Figure 1-15.—Illustration of a basic enhancement curve table.

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