There are provided an image formation device, method, and program capable of forming an image, which is appropriate for a combination of dot sizes, with high flexibility in design for optimizing halftone processing in a case of using a plurality of dot sizes. Two or more combinations are selected among combinations of a plurality of types of threshold matrix and at least one type of division information for classifying a whole range of threshold values covered by the types of threshold matrix into a plurality of divisions. Then, by respectively applying the two or more combinations, dot sizes of pixels are determined on the basis of assigned two or more code values.