The look-up table function rescales the temperatures from the current image within the limits imposed by the user. These limits must be inside the temperature domain of the original image.
'dam' original image
image processed with 'look-up table'
The original image had temperatures between 13.7 and 24.1 degrees Celsius. The new limits were selected by the user (19.9 - 22.0 deg C) and the important zones (the big crack in the dam) show up more acurately in the processed image.
The temperatures (inside the new limits) from the processed image stay the same as the ones from the original.