<s>
Shape	B-Algorithm
from	I-Algorithm
focus	I-Algorithm
or	O
shape	B-Algorithm
from	I-Algorithm
defocus	I-Algorithm
is	O
a	O
method	O
of	O
3D	B-Algorithm
reconstruction	I-Algorithm
which	O
consists	O
of	O
the	O
use	O
of	O
information	O
about	O
the	O
focus	O
of	O
an	O
optical	O
system	O
to	O
provide	O
a	O
means	O
of	O
measurement	O
for	O
3D	O
information	O
.	O
</s>
<s>
In	O
its	O
most	O
simple	O
form	O
,	O
the	O
methods	O
analyze	O
an	O
image	O
based	O
upon	O
overall	O
contrast	O
from	O
a	O
histogram	B-Algorithm
,	O
the	O
width	O
of	O
edges	O
,	O
or	O
more	O
commonly	O
,	O
the	O
frequency	O
spectrum	O
derived	O
from	O
a	O
fast	O
Fourier	O
transform	O
of	O
the	O
image	O
.	O
</s>
