Mobile cameras have come a long way since their evolution and have replaced digital still cameras. However, their lowlight photography performance needs significant improvement. Dual camera systems consisting of a monochrome sensor and a Bayer sensor offer us a way to improve the low-light photography. The existing dual camera systems use post-processing methods after Image Signal Processor (ISP) for image fusion which are computationally intensive and use two ISPs. We propose a novel architecture in which the image fusion can be done in Bayer domain prior to the ISP. This helps us realize image fusion using only one ISP and also reduces power consumption, making it a viable solution for smart phones. The proposed system also gives better quality images than existing systems.