With the development of visible light communication (VLC) and widespread applications of smart terminals with complementary- metal-oxide-semiconductor (CMOS) image sensor, researchers pay more and more attention in VLC systems with CMOS-based receiver. The blooming effect and light noise make the threshold decision in image processing difficult, which deteriorates the system performance a lot. In this paper, an efficient demodulation scheme is proposed to improve the performance of image processing. In the proposed demodulation scheme, a region of interest (ROI) based column matrix selection scheme is employed to avoid blooming effect, and an adaptive contrast enhancement (ACE) algorithm is designed to increase the contrast of bright and dark stripes. Experimental results show that the proposed scheme especially fits for high fluctuation data pattern. The demodulation with a data rate of 5.76 kbit/s can successfully achieve 7% forward error correction (FEC) limit even when the illuminance is very low.