Motion tracking using multiple exposures

Imaging apparatus (100, 200) includes a photosensitive medium (304) configured to convert incident photons into charge carriers and a common electrode (306), which overlies the photosensitive medium and is configured to apply a bias potential to the photosensitive medium. An array (202) of pixel circuits (302) is formed on a semiconductor substrate (312). Each pixel circuit defines a respective pixel (212) and collects the charge carriers from the photosensitive medium while the common electrode applies the bias potential and to output a signal responsively to the collected charge carriers. Control circuitry (208) reads out the signal from the pixel circuits in each of a periodic sequence of readout frames (500) and drives the common electrode to apply the bias potential to the photosensitive medium during each of a plurality of distinct shutter periods (506, 702, 704, 902, 904) within at least one of the readout frames.