Image Processing Reference
In-Depth Information
Figure2.30 Visible (left) and MWIR (3-5 mm) (right) images of a fingertip. (Courtesyof
Stress injuries such as repetitive motion injury can also be diagnosed with thermal
imaging—the affected limb or digit will show excessive surface temperatures.
Figure 2.30 is an MWIR image of a fingertip taken with a close-up lens. The
sweat glands cool the skin through evaporation and thus show up as small cold
dark spots, corresponding to a cooler temperature. Thermal imaging is used to
study the mechanism of perspiration and the distribution of sweat glands in skin.
Biological systems, like industrial machines, have to manage thermal energy
in order to function properly. The chemical reactions that govern the functioning
of biological systems are quite sensitive to temperature, and most organisms
will die if their internal temperature fails to stay within a particular range.
A failure to properly regulate the temperature of living tissue may be due to
environmental causes, disease, injury or some other condition, and the detection
of thermal anomalies in tissue is often a vital part of biological and medical
research. Scientists use thermal imaging to measure temperature, since it makes
it possible to monitor the surface temperature of organisms at many points
simultaneously without physical contact. Surface temperatures can sometimes be
used to determine the internal temperature of an organism, especially in cases
where the organism is fairly small, as is the case with hummingbirds, shrews
and insects, for example. This hummingbird in Fig. 2.31 shows a peak surface
temperature around the eyes of31 : 6 C(88 : 88 F), as measured by a calibrated
MWIR camera.
An interesting case of an insect's failure to maintain body temperature is found
in Japan. The Japanese honeybee Apis japonica has developed a novel defense
against predatory hornets. When a hornet approaches a hive, the bees will often
sense its chemical odor. They will mass around the hornet in a ball and begin
shivering their muscles rapidly, creating a hot blanket around the hornet. The
temperature inside the ball reaches47 C(116 : 6 F), which is one degree hotter
than the maximum temperature that the hornet can withstand, but only one degree
cooler than the maximum temperature the bees can withstand. The bees are right
at the edge of survival and are just barely able to kill the hornets without killing
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