<s>
The	O
census	B-Algorithm
transform	I-Algorithm
(	O
CT	O
)	O
is	O
an	O
image	O
operator	O
that	O
associates	O
to	O
each	O
pixel	B-Algorithm
of	O
a	O
grayscale	O
image	O
a	O
binary	O
string	O
,	O
encoding	O
whether	O
the	O
pixel	B-Algorithm
has	O
smaller	O
intensity	O
than	O
each	O
of	O
its	O
neighbours	O
,	O
one	O
for	O
each	O
bit	O
.	O
</s>
<s>
It	O
has	O
applications	O
in	O
computer	B-Application
vision	I-Application
,	O
and	O
it	O
is	O
commonly	O
used	O
in	O
visual	O
correspondence	B-Algorithm
problems	I-Algorithm
such	O
as	O
optical	O
flow	O
calculation	O
and	O
disparity	O
estimation	O
.	O
</s>
<s>
The	O
census	B-Algorithm
transform	I-Algorithm
is	O
related	O
to	O
the	O
rank	B-Algorithm
transform	I-Algorithm
,	O
that	O
associates	O
to	O
each	O
pixel	B-Algorithm
the	O
number	O
of	O
neighbouring	O
pixels	B-Algorithm
with	O
higher	O
intensity	O
than	O
the	O
pixel	B-Algorithm
itself	O
,	O
and	O
was	O
introduced	O
in	O
the	O
same	O
paper	O
.	O
</s>
<s>
The	O
results	O
of	O
these	O
comparisons	O
are	O
concatenated	O
and	O
the	O
value	O
of	O
the	O
transform	O
is	O
an	O
8-bit	O
value	O
,	O
that	O
can	O
be	O
easily	O
encoded	O
in	O
a	O
byte	B-Application
.	O
</s>
<s>
Similarity	O
between	O
images	O
is	O
determined	O
by	O
comparing	O
the	O
values	O
of	O
the	O
census	B-Algorithm
transform	I-Algorithm
for	O
corresponding	O
pixels	B-Algorithm
,	O
using	O
the	O
Hamming	O
distance	O
.	O
</s>
<s>
whose	O
result	O
can	O
be	O
encoded	O
with	O
two	O
bits	O
for	O
each	O
neighbour	O
,	O
thus	O
doubling	O
the	O
size	O
of	O
the	O
pattern	O
for	O
each	O
pixel	B-Algorithm
.	O
</s>
