Patent ID: 6891648

Claim:
An image-reading device comprising: a subject-copy-conveying path conveying a subject copy; a photoelectric converting element placed on said subject-copy-conveying path so as to read a first image from a surface of said subject copy; a read roller placed opposite said photoelectric converting element with said subject-copy-conveying path therebetween so as to keep a distance constant between said surface of said subject copy and said photoelectric converting element by revolving, a surface of the read roller functioning as a reference white used in a white-shading correction; reading means for reading a second image from a constant range on said surface of said read roller by using said photoelectric converting element; averaging means for dividing image data of said second image into a plurality of blocks in a sub-scanning direction so that each of the blocks includes a plurality of lines, and obtaining average values of image data of said lines in said blocks respectively; peak-value determining means for obtaining a peak value of said average values; and white-shading correcting means for performing the white-shading correction to image data of said first image by using said peak value as white-shading data, wherein said constant range is a range exceeding one round on said surface of said read roller; and a length of each of said blocks in the sub-scanning direction is so set that, when said constant range is divided into said blocks, a fractional block is created in each round of said constant range.