In this paper we propose an efficient method to enhance contrast in real time in digital video streams by exploiting histogram variances and adaptively adjusting gamma curves. The proposed method aims to overcome the limitations of the conventional histogram equalization method, which often produces noisy, unrealistic effects in images. To improve visual quality, we use gamma correction technique and choose different gamma curves according to the histogram variance of the images. By using this scheme, the details of an image can be enhanced while the mean brightness level is kept. Experiment results demonstrate that our method is simple and efficient, and robust for both low and high dynamic scenes, and hence well suited for real-time, high-bit-depth video acquisitions.