where is the orientation,
s
controls the spread about that orientation and
l
is the angle is
local orientation focus. The other spreading function is a band-pass filter, here a log-Gabor filter
lg with M different scales.
lg

m
=
0 =0
1
2
e
log
m

2
2
log

2
=0
(4.37)
where is the scale, controls bandwidth at that scale and
m
is the centre frequency at that
scale. The combination of these functions provides a 2D filter l2Dg which can act at different
scales and orientations.
l2Dg