<s>
In	O
computer	B-Application
vision	I-Application
,	O
the	O
Marr	B-Algorithm
–	I-Algorithm
Hildreth	I-Algorithm
algorithm	I-Algorithm
is	O
a	O
method	O
of	O
detecting	B-Algorithm
edges	I-Algorithm
in	O
digital	B-Algorithm
images	I-Algorithm
,	O
that	O
is	O
,	O
continuous	O
curves	O
where	O
there	O
are	O
strong	O
and	O
rapid	O
variations	O
in	O
image	O
brightness	O
.	O
</s>
<s>
The	O
Marr	O
–	O
Hildreth	O
edge	B-Algorithm
detection	I-Algorithm
method	O
is	O
simple	O
and	O
operates	O
by	O
convolving	O
the	O
image	O
with	O
the	O
Laplacian	O
of	O
the	O
Gaussian	O
function	O
,	O
or	O
,	O
as	O
a	O
fast	O
approximation	O
by	O
difference	B-Algorithm
of	I-Algorithm
Gaussians	I-Algorithm
.	O
</s>
<s>
Then	O
,	O
zero	B-Algorithm
crossings	I-Algorithm
are	O
detected	O
in	O
the	O
filtered	O
result	O
to	O
obtain	O
the	O
edges	O
.	O
</s>
<s>
Today	O
,	O
there	O
are	O
much	O
better	O
edge	B-Algorithm
detection	I-Algorithm
methods	O
,	O
such	O
as	O
the	O
Canny	B-Algorithm
edge	I-Algorithm
detector	I-Algorithm
based	O
on	O
the	O
search	O
for	O
local	O
directional	O
maxima	O
in	O
the	O
gradient	O
magnitude	O
,	O
or	O
the	O
differential	O
approach	O
based	O
on	O
the	O
search	O
for	O
zero	B-Algorithm
crossings	I-Algorithm
of	O
the	O
differential	O
expression	O
that	O
corresponds	O
to	O
the	O
second-order	O
derivative	O
in	O
the	O
gradient	O
direction	O
(	O
both	O
of	O
these	O
operations	O
preceded	O
by	O
a	O
Gaussian	O
smoothing	O
step	O
)	O
.	O
</s>
<s>
For	O
more	O
details	O
,	O
see	O
the	O
article	O
on	O
edge	B-Algorithm
detection	I-Algorithm
.	O
</s>
