Accurate segregation of pectoral muscles is very crucial in breast cancer detection. Pectoral segmentation is a challenging task due to heterogeneous tissues densities, neighborhood complexities and breast shape variabilities. This paper presents an adaptive gamma correction method for pectoral suppression in mammograms. The proposed algorithm is adaptive to variations in shape, density of tissues and the curvature of pectoral boundary i.e. straight line or curved pectoral boundary. The method utilizes the morphological information of mammograms to discriminate the breast parenchyma from the rest of breast region. The adaptive gamma corrections enhance the mammograms according to tissues densities and provide a separation boundary between breast region and pectoral parenchymal. The method is tested on three types of tissues densities present in MIAS dataset i.e. Fatty, Fatty-glandular and Dense tissues. The goodness of segmentation is measured using jaccard similarity index between the ground truth and segmented regions. The proposed methods successfully detected 98.45 % of the pectoral regions and have an overall 92.79 % jaccard similarity index with the ground truth. Moreover, evaluation by experts also confirms good performance of the proposed method.