An image reading apparatus, comprising:
- a platen plate portion on which a document is placed, the platen plate portion being in the form of a transparent plate;
- a contact plate portion that is arranged on a side of the platen plate portion in a first direction, the contact plate portion being in the form of a transparent plate;
- a document transportation apparatus that transports the document along a transportation path that passes on an upper surface of the contact plate portion;
- a scanning unit that includes a light emitter and a light guiding section that are each arranged in a primary scanning direction that intersects the first direction, the scanning unit being movable in a movable region in the first direction and in a second direction opposite to the first direction, the movable region including a region under the platen plate portion and a region under the contact plate portion;
- a primary image sensor that receives light guided by the light guiding section and that outputs a line image signal that represents an amount of light received;
- a unit driving apparatus that moves the scanning unit in the first direction or the second direction in the movable region;
- a data processing section that performs processing on line image data including a plurality of pieces of pixel data and corresponding to the line image signal output by the primary image sensor;
- a first reference portion that is arranged along a side edge that forms an end of the platen plate portion in the primary scanning direction, the first reference portion including a lower surface of a first color;
- a second reference portion that is arranged between the first reference portion and the contact plate portion to be adjacent to the first reference portion in the first direction, the second reference portion including a lower surface of a second color different from the first color;
- and
- an end reference portion that is arranged in an end region of the movable region in the second direction to be adjacent to the first reference portion in the second direction, the end reference portion including a lower surface that includes surfaces of a plurality of specific colors that are aligned in the primary scanning direction, wherein
- the contact plate portion is arranged across a target region and a reference region in the primary scanning direction, the target region being occupied by the platen plate portion, the reference region being occupied by the first reference portion, the second reference portion, and the end reference portion,
- one of the plurality of specific colors is a color different from the first color and the second color,
- the data processing section performs a color determination process to determine whether reference pixel data is data for the first color, data for the second color, or data for the plurality of specific colors, the reference pixel data being a plurality of pieces of pixel data being included in the line image data and corresponding to the reference region, and
- the unit driving apparatus performs drive operations to position the scanning unit at a home position situated between the platen plate portion and the contact plate portion in the movable region, the drive operations performed by the unit driving apparatus being successively selected from a plurality of trial drive operations according to a determination result obtained by the color determination process, the scanning unit being moved a different distance or in a different direction in each of the plurality of trial drive operations.