What are Response Linearization Look Up Tables?
Response Linearization Look Up Tables (RLUT) are optional additional files that accompany Calibration Parameter Files (CPF) and contain a mapping look up table to linearize the output of the OLI detectors.
This is done to increase the range of Digital Number (DN) values for preciseness and limit the number of saturated pixels to true saturations, and on the dark end, limit it to missing data.
Non-linearity characterization uses a series of variable integration time observations of the solar diffuser and corresponding shutter observations to generate a remapping for every digital number (4096 values per detector) for every detector.
RLUT files can be downloaded from this USGS website: Response Linearization Look Up Tables.