Reading device, image forming apparatus including reading device, and method for controlling reading device

A reading device comprising:

• a document feeder unit including a document tray on which a document sheet is set with a regulation plate for regulating a position of the document sheet, and a detection sensor unit disposed in a document feeding path so as to detect a document size, a document inclination direction, and a document inclination angle in a main scanning direction, so as to feed the set document sheet to a reading position;
• an image reading unit configured to read the document sheet fed by the document feeder unit;
• an operation unit configured to receive an operation for selecting one of a plurality of types of inclination correction modes prepared for inclination correction of read image data of a small width document sheet having a width smaller than a largest width of set document sheets in a document mixed mode in which a plurality of types of document sheets having different sizes are set on the document tray for reading;
• a control unit configured to determine the document inclination direction and the document inclination angle on the basis of an output of the detection sensor unit, and to recognize the document size on the basis of an operation to the operation unit or the output of the detection sensor unit;
• and
• an image processing unit configured to generate the read image data as a result of reading on the basis of image data generated by the image reading unit and the document size determined by the control unit, to perform a process of decreasing inclination by rotating the read image data in a direction opposite to the inclination direction as an inclination correction process, and in the document mixed mode, to rotate the read image data of a largest width document sheet so that the inclination is decreased as the inclination correction process for the largest width document sheet, while to perform the inclination correction process corresponding to the selected inclination correction mode on the read image data of the small width document sheet.