Patent ID: 7777918
Filing Date: 2010-08-17
Classification: G03G

Abstract:
1. An image forming apparatus, comprising: a document platen to which a document is set; a white reference member; an exposure lamp to expose the document and the white reference member; a photoelectric conversion element which receives reflected light from the document and the white reference member when the document is exposed by the exposure lamp and the white reference member is exposed by the exposure lamp to output an image signal with a level corresponding to a light receiving quantity; and an image processing unit which has a first processing unit to expose the white reference member by the exposure lamp and to create a white reference value for a shading correction from the output from the photoelectric conversion element at that time, and also has a second processing unit to expose the document by the exposure lamp, to apply a shading correction to the output from the photoelectric conversion element at that time in accordance with the white reference value, and to obtain an image read from the document, wherein the first processing unit comprises: a first control section which performs line scanning an un-scanned area of the white reference member by the exposure from the exposure lamp to obtain a signal corresponding to an image of the white reference member from the photoelectric conversion element; a second control section which stores the output from the photoelectric conversion element in the line scanning in the first control section as a white reference value for the shading correction; a third control section which performs line scanning to an un-scanned area differing from that of by the first control section by the exposure from the exposure lamp; a correction section which applies the shading correction to the output from the photoelectric conversion element in line scanning by the third control section in accordance with the white reference value to obtain an image read from the white reference member; a detection section which detects a similarity degree in a main scanning direction and a similarity degree in a sub-scanning direction of the image read by the correction section; a determining section which determines presence or absence of stripe-like noise in the image read by the correction section from each similarity detected by the detection section; a fourth control section which moves line scanning positions in the first control section to repeat processing by the second section, the third section, the correction section, the detection section, and the determining section when the determination result from the determining section shows the presence of the noise; a storage section which stores a line scanning position by the first control section when the determination result from the determining section shows the absence of the noise as a line scanning position to the white reference member in creating the next white reference value; and a decision section which decides the white reference value, at the time when the determination result from the determining section shows that there is no noise, as a white reference value for a shading correction in reading a document after that time among each white reference value stored by the second control section.