Imaging apparatus (100, 200) includes a photosensitive medium (302) configured to convert incident photons into charge carriers. A bias electrode (304) overlies the photosensitive medium and applies a bias potential to the photosensitive medium. One or more pixel circuits (306) are formed on a semiconductor substrate. Each pixel circuit defines a respective pixel (300) and includes first and second pixel electrodes (316, 318) coupled to collect the charge carriers from the photosensitive medium at respective first and second locations, and first and second transfer gates (326, 328) in respective proximity to the first and second pixel electrodes. Circuitry (700) is coupled to apply different, respective first and second potentials to the first and second transfer gates and to vary the first and second potentials so as to control relative proportions of the charge carriers that are collected by the first and second electrodes.