An active pixel image sensor comprises a pixel array of active pixels that are capable of being random access addressed to provide pixel readout signals from the addressed pixels on N output lines, where N is a plural integer and M ADC lanes capable of performing analog-to-digital conversion of pixel readout signals, where M is a plural integer less than N. A switching arrangement is capable of selectively connecting output lines to the M ADC lanes. A control unit provides random access addressing of the pixels, and in synchronisation therewith controls the switching arrangement to connect the output lines on which the addressed pixels provide pixel readout signals to ADC lanes.