Reversible data hiding (RDH) can extract secret messages and restore the original image without distortion. The reversibility benefits many practical applications such as medical image processing and multimedia archive management. Because of high image quality, histogram modification is applied to RDH in many literatures. In this paper, two-dimensional histogram and prediction-error expansion are integrated with a well- designed difference-pair mapping (DPM) to improve embedding capacity. According to the simulation results, the proposed RDH scheme outperforms existing approaches, which are also based on two-dimensional histogram. On the average, image quality is improved by 3dB with the same embedding capacity. Maintaining at the same image quality, embedding capacity can be improved by approximately 30,000 bits.