Mammography is at present the best available technique for early detection of breast cancer. Mammography is a low-dose x-ray procedure that allows visualization of the internal structure of the breast. Detection and diagnosis of breast cancer in its early stage increases the chances for successful treatment and complete recovery of the patient. Contrast enhancement of mammogram images is necessary to enable the radiologist to detect breast cancer in early stage. This paper presents contrast enhancement algorithm for assisting the analysis of digital mammograms. According to the radiologists' opinion, the best contrast enhancement method does not affect the normal breast tissue while enhances the suspicious regions. The proposed Selective Energy-Based Histogram Equalization (SEBHe) algorithm depends on this notice. The SEBHE algorithm uses only the image areas with high energy to build the histogram unlike conventional histogram equalization algorithm that enhances all pixels of the mammogram image as well as the background noise. Hence, the proposed algorithm enhances only the areas with high details and leaves the normal breast tissue without enhancement.