Document reading device, image processing device, document reading method and recording medium

A document reading method executed in a document reading device comprising:

• a hardware processor;
• a conveying roller that conveys a document;
• a background member that is provided in a direction traversing a document conveyance direction and has a mark for correcting an inclination of the document;
• a color reader that reads an image of the document conveyed by the conveying roller and outputs color image data to the hardware processor;
• and a monochrome reader that reads the image of the document conveyed by the conveying roller and outputs monochrome image data to the hardware processor, the method comprising:
• switching, by the hardware processor, a state of the document reading device into a first state in which the image of the document can be read by the color reader and the mark of the background member can be read by the monochrome reader at a time of a color mode to read the image of the document by the color reader and read the mark of the background member at a time of passage of the document by the monochrome reader, and switching, by the hardware processor, the state of the document reading device into a second state in which the image of the document can be read by the monochrome reader and the mark of the background member can be read by the color reader at a time of a monochrome mode to read the image of the document by the monochrome reader and the mark of the background member at the time of passage of the document by the color reader;
• detecting, by the hardware processor, the inclination of the document based on a reading result of the mark of the background member at the time of passage of the document by the color reader or the monochrome reader;
• and
• correcting, by the hardware processor, the inclination of the color image data output from the color reader at the time of the color mode, and correcting the inclination of the monochrome image data output from the monochrome reader at the time of the monochrome mode, in accordance with the inclination of the document detected by the detecting.