Image reading apparatus and method of creating correction data

A method of creating correction data for an image reading apparatus including

• a reading module including reading elements arranged in a direction of arrangement intersecting a direction of transportation of an original copy, and configured to read an image on the original copy transported on a transportation route,
• an illumination unit that illuminates, with light, a reading range to be read by the reading module, and
• a background plate facing the reading elements at a position illuminated with the light, in which
• the reading module, the illumination unit, and the background plate are disposed at positions fixed in the direction of transportation,
• the background plate includes
• a white background portion for shading correction, and
• a black background portion for cutting out the original copy, the black background portion having lower brightness than brightness of the white background portion,
• an area of the black background portion is larger than an area of the white background portion, and
• the white background portion and the black background portion are arranged in the direction of arrangement,
• the method comprising:
• reading the white background portion and the black background portion with the reading module in a state where the original copy is not present, and creating, based on read data of the white background portion and the black background portion being read, correction data used for correcting read data of the original copy;
• and
• after reading the image on the original copy, cutting out, based on the read data of the original copy in the black background portion and based on the correction data, data of the image on the original copy.

A method of creating correction data for an image reading apparatus including

• a reading module including reading elements arranged in a direction of arrangement intersecting a direction of transportation of an original copy, and configured to read an image on the original copy being transported,
• an illumination unit that illuminates, with light, a reading range to be read by the reading module,
• a background plate facing the reading elements at a position illuminated with the light, and
• a storage unit that stores data, in which
• the reading module, the illumination unit, and the background plate are disposed at positions fixed in the direction of transportation,
• the background plate includes
• a white background portion for shading correction, and
• a black background portion for cutting out the original copy, the black background portion having lower brightness than brightness of the white background portion,
• the illumination unit includes
• a light source located on one of outer sides of the reading elements in the direction of arrangement, and
• a light guide that guides the light from the light source to the reading range,
• the white background portion is located at a position more distant from the light source in the direction of arrangement than the black background portion is,
• the storage unit stores
• background plate reference difference data representing a difference between read data of the background plate illuminated with the light on an assumption that the black background portion is the white background portion and read data of the background plate not illuminated with the light, and
• white reference difference data representing a difference between read data of a white reference chart illuminated with the light in a state where the white reference chart is disposed in a range for reading the image and the read data of the background plate not illuminated with the light,
• the method comprising:
• a first step of obtaining black reference read data from the reading module, the black reference read data representing the read data of the background plate not illuminated with the light;
• a second step of obtaining background plate read data from the reading module, the background plate read data representing the read data of the background plate illuminated with the light;
• a third step of obtaining, from the background plate read data, a black background read value at a specific position located closer to an end portion on a white background portion side than to an end portion on a light source side out of two ends in the direction of arrangement of the black background portion, and white background read values at reading positions in the white background portion in the direction of arrangement;
• a fourth step of obtaining, based on the white background read values, a virtual white background read value assumed to be a read value at the specific position on a hypothesis that the specific position is in the white background portion;
• a fifth step of converting, based on a difference between the black background read value and the virtual white background read value, the background plate read data into virtual background plate read data corresponding to read data of the white background portion;
• and
• a sixth step of obtaining, based on a difference between the virtual background plate read data and the black reference read data, based on the background plate reference difference data, and based on the white reference difference data, correction data used for the shading correction.