Patent ID: 8094345

Claim:
An image forming apparatus to generate image data from an original document and to form an image, comprising: a photoelectric conversion unit configured to sequentially convert an image of the original document scanned in a sub-scanning direction into image signals made of a plurality of pixels constituting one line in a main scanning direction; a white reference plate which is white reference for the image signals; a signal determination unit configured to determine that, when a brightness signal outside a given range does not exist in image signals of one line of the white reference plate photoelectrically converted by the photoelectric conversion unit, the image signals of the line are good; a start position specifying unit configured to specify a read start position by detecting at least one acceptance line band which is a portion of the white reference plate in the sub-scanning direction where one or more lines have been determined to be good exist continuously; a white reference signal generation unit configured to generate a white reference signal from image signals obtained by photoelectric converting an image for one or more lines from the read start position of the white reference plate in the sub-scanning direction by the photoelectric conversion unit; and a shading correction unit configured to correct the image signals of the original document image photoelectrically converted by the photoelectric conversion unit, based on the white reference signal; the start position specifying unit specifying an automatic document feeder (ADF) original document read start position which is the read start position for reading an ADF original document within an acceptance line band closest to a position of reading an ADF original document, and specifying a fixed original document read start position which is the read start position for reading a fixed original document within an acceptance line band closest to an original document mounting glass, when a plurality of the acceptance line bands exist.