Look Up Table. A memory which is used to perform tabulate the results of a calculation. The memory address is formed from the input to the calculation, and the memory contents are the result of the calculation. All possible calculations must be performed in advance, with the results forming the (static) look up table.
Lookup table, a means of storing data that would otherwise require an unreasonable amount of resources. For example, a palette is a type of lookup table that allows image data to be encoded indirectly, thereby reducing its overall space requirements. Gamma correction, on the other hand, has potentially large computational requirements, since it involves the use of exponential functions. Calculating the exponentials once for every possible sample value and storing the results in a lookup table is almost always more efficient than computing an exponential for every sample in the image.