METHOD OF CORRECTING THRESHOLD ARRAY, DOT PATTERN DATA STRUCTURE, METHOD OF CORRECTING PIXEL LAYOUT OF IMAGE, AND METHOD OF DETERMINING THRESHOLD ARRAY FOR GENERATING IMAGE

A threshold array having an array of thresholds for reproducing a gradation with a dot pattern as a clustered pattern of dots each made up of one or more blackening pixels is corrected. At least one non-contact point candidate position to be turned into a non-contact point is determined among contact points of the dots. Then, at least one contact point candidate position to be turned into a contact point is determined among non-contact points of the dots at the given gradation. Thereafter, the threshold array is corrected by switching around a threshold for the non-contact point candidate position and a threshold for the contact point candidate position, whereby the layout of contact points of the dots can be corrected.