There is provided a signal-processing device which processes transparent images each expressed by transparent superimposition of a target portion such as an affected part and a background portion. The device includes a transparent image acquiring unit that acquires the transparent images each including the target portion at a plurality of times a calculating unit that calculates a component of the transparent image originating from the target portion and a component of the transparent image originating from the background portion at a given time t among the plurality of times in association with an estimated value of distribution information of the target portions and the background portions and that evaluates consistency with the transparent images and an updating unit that updates the estimated value of the distribution information of the target portion or the background portion at the time t based on the evaluation result of the calculating unit.
