Image forming apparatus, and method and device for creating dither patterns

Abstract

An aspect of the invention provides an image forming apparatus storing first, second, and third dither pattern groups. The first group contains a plurality of line screens, each associated with one of gray levels in a first range, varying such that as the gray level increases, the line width increases. The second group contains a plurality of void-dot screens, each associated with one of gray levels higher than those in the first range, varying such that as the gray level increases, dots increase to reduce void portions surrounded by the dots. The third group contains, for switching from the line screen to the void-dot screen, a plurality of dither patterns varying such that as the gray level increases from a reference gray level, adjacent lines are connected at joint portions tapered toward tip ends in a manner that a position that gradually advances from the tip ends to basal ends.