Importance

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Abstract

A document reader comprises line sensors that are staggeredly arranged and read a white reference plate to obtain a white reference read value A, and a white reference average value AA is determined from value A for each line sensor. The line sensors read another white reference plate placed on a document support plate to obtain a white reference read value B, and a white reference read average value BB is determined from value B for each line sensor. A sensitivity effect coefficient C for each line sensor is determined by dividing BB by AA. Using the line sensors, there are obtained a document read value E for each line sensor by reading an illuminated document on the document support plate, a white reference read value Aa by reading with the white reference plate before reading the document, and a black reference read value D by reading the white reference plate under a condition that an illumination is turned off before reading of the document. Shading for the line sensors is corrected using the coefficient C, the values Aa, D and E, and a number of gradation levels for image regions corresponding to read areas of the document.

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First Claim