T. Tajbakhsh and R.-R. Grigat (Germany)
Illumination flicker, 50 Hz/60 Hz classification, rolling shutter, AC power frequency, Video Processing
In many modern imagers employing CMOS pixel arrays the optical integration time is controlled by a rolling shut ter. This integration technique, combined with fluorescent illuminators exhibiting an alternating light intensity, causes spatial flicker in images. This flicker can be avoided when the integration time of the imager is adjusted to a multi ple of the flicker period. Since the flicker frequency can vary upon the local AC power frequency, a classification must be performed beforehand. This is either performed utilizing an additional illumination intensity detector or, in the case we focus on, restricting to image information only. In this paper we review the state of the art techniques of flicker frequency classification and flicker correction, and propose two robust classification methods based on a clear mathematical model of the illumination flicker problem. We present our simulation results with synthesized image series under diļ¬erent illumination frequencies and shutter widths, whereas our approaches classify robustly in most imaging situations.
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