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Contrast
-- the range between light and dark objects in the image --
needs to be enhanced to emphasize color and brightness variations
and minimize the dulling effect of atmospheric haze. This is
done by digitally "stretching" the data so they span
the full range of possible brightness (many satellite images
are composed of 8-bit data, a possible range of 2**8 or 256
brightness values).
ETM images have eight different
spectral bands that sample discrete portions of the electromagnetic
spectrum ranging from visible wavelengths of light through thermal
infrared “heat.”
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The
image shown on here is a “natural color composite” of
ETM bands 3 (visible red light), 2 (green light), and 1 (blue
light), displayed using the colors red, green and blue, respectively.
Despite the name, this composite provides very poor color differentiation
on satellite imagery. |
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