Image scanning apparatus, and method and computer-readable medium therefor

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

• a document table configured to support a document sheet placed thereon;
• a document pressing member having a white document pressing surface;
• and
• an image scanner comprising a light source and a plurality of light receivers arranged in line along a main scanning direction, the image scanner being configured to scan an image of the document sheet placed on the document table while moving along a sub scanning direction perpendicular to the main scanning direction and generate image data of the scanned image, the image data including a plurality of pixels each having a gradation value, the image scanner being further configured to generate a white gradation value by scanning the white document pressing surface of the document pressing member, the method comprising:
• acquiring single-page image data by controlling the image scanner to scan the document sheet placed on the document table and a particular range of the white document pressing surface, the particular range being wider than a size of the document sheet;
• detecting black edge positions by detecting, from the single-page image data, positions of black pixels each having a gradation value less than the white gradation value, each black edge position being a position of a specific one of a leading end and a trailing end of the document sheet in the sub scanning direction;
• determining whether a sheet type of the document sheet is a thin paper or a thick paper, based on the gradation values of the black pixels;
• detecting white edge positions by detecting, from the single-page image data, positions of white pixels each having a gradation value equal to or more than the white gradation value, each white edge position being a position of another specific one of the leading end and the trailing end of the document sheet in the sub scanning direction;
• when determining that the sheet type is the thin paper, detecting, as the white pixels, pixels each having a gradation value equal to or more than a first threshold by determining whether a gradation value of each pixel included in the single-page image data is equal to or more than the first threshold, the first threshold being determined based on the white gradation value;
• and
• when determining that the sheet type is the thick paper, detecting, as the white pixels, pixels each having a gradation value equal to or more than a predetermined second threshold by determining whether the gradation value of each pixel included in the single-page image data is equal to or more than the second threshold.

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

• a document table configured to support a document sheet placed thereon;
• a document pressing member having a white document pressing surface;
• and
• an image scanner comprising a light source and a plurality of light receivers arranged in line along a main scanning direction, the image scanner being configured to scan an image of the document sheet placed on the document table while moving along a sub scanning direction perpendicular to the main scanning direction and generate image data of the scanned image, the image data including a plurality of pixels each having a gradation value, the image scanner being further configured to generate a white gradation value by scanning the white document pressing surface of the document pressing member, the instructions being configured to, when executed by the processor, cause the processor to perform:
• an image data acquiring process to acquire single-page image data by controlling the image scanner to scan the document sheet placed on the document table and a particular range of the white document pressing surface, the particular range being wider than a size of the document sheet;
• a black edge detecting process to detect black edge positions by detecting, from the single-page image data, positions of black pixels each having a gradation value less than the white gradation value, each black edge position being a position of a specific one of a leading end and a trailing end of the document sheet in the sub scanning direction;
• a determining process to determine a sheet type of the document sheet based on the gradation values of the black pixels, the sheet type including a thin paper and a thick paper;
• and
• a white edge detecting process to detect white edge positions by detecting, from the single-page image data, positions of white pixels each having a gradation value equal to or more than the white gradation value, each white edge position being a position of another specific one of the leading end and the trailing end of the document sheet in the sub scanning direction, the white edge detecting process comprising:
• a thin-paper white edge detecting process to, when the sheet type is the thin paper, detect, as the white pixels, pixels each having a gradation value equal to or more than a first threshold by determining whether a gradation value of each pixel included in the single-page image data is equal to or more than the first threshold, the first threshold being determined based on the white gradation value;
• and
• a thick-paper white edge detecting process to, when the sheet type is the thick paper, detect, as the white pixels, pixels each having a gradation value equal to or more than a predetermined second threshold by determining whether the gradation value of each pixel included in the single-page image data is equal to or more than the second threshold.