Image enhancement achieved by various contrast enhancement methods. (A) Subimage of mammographic image mdb003. (B) Phantom features of well-circumscribed masses m1, m2, and m3 of different diameters. (C) Simulated image; ROIs that include each phantom feature are denoted as R1, R2, and R3. (D-I) Contrast enhanced images obtained by the following methods: the proposed method (D), histogram equalization (E), linear contrast stretching (F), unsharp masking (G), multiscale retinex (H), and contrast limited adaptive histogram equalization (I).