Abstract: The purpose of image enhancement is to make images better than the original so that they become clearer and they can be easily interpreted. The image enhancement techniques may have spatial domain or frequency domain. But the researchers have proved that frequency domain techniques are better than spatial domain techniques. Today optimization algorithms are used in the approach used for image enhancement. This paper reviews the various image enhancement techniques.

Keywords: DWT, SVD, CLAHE, DCT, Cuckoo Search Algorithm, Bacterial Foraging Optimization Algorithm