A circuit for processing the outputs of an array of photoconductive detectors, includes amplifiers (101) for amplifying the detector outputs and analogue-to-digital converters (109) for digitizing the amplified outputs. The A to D converters oversample the detector signals. A digital processor (110) then applies a linearity correction to the digitized signals. The circuit is particularly suitable for processing the signals from an array of photoconductive detectors in an FT-IR microscope.