Image Processing Reference
Figure1.33 Visible (left) and near-UV (right) images of skin cancer. (Courtesy of Dr.
to skin is revealed with near-UV photography, as shown in Fig. 1.33. The near-UV
image was taken with conventional black-and-white film and a UV-transmitting
filter in the 350-380-nm waveband.
The visible image of skin on the patient's face appears fairly uniform, except
for an ulcerating basal-cell cancer on the bridge of her nose. The ultraviolet
photograph reveals many dark patches in the deep skin layers, some of which are
just hyperpigmentation, while others are precancerous lesions. There are also two
other basal-cell cancers on this patient: one on the nose just above the ulcerating
cancer and one under the left eye. This ultraviolet photography technique can aid
in earlier diagnosis of skin cancer, as precancerous lesions tend to look darker in
the ultraviolet than when viewed in the visible.
There are many animals and plants that have ultraviolet markings and patterns that
were visible only to animals with ultraviolet vision until UV imaging technology
revealed them to us. Some insects—notably bees—have visual sensitivity to
ultraviolet light in the 300-400-nm region of the spectrum. This ultraviolet vision
can see markings and patterns on flowers that we humans cannot. Figure 1.34
shows three Black-Eyed Susan flowers (Rudbeckiahirta) imaged in both the visible
and near-UV (350-380 nm) regions of the spectrum.
The visible image shows a uniform yellow color throughout, except for the dark
center, but the near-UV image reveals a complex pattern of light and dark zones,
which serve to guide the pollinating honeybee to its destination. These patterns
are known as nectar guides and are believed to play a role in insect pollination.