Image reading device and image reading method for document detection

An image reading method to be performed by an image reading device, the image reading device including:

• a first transport roller configured to transport a document in a predetermined transport direction,
• a second transport roller provided downstream of the first transport roller in the transport direction and configured to transport the document in the transport direction,
• a reading sensor provided downstream of the second transport roller and configured to read the document transported, and
• a document detection sensor provided, in the transport direction, between a position where the first transport roller comes into contact with the document and a position where the second transport roller comes into contact with the document, the document detection sensor being configured to detect the document,
• the document detection sensor being located at a first position, the first position being a position away from an origin of the reading sensor by a first distance in a width direction intersecting the transport direction, the image reading method comprising:
• based on detection of the document by the document detection sensor, starting reading by the reading sensor;
• when a size of the document is not specified, performing first identification processing of identifying, for image data generated as a reading result by the reading sensor and using a search line extending to a downstream end of the image data, a region of the document by detecting an edge of the document from the image data generated as the reading result by the reading sensor;
• and
• when the size of the document is specified, performing second identification processing of searching the image data, at a position within a first range including the first position in the width direction, for a downstream end of the document from the downstream end of the image data toward upstream in the transport direction, and based on a position of the downstream end of the document identified by the searching, identifying as the region of the document a region corresponding to the size of the document specified,
• in the second identification processing, when the searching fails to identify the downstream end of the document from the image data, a control unit identifies a position away from the downstream end of the image data toward upstream by a fixed distance set in advance as a substitute for the downstream end of the document.

An image reading device, comprising:

• a first transport roller configured to transport a document in a predetermined transport direction;
• a second transport roller provided downstream of the first transport roller in the transport direction and configured to transport the document in the transport direction;
• a reading sensor provided downstream of the second transport roller and configured to read the document transported;
• a document detection sensor provided, in the transport direction, between a position where the first transport roller comes into contact with the document and a position where the second transport roller comes into contact with the document, the document detection sensor being configured to detect the document;
• and
• a control unit, wherein
• the document detection sensor is located at a first position, the first position being a position away from an origin of the reading sensor by a first distance in a width direction intersecting the transport direction,
• based on detection of the document by the document detection sensor, the control unit starts reading by the reading sensor,
• when a size of the document is not specified, the control unit performs first identification processing of identifying, for image data generated as a reading result by the reading sensor and using a search line extending to a downstream end of the image data, a region of the document by detecting an edge of the document from the image data generated as the reading result by the reading sensor,
• when the size of the document is specified, the control unit performs second identification processing of searching the image data, at a position within a first range including the first position in the width direction, for a downstream end of the document from the downstream end of the image data toward upstream in the transport direction, and based on a position of the downstream end of the document identified by the searching, identifying as the region of the document a region corresponding to the size of the document specified,
• in the second identification processing,
• setting as the region to be read by the reading sensor in a main scanning direction, a size corresponding to the document specified in the main scanning direction, and
• when the document is inclined, searching for a plurality of downstream ends of the document, identifying, among the downstream ends, the one located farthest downstream as the downstream end of the document, and identifying a region of the document set along the transport direction from the downstream end toward an upstream region.