Un-enhanced IR (water vapor)

The original image may be enhanced by contrast stretching. This method determines the minimum and maximum counts in the image and stretches the gray scale to cover the range from minimum to maximum count, eliminating counts not used in the base image. The gray bar at the bottom of this image indicates that portions of the un-enhanced 8-bit scale (both low and high values) are no longer used. In this case the ramp of gray shades lies between 8-bit counts of 156 and 222, or between temperatures of -21 degrees C [252 K] and -75 degrees C [198 K], since no values outside this range exist in the un-enhanced image. This image enhancement is much better than the un-enhanced image.

The first image may also be enhanced by the use of a fixed color enhancement table. In this enhancement the gray shades in the first image go through several color variations. The water vapor channel seldom sees temperatures above -10 degrees C [263 K] since no significant component of radiation comes from the earth's surface. Thus the yellow-green colors seldom appear except in the driest and warmest situations. Temperatures are shaded orange and black from about -13 degrees C [260 K] down to -29 degrees C [242 K] and then gray down to about -45 degrees C [228 K]. The transition from orange to gray shades occurs near the point where the temperature LUT changes slope. This is also the point where this channel transitions from seeing water vapor and temperature variations to measuring cloud top temperatures. For values colder than -45 degrees C, the colors change from magenta to cyan to green until about -71 degrees C [202 K], where the gray shades begin again. Only for the coldest cloud tops, below -78 degrees C [195 K], does the enhancement color change to blue, for temperatures which are seldom seen except for cloud tops in the tropics.