DOCUMENT READING METHOD, DOCUMENT READER, IMAGE FORMING DEVICE, AND IMAGE SCANNER

摘要

Photoelectric conversion elements of line sensors (CIS22 to CIS26) staggeredly arranged read a white reference plate to acquire a white reference read value A, and a white reference read average value AA is determined from the white reference read value A for each line sensor. Further the photoelectric conversion elements read another white reference plate placed on a document support plate to acquire a white reference read value B, and a white reference read average value BB is determined from the white reference read value B for each of the line sensors (CIS22 to CIS26). Using the white reference read values AA, BB a sensitivity effect coefficient C used for uniforming the sensitivities different because of the variation of the distances from the line sensors (CLS22 to CLS26) to the document support plate is determined by dividing the average value BB by a data processing section for each of the photoelectric conversion element of the line sensors. By using a white reference read value Aa acquired by reading a white reference plate immediately before reading a document and a black reference read value, a white reference read value Aa for shading correction for correcting a document read value E is corrected with the sensitivity offset coefficient C. In such a way, irrespective of the variation of the distances from the line sensors to the document support plate, the variation of the document read values read from the photoelectric conversion element of the line sensors can be suppressed.