A device includes an offset subtraction unit; an image sensor which receives, for each of a plurality of bright frames, a respective image signal obtained during a respective exposure time of the image sensor, and transmits the same to the offset subtraction unit, and receives, for a dark frame, a respective image signal obtained during a respective exposure time of the image sensor, and transmits the same to the offset subtraction unit; and a control unit which ensures that the image sensor alternately transmits a number of bright frames and one dark frame to the offset subtraction unit. An amount of light by which the respective image signal for each of the bright frames is generated is larger than an amount of light by which the respective image signal for the dark frame is generated; and the offset subtraction unit obtains an offset and subtracts the offset from a signal.