Imaging apparatus (20) includes a photosensitive medium (22) and a bias electrode (32), which is at least partially transparent, overlying the photosensitive medium. An array of pixel circuits (26) is formed on a semiconductor substrate (30). Each pixel circuit includes a pixel electrode (24) coupled to collect the charge carriers from the photosensitive medium; a readout circuit (75) configured to output a signal indicative of a quantity of the charge carriers collected by the pixel electrode; a skimming gate (48) coupled between the pixel electrode and the readout circuit; and a shutter gate (46) coupled in parallel with the skimming gate between a node (74) in the pixel circuit and a sink site. The shutter gate and the skimming gate are opened sequentially in each of a sequence of image frames so as to apply a global shutter to the array and then to read out the collected charge carriers via the skimming gate to the readout circuit.