-General_Concept
uniquely	O
describe	O
a	O
probability	O
distribution	O
.	O
</s>
<s>
Color	B-Algorithm
moments	I-Algorithm
are	O
mainly	O
used	O
for	O
color	O
indexing	O
purposes	O
as	O
features	O
in	O
image	B-General_Concept
retrieval	I-General_Concept
applications	O
in	O
order	O
to	O
compare	O
how	O
similar	O
two	O
images	O
are	O
based	O
on	O
color	O
.	O
</s>
<s>
Usually	O
one	O
image	O
is	O
compared	O
to	O
a	O
database	O
of	O
digital	B-Algorithm
images	I-Algorithm
with	O
pre-computed	O
features	O
in	O
order	O
to	O
find	O
and	O
retrieve	O
a	O
similar	O
Image	O
.	O
</s>
<s>
Color	B-Algorithm
moments	I-Algorithm
are	O
scaling	O
and	O
rotation	O
invariant	O
.	O
</s>
<s>
It	O
is	O
usually	O
the	O
case	O
that	O
only	O
the	O
first	O
three	O
color	B-Algorithm
moments	I-Algorithm
are	O
used	O
as	O
features	O
in	O
image	B-General_Concept
retrieval	I-General_Concept
applications	O
as	O
most	O
of	O
the	O
color	O
distribution	O
information	O
is	O
contained	O
in	O
the	O
low-order	O
moments	O
.	O
</s>
<s>
Since	O
color	B-Algorithm
moments	I-Algorithm
encode	O
both	O
shape	O
and	O
color	O
information	O
they	O
are	O
a	O
good	O
feature	O
to	O
use	O
under	O
changing	O
lighting	O
conditions	O
,	O
but	O
they	O
cannot	O
handle	O
occlusion	O
very	O
successfully	O
.	O
</s>
<s>
Color	B-Algorithm
moments	I-Algorithm
can	O
be	O
computed	O
for	O
any	O
color	O
model	O
.	O
</s>
<s>
Three	O
color	B-Algorithm
moments	I-Algorithm
are	O
computed	O
per	O
channel	O
(	O
e.g.	O
</s>
<s>
Computing	O
color	B-Algorithm
moments	I-Algorithm
is	O
done	O
in	O
the	O
same	O
way	O
as	O
computing	O
moments	O
of	O
a	O
probability	O
distribution	O
.	O
</s>
<s>
The	O
second	O
color	O
moment	O
is	O
the	O
standard	B-General_Concept
deviation	I-General_Concept
,	O
which	O
is	O
obtained	O
by	O
taking	O
the	O
square	O
root	O
of	O
the	O
variance	O
of	O
the	O
color	O
distribution	O
.	O
</s>
<s>
The	O
third	O
color	O
moment	O
is	O
the	O
skewness	B-General_Concept
.	O
</s>
<s>
Skewness	B-General_Concept
can	O
be	O
computed	O
with	O
the	O
following	O
formula	O
:	O
</s>
<s>
Kurtosis	O
is	O
the	O
fourth	O
color	O
moment	O
,	O
and	O
,	O
similarly	O
to	O
skewness	B-General_Concept
,	O
it	O
provides	O
information	O
about	O
the	O
shape	O
of	O
the	O
color	O
distribution	O
.	O
</s>
<s>
Higher-order	O
color	B-Algorithm
moments	I-Algorithm
are	O
usually	O
not	O
part	O
of	O
the	O
color	B-Algorithm
moments	I-Algorithm
feature	O
set	O
in	O
image	B-General_Concept
retrieval	I-General_Concept
tasks	O
as	O
they	O
require	O
more	O
data	O
in	O
order	O
to	O
obtain	O
a	O
good	O
estimate	O
of	O
their	O
value	O
,	O
and	O
also	O
the	O
lower-order	O
moments	O
generally	O
provide	O
enough	O
information	O
.	O
</s>
<s>
Color	B-Algorithm
moments	I-Algorithm
have	O
significant	O
applications	O
in	O
image	B-General_Concept
retrieval	I-General_Concept
.	O
</s>
<s>
The	O
greatest	O
advantage	O
of	O
using	O
color	B-Algorithm
moments	I-Algorithm
comes	O
from	O
the	O
fact	O
that	O
there	O
is	O
no	O
need	O
to	O
store	O
the	O
complete	O
color	O
distribution	O
.	O
</s>
<s>
This	O
greatly	O
speeds	O
up	O
image	B-General_Concept
retrieval	I-General_Concept
since	O
there	O
are	O
less	O
features	O
to	O
compare	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
first	O
three	O
color	B-Algorithm
moments	I-Algorithm
have	O
the	O
same	O
units	O
,	O
which	O
allows	O
for	O
comparison	O
between	O
them	O
.	O
</s>
<s>
Color	O
indexing	O
is	O
the	O
main	O
application	O
of	O
color	B-Algorithm
moments	I-Algorithm
.	O
</s>
<s>
Images	O
can	O
be	O
indexed	O
,	O
and	O
the	O
index	O
will	O
contain	O
the	O
computed	O
color	B-Algorithm
moments	I-Algorithm
.	O
</s>
<s>
Then	O
,	O
if	O
someone	O
has	O
a	O
particular	O
image	O
and	O
wants	O
to	O
find	O
similar	O
images	O
in	O
the	O
database	O
,	O
the	O
color	B-Algorithm
moments	I-Algorithm
of	O
the	O
image	O
of	O
interest	O
will	O
also	O
be	O
computed	O
.	O
</s>
<s>
,	O
,	O
and	O
are	O
weights	O
,	O
specified	O
by	O
the	O
user	O
,	O
for	O
each	O
of	O
the	O
three	O
color	B-Algorithm
moments	I-Algorithm
used	O
.	O
</s>
<s>
A	O
simple	O
and	O
concise	O
example	O
of	O
the	O
use	O
of	O
color	B-Algorithm
moments	I-Algorithm
for	O
image	B-General_Concept
retrieval	I-General_Concept
tasks	O
is	O
illustrated	O
in	O
.	O
</s>
<s>
The	O
first	O
three	O
color	B-Algorithm
moments	I-Algorithm
are	O
used	O
as	O
features	O
.	O
</s>
<s>
However	O
,	O
since	O
color	B-Algorithm
moments	I-Algorithm
are	O
invariant	O
to	O
scaling	O
,	O
it	O
is	O
not	O
necessary	O
to	O
make	O
all	O
images	O
the	O
same	O
width	O
and	O
height	O
.	O
</s>
<s>
Computing	O
the	O
features	O
-	O
Use	O
the	O
color	B-Algorithm
moments	I-Algorithm
formulae	O
in	O
order	O
to	O
compute	O
the	O
first	O
three	O
moments	O
for	O
each	O
of	O
the	O
color	O
channels	O
in	O
the	O
image	O
.	O
</s>
<s>
Calculating	O
the	O
similarity	O
score	O
-	O
After	O
computing	O
the	O
color	B-Algorithm
moments	I-Algorithm
the	O
weights	O
for	O
each	O
of	O
the	O
moments	O
in	O
the	O
function	O
should	O
be	O
determined	O
by	O
the	O
user	O
.	O
</s>
<s>
Ranking	O
and	O
image	B-General_Concept
retrieval	I-General_Concept
-	O
From	O
the	O
previous	O
step	O
the	O
values	O
were	O
obtained	O
.	O
</s>
