<s>
In	O
the	O
fields	O
of	O
computer	B-Application
vision	I-Application
and	O
image	B-General_Concept
analysis	I-General_Concept
,	O
the	O
scale-invariant	B-General_Concept
feature	I-General_Concept
operator	I-General_Concept
(	O
or	O
SFOP	O
)	O
is	O
an	O
algorithm	O
to	O
detect	O
local	O
features	O
in	O
images	O
.	O
</s>
<s>
The	O
scale-invariant	B-General_Concept
feature	I-General_Concept
operator	I-General_Concept
(	O
SFOP	O
)	O
is	O
based	O
on	O
two	O
theoretical	O
concepts	O
:	O
</s>
