Patent ID: 8405887

Claim:
A shading correction method for a scanner including an image scanning mechanism for emitting light to irradiate a scan object, introducing reflected light from the scan object into an image sensor that has photoelectric conversion elements arranged in line in a main scanning direction via an optical system including a mirror, and obtaining an image data corresponding to an image of the scan object with the image sensor, the shading correction method comprising: obtaining a first reference image data by scanning a white reference plate by the image scanning mechanism at an initial operation after power-on of the scanner; detecting 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 the 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; storing in a foreign object location storage a location in the main scanning direction of the pixel at the foreign object location; obtaining a second reference image data by scanning the white reference plate by the image scanning mechanism at a scanning operation of an original; correcting 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 the second reference image data; and performing a shading correction to an original image data obtained by scanning the original by the image scanning mechanism by use of the corrected second reference image data, wherein the luminance values of the pixels within the second range in the second reference image data corrected by the correction processor are smaller that the luminance value of the pixel at the foreign object location before correction.