Improved device and method for inquiry table capable of reducing memory use volume

An improved apparatus for reducing memory usage of look-up table mapping in an imaging system, a method related to the apparatus is also disclosed. The apparatus receives a digital input signal and processes it through a two-step mapping procedures instead of conventional skill that it uses only one look-up table, each procedure provides a series of mapping outputs. A comparing unit composed of a lot of logical gates is then comparing those mappings with original input signal and choosing the best one for preparing a final output. Finally, a final output corresponding to the best choice is providing for displaying.