This paper presents an approach to low light image contrast enhancement whose objective is to improve the visual quality of an image. To this end, a linear image fusion with two images is applied in this study. The two images are the input image and its histogram equalized image. For better performance, we use a metaheuristic optimization algorithm called the whale optimization algorithm to find an optimal weight for the linear fusion, where a patch-based contrast quality index is used as a fitness function. The proposed approach is verified by hundreds of low contrast images. The result indicates that our approach has a superior performance to the comparison approaches, conventional histogram and contrast limited adaptive histogram equalization in terms of patch-based contrast quality index and subjective visual quality.