Digital Signal Processing Reference
In-Depth Information
Figure 3.18. (top left) Hale-Bopp comet image. (top right)
Ophthalmic medical image. (middle) Histogram equalization
results. (bottom) Wavelet-log representations.
Wavelets can be used to compress the dynamic range at all scales and therefore
allow us to clearly see some very faint features. For instance, the wavelet-log repre-
sentation consists of replacing
w
j
[
k
,
l
]bysign(
w
j
[
k
,
l
]) log(
|
w
j
[
k
,
l
]
|
), leading to the
alternative image
J
l
]) log(
w
j
[
k
l
]
+
X
[
k
,
l
]
=
log(
c
J
[
k
,
l
])
+
sign(
w
j
[
k
,
,
)
,
(3.52)
j
=
1
10
−
3
).
Figure 3.18 shows a Hale-Bopp comet image (top left) and an ophthalmic medi-
cal image (top right), their histogram equalization (middle row), and their wavelet-
log representation (bottom). Jets clearly appear in the last representation of the
Hale-Bopp comet image, and many more features are distinguishable in the wavelet
log representation of the ophthalmic medical image.
=
where
is a small number (e.g.,
