Image Processing Reference
In-Depth Information
Figure1.9 Near-IR image showing dark-adapted eyes. (Courtesy of Dannen Harris)
Eastman Kodak, Inc. led to the invention of high-speed infrared film. The first
commercial infrared film based on kryptocyanine had low sensitivity and was
therefore unsuitable for military applications. Kodak's high-speed film made it
possible to detect camouflage with aerial reconnaissance. Figure 1.10 shows three
views of a factory, reproduced from a Kodak advertisement from 1943. The top
image shows a standard aerial picture of a factory, a high-value target that can be
very easily spotted from the air.
The middle image shows a conventional visible-light photograph of the factory
covered with camouflage (netting, green cloth, artificial trees). The factory is quite
well concealed, at least from reconnaissance aircraft forced to fly at high altitudes
to avoid anti-aircraft artillery. The bottom image is a picture of the camouflaged
factory made with Kodak Aero Infrared film, a film that is sensitive in both the
visible and the near-IR wavebands out to about 900 nm.
Unlike real vegetation, which is highly reflective in the infrared, the artificial
vegetation appears black in the infrared image, since the green cloth and netting
material does not reflect infrared well. Notice that the real grass and vegetation in
the near-IR image appears snow-white; this is healthy vegetation, which has a very
high reflectivity to near-IR light due to the presence of the molecules chlorophyll
and xanthophyll. Diseased, dehydrated, or otherwise stressed vegetation shows a
marked decrease in near-IR reflectivity, and agriculturists exploit this property of
vegetation in remote sensing applications, as shown in the next example of near-IR
imaging.
Leaves and grass are highly reflective in the near-IR band, and infrared
photography is often used to evaluate the extent of urban development, since it
enhances the visual contrast between “green space” and built-up areas. Figure 1.11
is a LANDSAT image of the San Francisco peninsula in California, which has a
different color representation than that of our eyes due to the varying levels of IR
reflectance. This is known as pseudocolor or false color, and we will encounter
it repeatedly in this topic as a means of visually representing invisible wavebands
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