What are look up tables in radiography? The gray-scale values in a digital image consist of binary numbers. It is possible to reassign these numbers to other values based on predetermined rules. These rules are defined in a look-up table (LUT) which is essentially a reference histogram. A look-up table (LUT) is a series of mathematical equations that are used for post-processing in radiography. It is used to correct values using a mapping function. It allows the gray-scale values in the recorded image to be remapped to new values to improve the final image in some way, such as appropriate brightness and contrast. LUTs are specific to anatomic areas.