Patent ID: 7102787

Claim:
An image reading apparatus comprising an image reader for reading an original image to produce digital image data, a correction coefficient memorizing circuit for memorizing shading correction coefficient data, and a correction coefficient multiplying circuit connected to said correction coefficient memorizing circuit for multiplying said digital image data by said shading correction coefficient data to produce a result of multiplication as shading corrected image data, said image reading apparatus further comprising: a correction coefficient determining circuit responsive to white reference data of a white reference plate read by said image reader before reading said original image for determining a correction coefficient per each bit of said white reference data in a bit array along a main scanning direction; a correction coefficient modifying circuit connected to said correction coefficient determining circuit for producing a modified correction coefficient; and a correction coefficient predicting circuit connected to said correction coefficient modifying circuit for producing a predicted correction coefficient with reference to said modified correction coefficient and sending said predicted correction coefficient to said correction coefficient modifying circuit; said correction coefficient modifying circuit being supplied with said correction coefficient and said predicted correction coefficient and producing said correction coefficient and said predicted correction coefficient as said modified correction coefficient when an absolute value of a difference between said correction coefficient and said predicted correction coefficient is smaller than and when said absolute value is not smaller than a predetermined threshold value, respectively; said correction coefficient memorizing circuit memorizing said modified correction coefficient as said shading correction coefficient data.