A method of calculating an aerial image of a spatial light modulator array includes calculating pair-wise interference between pixels of the spatial light modulator array; calculating effective graytones corresponding to modulation states of the pixels; and calculating the aerial image based on the pair-wise interference and the effective graytones. The graytones depend only on the modulation states of the pixels. The pair-wise interference depends only on position variables. The position variables are position in an image plane and position in a plane of a source of electromagnetic radiation. The pair-wise interference can be represented by a matrix of functions. The pair-wise interference can be represented by a four dimensional matrix. The effective graytones are approximated using sinc functions, or using polynomial functions.