Patent ID: 8493632

Claim:
An image reading apparatus that performs shading correction by decreasing a number of gradations of white reference data and black reference data to below a number of gradations of image data to be read, comprising: a gain setting section that sets a gain of a signal output by an image sensor; a reference data reading section that reads the white reference data and the black reference data amplified by the gain; an image reading section that reads the image data amplified by the gain; a correction data generation section that generates correction data by synthesizing a substring extracted from the white reference data with a substring extracted from the black reference data; and a correction section that performs shading correction of the image data read by the image reading section by using the correction data, wherein in a case where the black reference data is equal to or greater than a predetermined threshold value L, the gain setting section performs resetting to lower the gain that has been set, the reference data reading section rereads the black reference data using the reset gain, and the correction data generation section generates correction data by synthesizing the substring of the white reference data with the substring of the black reference data that has been reread.