Automatic exposure (AE) is one of the indispensable functions of modern video cameras. According to the attention mechanism of human visual systems, peak regions in luminance histogram correspond to the region of no interest in an image. Based on this assumption, a new AE algorithm using the luminance histogram of an image is proposed in this paper. The algorithm finds the first two largest peak regions in the histogram and calculates the mean weighted luminance (MWL) of the entire image by weighting the luminance of pixels inside the two peak regions. The MWL is then used to control the exposure of video cameras. The weight of pixel luminance is decided by a set of quadratic curves, and the parameters of the quadratic curves are affected by the brightness of the image background. Fuzzy logic is also applied to optimize the practical AE systems. Results show that the proposed algorithm gives efficient exposure control over various scene tests.