Patent ID: 9469124
Filing Date: 2016-10-18
CPC Classification: B41J

Claim Text:
1. An image forming apparatus comprising: a first line head comprising a first plurality of nozzles to eject a first ink color; a second line head comprising a second plurality of nozzles to eject a second ink color, the first and second line heads being arranged in a sub-scanning direction, the first and second plurality of nozzles being arranged in a main scanning direction perpendicular to the sub-scanning direction; a single drive circuit configured to drive all of the first plurality of nozzles with a first ejection timing, and to drive all of the second plurality of nozzles with a second ejection timing, the first and second line heads configured to allow the second ink color ejected from the second plurality of nozzles to superimposedly land on the first ink color ejected onto a print sheet conveyed in the sub-scanning direction to form a color image on the print sheet; and a processor configured to: acquire, using a scanner, for each line and for each of the first ink color and the second ink color ejected in the region, a minimum drop number of ink ejected in a region with a color tone change within the color image formed on the print sheet based on image data of the color image; acquire, using the scanner, for each line belonging to the region and for each of the first and second ink colors, a drop number distribution of the first and second ink colors ejected based on the image data; classify, for each line belonging to the region, the first ink color and the second ink color that are to be superimposedly ejected as either a reference color exempted from an ejection timing correction or a correction color subjected to the ejection timing correction, the classification being based on a comparison between the acquired minimum drop numbers of each of the first and second ink colors and a comparison between dispersions of the acquired drop number distributions of the first and second ink colors; acquire, for each line belonging to the region, a correction scheme of the ink ejection timing of the correction color; and correct the ink ejection timing of the correction color in the region with the correction scheme for all pixels on each line.