The fundamental reason of contrast enhancement is to bring out detail that is hidden in an image that is covered up in a picture or to expand contrast in a low contrast picture. This paper presents a literature survey on some of the image Enhancement techniques for improving images like histogram equalization, global histogram equalization, bi-histogram equalization, dualistic sub-image histogram equalization, Spatial Domain Method and Frequency Domain Method etc. The overall objective of this paper is to evaluate the short comings in earlier techniques of image enhancement.