Scanner and shading correction method

A scanner comprising:

• an image scanning mechanism including
• a light source that emits light for irradiating a scan object,
• an optical system including a mirror, and
• an image sensor having photoelectric conversion elements arranged in line in a main scanning direction,
• the image scanning mechanism introducing reflected light of the emitted light from the scan object into the image sensor via the optical system and obtaining an image data corresponding to an image of the scan object with the image sensor;
• a foreign object location detector that detects a pixel at a foreign object location at which a local drop in luminance due to a foreign object adhered to the optical system is indicated in a waveform of a first reference image data showing a relationship between locations in the main scanning direction of pixels corresponding to the respective photoelectric conversion elements and luminance values of the respective pixels, based on the first reference image data obtained by scanning a white reference plate by the image scanning mechanism at an initial operation after power-on of the scanner;
• a foreign object location storage that stores a location in the main scanning direction of the pixel at the foreign object location detected by the foreign object location detector;
• a correction processor that corrects luminance values of all pixels within a second range including the pixel at the foreign object location within a first range in the main scanning direction centered on the pixel at the foreign object location stored in the foreign object location storage so as to be a value calculated by using a difference value between a luminance value of a pixel at one end of the first range and a luminance value of the pixel at the foreign object location, with respect to a second reference image data obtained by scanning the white reference plate by the image scanning mechanism at a scanning operation of an original;
• and
• a shading correction processor that performs a shading correction to an original image data obtained by scanning the original by the image scanning mechanism by use of the second reference image data corrected by the correction processor.