(A) study on rolling shutter distortion correction and dynamic range widening in CMOS image sensor

Abstract

Due to remarkable improvements in CMOS image sensor (CIS) technology, the image sensor market, which has been dominated by CCD, is divided by the CCD and the CIS. While the CIS has advantages like process compatibility, low power consumption, and low supply voltage over the CCD, it has weak points like low signal-to-noise, narrow dynamic range, and rolling-shutter distortion. This thesis focuses on techniques to reduce rolling-shutter distortion and widen dynamic range. In Chapter 1, a technique to suppress the rolling-shutter distortion, coming from the unique readout mechanism of the CIS when there are fast-moving objects, is described. A mathematical analysis on rolling-shutter distortion is executed to derive an affine transformation between the distortion domain and the non-distortion domain in terms of motion vector and related sensor parameters. Based on the analysis, a post image processing scheme to compensate for the distortion is proposed. For motion vector detection, a modification of a well-known optical flow algorithm called Lucas-Kanade algorithm is utilized. Some experiments under artificial and real environment shows that the proposed motion detection algorithm provides accurate motion vectors at a reasonable computational complexity. A practical implementation of the post processing scheme including the motion vector detector is proposed which requires minimum HW resources when it is equipped on modern handheld devices. In chapter 2, a wide dynamic range (WDR) technique for the CIS with dual photodiode- pixel structure is proposed. The WDR capability can be achieved by synthesizing two differently exposed images acquired from two different-sized photodiodes assigned to one pixel. The maximum WDR capability is achieved from the sensor, when specialized automatic exposure controls are applied to both images. Using the proposed algorithm, a sensor can adaptively adjust its exposure to widely varying illumination conditions and consequently a...