Image reading apparatus, image forming apparatus, and shading correction method

An image forming apparatus comprising:

• an image reading apparatus including:
• a reading unit;
• a first white reference member that is located opposing a document read position of the reading unit and whose read point to be read by the reading unit is changed with time;
• a shading-data generating unit that generates shading data;
• a correction-data generating unit that, when a plurality of documents are continuously conveyed to the reading unit, generates correction data to be used for correcting the shading data in each time period in which the document is not read by the reading unit;
• a shading-data correcting unit that corrects the shading data by using the generated correction data;
• a shading correcting unit that performs, by using the corrected shading data, shading correction on image data of a document that is read by the reading unit after the correction data is generated, wherein
• the correction-data generating unit divides, into a matrix of row blocks in a sub scanning direction and column blocks in a main scanning direction, white data on the first white reference member read by the reading unit during a predetermined time period that is shorter than a time period in which the read point of the first white reference member is returned to a position where the reading unit has started reading the first white reference member, calculates, for each column of the matrix, a correction-data candidate value corresponding to a variation ratio of a mean of data of the row blocks in the sub-scanning direction, and determines a minimum value of the calculated correction-data candidate values as the correction data;
• and
• an image forming apparatus that forms an image by using the image data on which the shading correction has been performed.

A shading correction method performed by an image reading apparatus,

• the image reading apparatus including
• a reading unit;
• and
• a first white reference member that is located in opposing to a document read position of the reading unit, a read point of the first white reference member that is read by the reading unit being changing with time,
• the method comprising:
• generating shading data by shading data generating unit;
• generating, when a plurality of documents are continuously conveyed by the reading unit, correction data in each time period in which the document is not read by the reading unit, the correction data being used for correcting the shading data;
• correcting the shading data by using the generated correction data;
• and
• performing, by using the corrected shading data, shading correction on image data of a document that is read by the reading unit after the correction data is generated, wherein
• the generating the correction data includes dividing, into a matrix of row blocks in a sub scanning direction and column blocks in a main scanning direction, white data on the first white reference member read by the reading unit during a predetermined time period that is shorter than a time period in which the read point of the first white reference member is returned to a position where the reading unit has started reading the first white reference member,
• calculating, for each column of the matrix, a correction-data candidate value corresponding to a variation ratio of a mean of data of the row blocks arranged in the sub-scanning direction, and determining a minimum value of the calculated correction-data candidate values as the correction data.