I. Introduction
The miniaturization of image acquisition devices has made it possible to implement video-recording devices in the design of nearly all types of smart devices, including mobile phones, portable computers, and TVs. At the center of this miniaturization is the complementary metal-oxide semiconductor (CMOS) image sensor (CIS); however, the CIS is sensitive to environmental noise signals because of a relatively small corresponding photocell. In low-light environments, both the image signals and the noise signals are mixed and are boosted by the automatic gain control (AGC), resulting in a less desirable image quality.