1. A method of performing adaptive contrast enhancement according to image types, the method comprising: reading an image; calculating a mean luminance value and luminance histogram of the image; determining a type of the image based on the mean luminance value and the luminance histogram; creating contrast reference curves by applying different coefficients according to image types to a hyperbolic tangential function curve; and performing contrast enhancement of the image by using the contrast reference curves; wherein the type of the image is determined as a low lighting image in a case of 0<the mean luminance value≦50, a regular lighting image in a case of 50<the mean luminance value≦200, a back lighting image in a case of 200<the mean luminance value≦255, and a high contrast image in a case in which a maximum number of pixel counts is represented at both high and low luminance values in luminance histogram distribution.