
where
^
Hu, v, wðÞis the 3-D Fourier transform of
^
hx, y, zðÞ,‘‘
*
’’ is the complex
conjugation operation, and P
w
u, v, wðÞand P
f
u, v, wðÞare the power spectral
densities of the noise and the specimen, respectively [30]. Equation 14.11 can be
rewritten as
^
Hu, v, wðÞ¼
1
Hu, v, wðÞ
Hu, v, wðÞ
jj
2
Hu, v, wðÞ
jj
2
þ
1
SNR u
, v, wðÞ
"#
(14:12)
where
SNR u, v, w
ðÞ
¼
P
f
u, v, wðÞ
P
w
u, v, wðÞ
Equation 14.12 can be interpreted as two filters in cascade in the frequency
domain, where 1=H(u, v, w ) is the inverse filter and the term in brackets is the
Wiener filter. The term SNR(u, v, w) is the signal-to-noise ratio as a function of
frequency. In the absence of noise, (i.e., infinite