Patent ID: 7872784

Claim:
An image reading apparatus for reading images of both sides of a document sheet, comprising: a first reader, arranged to read a front image of the document sheet; a second reader, arranged to read a backside image of the document sheet; an extractor, arranged to generate first histograms of plural color components from image data of the image read by said first reader to extract a first background color of the image read by said first reader using the first histograms, and to generate second histograms of the plural color components from image data of the image read by said second reader to extract a second background color of the image read by said second reader using the second histograms; a first color processor, arranged to apply color processing to the image read by said first reader using a first lookup table; a second color processor, arranged to apply color processing to the image read by said second reader using a second lookup table; and an adjustor, arranged to adjust output values of grid points of the first or second lookup table so as to make an output of said first color processor for the first background color be approximately equal to an output of said second color processor for the second background color, wherein the grid points of the first lookup table correspond to vertices of a three-dimensional shape which encloses the first background color extracted by said extractor, and the grid points of the second lookup table correspond to vertices of a three-dimensional shape which encloses the second background color extracted by said extractor, and wherein said adjustor adjusts either the output values of the grid points of the first lookup table or the output values of the grid points of the second lookup table so that adjustment amounts of the output values are those of which are smaller with respect to a relationship between the first lookup table and the second lookup table.