Image Processing Reference
In-Depth Information
Figure1.31 Near-UV image of polar bears. (Courtesy of Dr. David Lavigne)
transport gear on white sleds, all of which appear very dark when imaged in the
near-UV (350-380 nm), as shown in Fig. 1.32.
Ultraviolet light can penetrate some materials that are opaque to visible light
and can sometimes reveal information about underlying substances. This property
allows for noninvasive analysis of materials. For example, ultraviolet imaging
has an interesting application in dermatology. Human skin is normally opaque to
ultraviolet light, as the chemical pigment melanin absorbs it. Thus, people with
normally pigmented skin appear much darker in the ultraviolet than they do in the
visible. If the melanin is destroyed over time by exposure to ultraviolet light, it
can penetrate to sensitive inner layers and cause damage to the basal cells, which
are approximately 2 mm below the surface. The damaged skin will look white
in color—this is called actinic keratosis. Sometimes skin damage looks darker in
the UV band than in the visible band. This is because of hyperpigmentation—
the tendency of the skin to react to UV light damage by increasing the amount of
melanin in the skin. Light freckling will look much darker. Prior ultraviolet damage
Figure1.32 Visible
(left)
and
near-UV
(right)
images
of
Canadian
Arctic
military
camouflage. (Courtesy of Dr. David Lavigne)
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