Patent ID: 8405884

Claim:
A scanner comprising: a transparent plate; a light emitting unit that emits light to an object disposed on the transparent plate; a sensor that detects light from the object, to acquire an image of the object; a focusing lens unit disposed on a light path between the transparent plate and the sensor, to focus light from the object onto the sensor; and a controller that determines whether a foreign substance is disposed on the light path, by analyzing the image acquired by the sensor, calculates the position of the foreign substance, and corrects the image on the basis of the calculated position of the foreign substance; wherein the controller filters a shading profile of the image, to determine whether the foreign substance is disposed in the light path, and calculates a distance between the focusing lens unit and the foreign substance based on both of a depth of a defective portion of the shading profile corresponding to the foreign substance and a width of the defective portion.