Look-up tables (LUT)
Instead of performing mathematical operations on every pixel in the image, the grey value is mapped in the so-called look-up table in a fraction of the time it would take to process each pixel. This is the reason why gamma correction is usually executed using look-up tables.
This technique is easy to implement in hardware and is a very efficient way of improving processing speed. Typical functions that can be implemented using LUTs include: changing image contrast and brightness, or applying a threshold to produce a bi-level (binary) image.