Image reading apparatus

An image reading apparatus comprising:

• a transparent plate-shaped platen plate portion on which a document sheet is placed;
• a scanning unit including a light emitting portion and a light guiding portion each disposed along a main scanning direction that intersects a first direction, the scanning unit being movable in the first direction and a second direction opposite to the first direction in a movable area including an area below the platen plate portion;
• a main image sensor configured to receive light guided by the light guiding portion and output a line image signal representing an amount of received light;
• a control device configured to output a direction command signal indicating a moving direction of the scanning unit and a speed command signal indicating a moving speed of the scanning unit;
• a unit drive device configured to move the scanning unit in the movable area in a direction according to the direction command signal at a speed according to the speed command signal;
• a data processing portion configured to process line image data including a plurality of pixel data corresponding to the line image signal output by the main image sensor;
• a first reference portion disposed along a side edge forming one end of the platen plate portion in the main scanning direction and having a lower surface of a first color;
• and
• a second reference portion disposed adjacent to the first reference portion in the first direction and having a lower surface of a second color different from the first color, wherein
• the data processing portion executes a color determination process of determining whether one or more reference pixel data of a reference area corresponding to the first reference portion or the second reference portion in the line image data is data of the first color or the second color,
• the control device positions the scanning unit at a home position on the first direction side with respect to the platen plate portion by sequentially selecting a plurality of drive operations from a plurality of trial drive operations each having a different direction or distance for moving the scanning unit and causing the unit drive device to execute the plurality of drive operations, and
• when causing the unit drive device to execute the plurality of drive operations, the control device outputs, to the unit drive device, the speed command signal of a different level depending on a moving distance of the scanning unit.