Image reading apparatus

An image reading apparatus comprising:

• a platen for a document to be placed thereon;
• a reading unit configured to be conveyed along the platen and to read the document;
• a partial pre-scanning device configured to convey the reading unit in an edge detection area and causes the reading unit to execute a reading operation in the edge detection area, the edge detection area being a partial area within a scannable area on the platen, the scannable area being for the reading unit to be capable of reading;
• a detecting device configured to detect a plurality of edge pixels on a basis of image data, the plurality of edge pixels representing a side of the document, the image data being outputted by the reading unit that reads the edge detection area through execution of the reading operation by the partial pre-scanning device;
• and
• a determining device configured to determine a size of the document on a basis of the plurality of edge pixels detected by the detecting device,
• wherein upon the plurality of edge pixels not detected on the basis of the image data by the detecting device, the partial pre-scanning device moves the edge detection area in a conveying direction of the reading unit and causes the reading unit to execute the reading operation.