Image scanner, method, and computer-readable medium for detecting document edge positions

A method implementable on a processor coupled with an image scanner, the image scanner comprising:

• a document table configured to support a rectangular sheet placed thereon, the document table having a specific position thereon where one of four corners of the sheet is placed as a reference corner;
• and
• an image sensor configured to repeatedly perform line scanning to scan the sheet placed on the document table in a main scanning direction while moving in a sub scanning direction perpendicular to the main scanning direction, thereby generating image data representing a scanned image of the sheet, the method comprising:
• detecting a non-reference corner of the sheet placed on the document table, the non-reference corner being opposed to the reference corner across an upper side of the sheet in the main scanning direction, the upper side extending in the main scanning direction from the reference corner;
• each time the image sensor repeatedly performs the line scanning a predetermined number of times while moving in the sub scanning direction, performing an edge detecting process to detect a position of a lateral side extending in the sub scanning direction from the non-reference corner of the sheet, by detecting a pixel corresponding to the lateral side of the sheet in the main scanning direction within a scanned image corresponding to image data generated by the line scanning repeated the predetermined number of times;
• in the edge detecting process performed for a first time, setting a position of the detected non-reference corner in the main scanning direction as a detection reference position;
• in the edge detecting process performed for a second or later time, setting a previous position of the lateral side in the main scanning direction as the detection reference position, the previous position being a detected position of the lateral side in a previous edge detecting process;
• and
• in each edge detecting process, setting a first detection range in the main scanning direction on the basis of the set detection reference position, and detecting a specific pixel corresponding to the lateral side in the main scanning direction within the first detection range in the main scanning direction.

A non-transitory computer-readable medium storing computer-readable instructions that are executable by a processor coupled with an image scanner, the image scanner comprising:

• a document table configured to support a rectangular sheet placed thereon, the document table having a specific position thereon where one of four corners of the sheet is placed as a reference corner;
• and
• an image sensor configured to repeatedly perform line scanning to scan the sheet placed on the document table in a main scanning direction while moving in a sub scanning direction perpendicular to the main scanning direction, thereby generating image data representing a scanned image of the sheet, the instructions being configured to, when executed by the processor, cause the processor to:
• detect a non-reference corner of the sheet placed on the document table, the non-reference corner being opposed to the reference corner across an upper side of the sheet in the main scanning direction, the upper side extending in the main scanning direction from the reference corner;
• each time the image sensor repeatedly performs the line scanning a predetermined number of times while moving in the sub scanning direction, perform an edge detecting process to detect a position of a lateral side extending in the sub scanning direction from the non-reference corner of the sheet, by detecting a pixel corresponding to the lateral side of the sheet in the main scanning direction within a scanned image corresponding to image data generated by the line scanning repeated the predetermined number of times;
• in the edge detecting process performed for a first time, set a position of the detected non-reference corner in the main scanning direction as a detection reference position;
• in the edge detecting process performed for a second or later time, set a previous position of the lateral side in the main scanning direction as the detection reference position, the previous position being a detected position of the lateral side in a previous edge detecting process;
• and
• in each edge detecting process, set a first detection range in the main scanning direction on the basis of the set detection reference position, and detect a specific pixel corresponding to the lateral side in the main scanning direction within the first detection range in the main scanning direction.