Image processing device, image forming apparatus, image processing method, and non-transitory recording medium

An image processing method comprising:

• first detecting contamination on an image reading device using a first relative threshold value calculated from a standard deviation of pixel values of a same-density region in a read image obtained by the image reading device, the image reading device reading a reference image formed on a recording medium by a line head including a plurality of inkjet heads and that has density regions of a plurality of gradations;
• second detecting contamination on the image reading device using a second relative threshold value calculated from a standard deviation of pixel values of an area in the read image, the area being divided for each of the plurality of inkjet heads;
• and
• eliminating an influence of the contamination on the read image when at least one of the first detecting or the second detecting determines the contamination.

A non-transitory recording medium storing a plurality of instructions which, when executed by one or more processors, causes the processors to perform an image processing method, the method comprising:

• first detecting contamination on an image reading device using a first relative threshold value calculated from a standard deviation of pixel values of a same-density region in a read image obtained by the image reading device, the image reading device reading a reference image formed on a recording medium by a line head including a plurality of inkjet heads and that has density regions of a plurality of gradations;
• second detecting contamination on the image reading device using a second relative threshold value calculated from a standard deviation of pixel values of an area in the read image, the area being divided for each of the plurality of inkjet heads;
• and
• eliminating an influence of the contamination on the read image when at least one of the first detecting or the second detecting determines the contamination.