COUNT VALUE INPUT
Figure 1-15.—Illustration of a basic enhancement curve table.
solid line (AB) represents a case of no enhancement.
As an example, if you acquired an image and the
warmer (darker) end of the spectrum required greater
definition, the data could be modified as illustrated by
the segment (AC). In this case, all the gray shades from
+56.0°C to 5.8°C would be displayed.
Enhancement curves for high-resolution imagery
from DMSP and NOAA satellites are usually
developed based upon three basic configurations,
depending on desired results. They are the single
enhancement, the high-low enhancement, and the split
enhancement.
SINGLE ENHANCEMENT.—The single
enhancement curve is defined over a complete count
value range, but for either a default or specified
temperature range. This curve will give you all gray
shades across your defined temperature range. For
example, if you were interested in only low clouds or
sea surface temperatures, you might only enhance the
image in a range from +20°C to -10°C, as shown in
figure 1-16. Any areas on the image colder than the
lower limit will appear white. Areas warmer than the
upper limit will appear black.
HIGH-LOW ENHANCEMENT.—For high-
low enhancement curves, two ranges are selected. For
each of these, a unique part of the gray-shade and count
value scale is applied to each range. Thus, warm
temperatures may be in the gray-black range, while
cold temperatures may be in the white off-white range.
Figure 1-17 is an example of a high-low enhancement
curve with temperature ranges of +30°C to +05°, and
-20°C to -40°C. Areas colder than the lowest
minimum temperature will appear white. Areas
warmer than the highest maximum temperature will
appear black. Areas which are temperatures between
the upper and lower ranges will appear black.
1-16
