INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2020-214839 filed on Dec. 24, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an image processing method and an image processing apparatus for determining a state of an image defect based on a test image.

An image forming apparatus such as a printer or a multifunction peripheral executes a print process to form an image on a sheet. In the print process, an image defect such as a vertical stripe, a horizontal stripe, or a noise point may be generated on the image formed on an output sheet.

For example, in a case where the image forming apparatus executes the print process by an electrophotographic method, the image defect may be caused by any of various parts such as a photoconductor, a charging portion, a developing portion, and a transfer portion. In addition, it requires skill to determine the cause of the image defect.

In addition, there is known an image processing apparatus that preliminarily stores, as table data, correspondence between: phenomena that cause the vertical stripe as an example of the image defect; and feature information such as the color of the vertical stripe, density, and the number of screen lines, wherein a phenomenon that has caused the vertical stripe is identified based on information of the color of an image of the vertical stripe, density, or the number of screen lines in a test image and the table data.

In the table data, the range of a parameter, such as the color of the image, density, or the number of screen lines, is set by thresholds for each type of phenomenon that may cause the vertical stripe.

SUMMARY

In an image processing method according to an aspect of the present disclosure, a processor determines a state of an image defect based on a test image that is obtained through an image reading process performed on an output sheet output from an image forming device. The image processing method includes the processor generating an extraction image by extracting, from the test image, a target specific part that is a horizontal stripe extending in a horizontal direction or a noise point. Furthermore, the image processing method includes the processor deriving, from a target area in the extraction image in which three or more target specific parts are lined up in a vertical direction, a vertical data sequence composed of each representative value of a plurality of pixel values of each line extending in the horizontal direction in the target area. Furthermore, the image processing method includes the processor converting the vertical data sequence to primary conversion data of a frequency domain. Furthermore, the image processing method includes the processor determining whether or not the target specific parts have one or more predetermined periodicities in the vertical direction, based on the primary conversion data. Furthermore, the image processing method includes the processor converting, to secondary conversion data of a space domain, correction data that is obtained by removing, from the primary conversion data, data of frequency bands other than a particular frequency band corresponding to a target specific part that was determined as having the periodicities. Furthermore, the image processing method includes the processor classifying the target specific parts included in the target area into periodic specific part and non-periodic specific part by comparing positions of the target specific parts in the target area with a peak position in a waveform represented by the secondary conversion data, the periodic specific part corresponding to the periodicities, the non-periodic specific part being specific part other than the periodic specific part.

An image processing apparatus according to another aspect of the present disclosure includes the processor that executes processes of the image processing method.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

