An efficient demosaiced image enhancement method for a low cost single-chip CMOS image sensor (CIS) with an on-chip image signal processor (ISP) is proposed. In a single-chip CIS for handheld devices that requires low power consumption, the ISP implemented must be as small as possible while maintaining high performance. Demosaicing and image enhancement are the largest block in the ISP because they need line memories. In this paper, we propose a new method to minimize the number of line memories. In the proposed method, buffered data for demosaicing were used to make approximated luminance data for image enhancement. This enables line memory sharing between demosaicing and image enhancement. The experimental results showed that the proposed method enhanced the image quality. Thus, both high quality and a small area can be achieved by utilizing the proposed method.