Image forming apparatus in which intermediate gradation reproducibility is enhanced

An electrophotographic image forming apparatus that selects a screen from a plurality of screens corresponding to a plurality of gradation values to form a toner image on media, comprising:

• a storage unit in which a first screen group and a second screen group are stored, the first screen group including a plurality of screens having a first pattern, the first pattern defining a first region including a pixel that is a toner adhesion control target, the second screen group including a plurality of screens having a second pattern, the second pattern defining a second region including a pixel that is not the toner adhesion control target;
• a screen selector for selecting the screen from the first screen group such that the first region expands in a predetermined direction with increasing gradation value, switching the selected screen from the first screen group to the second screen group when the gradation value reaches a predetermined threshold, and selecting the screen, in which a width of the second region in the second pattern is larger than a distance between the adjacent first regions in the first pattern in the predetermined direction, as the screen during switching;
• and
• an image producing unit for performing image formation using the selected screen,
• wherein the screen selector relocates a first portion and a second portion such that the first portion and the second portion are joined by the second region that is not the toner adhesion control target, the first portion including the screen included in the first screen group, the second portion including the screen included in the second screen group, when the first portion and the second portion are adjacent to each other as a result of the selection of the screen in each unit region of the input image.

An electrophotographic image forming apparatus that selects a screen from a plurality of screens corresponding to a plurality of gradation values to form a toner image on media, comprising:

• a storage unit in which a first screen group and a second screen group are stored, the first screen group including a plurality of screens having a first pattern, the first pattern defining a first region including a pixel that is a toner adhesion control target, the second screen group including a plurality of screens having a second pattern, the second pattern defining a second region including a pixel that is not the toner adhesion control target;
• a screen selector for selecting the screen from the second screen group such that the second region expands in a predetermined direction with decreasing gradation value, switching the selected screen from the second screen group to the first screen group when the gradation value reaches a predetermined threshold, and selecting the screen, in which a distance between the adjacent first regions in the first pattern is smaller than a width of the second region in the second pattern in the predetermined direction, as the screen during switching;
• and
• an image producing unit for performing image formation using the selected screen,
• wherein the screen selector relocates a first portion and a second portion such that the first portion and the second portion are joined by the second region that is not the toner adhesion control target, the first portion including the screen included in the first screen group, the second portion including the screen included in the second screen group, when the first portion and the second portion are adjacent to each other as a result of the selection of the screen in each unit region of the input image.