Image reading apparatus and method for generating image data with reference member used for shading correction having a reference surface and background surface at different positions

An image forming apparatus comprising:

• an image reading unit configured to generate reference data by reading a reference surface and to generate image data by reading a sheet;
• a reference plate that includes the reference surface for generating the reference data for shading correction of the image reading unit and a background surface for background of a sheet to be read to generate the image data;
• a control unit configured to control the positions of the image reading unit and the reference plate to be at a first position relative to each other when the reference data is to be generated and at a second position relative to each other when the image data is to be generated, the second position being different from the first position;
• a shading correction unit configured to perform the shading correction in the image reading unit based on the generated reference data;
• and
• an image forming unit that forms an image on a sheet based on the image data generated by the image reading unit after the shading correction.

A method for generating image data comprising the steps of:

• controlling positions of an image reading unit and a reference plate to be at a first position relative to each other, the reference plate having a reference surface and a background surf ace;
• generating reference data by reading the reference plate with the image reading unit when the image reading unit and the reference plate are at the first position relative to each other;
• performing a shading correction in the image reading unit based on the generated reference data;
• controlling the positions of the image reading unit and the reference plate to be at a second position relative to each other, the second position being different from the first position;
• and
• generating image data of a sheet by reading the sheet with the image reading unit subjected to the shading correction when the image reading unit and the reference plate are at the second position relative to each other with the sheet positioned therebetween.