Image reading apparatus and image reading method

An image reading apparatus that optically reads a document, the apparatus comprising:

• multiple line sensors provided approximately parallel to each other and each having light-receiving elements arranged in line form, each line sensor capturing respective line-shaped regions spanning in the main scanning direction of the document in respective color components;
• a movement unit that causes the positional relationship between the document and the multiple line sensors to move relative to the sub scanning direction that is orthogonal to the main scanning direction;
• a storage unit that stores a corrected offset amount, in which an offset amount in the sub scanning direction based on the distance between the multiple line sensors in scan data of each of the color components captured by the multiple line sensors has been corrected, prior to shipping, based on individual error of the optical magnification in the optical system leading from the document to the light-receiving elements;
• a color skew adjustment unit that adjusts positional skew in the sub scanning direction in scan data of each of the color components captured by the multiple line sensors in synchronization with the movement caused by the movement unit, in accordance with the corrected offset amount stored in the storage unit;
• an image generating unit that generates image data expressing the document based on the scan data of each of the color components adjusted by the color skew adjustment unit;
• and
• an offset correction unit that corrects the offset amount used in the adjustment of the scan data based on a magnification change amount, the magnification change amount being the amount of change in the image formation magnification from a design value, an image of the document being formed upon the light-receiving elements, wherein the offset correction unit corrects the offset amount used in the adjustment of the scan data based on the magnification change amount after the image reading apparatus has been started up and before reading the document.

An image reading method for optically reading a document, the method comprising:

• capturing respective color components of respective line-shaped regions spanning in the main scanning direction of the document using multiple line sensors provided approximately parallel to each other and each having light-receiving elements arranged in line form;
• moving the positional relationship between the document and the multiple line sensors relative to the sub scanning direction that is orthogonal to the main scanning direction;
• adjusting color skew in the sub scanning direction in scan data of each of the color components captured by the multiple line sensors in synchronization with the movement carried out in the process of moving, in accordance with an offset amount based on the distance between each of the multiple line sensors;
• generating image data expressing the document based on the scan data of each of the color components adjusted in the process of adjusting;
• and
• correcting the offset amount used in the adjustment of the scan data based on a magnification change amount, the magnification change amount being the amount of change in the image formation magnification from a design value, an image of the document being formed upon the light-receiving elements, wherein correcting the offset amount used in the adjustment of the scan data is based on the magnification change amount after the image reading apparatus has been started up and before reading the document.