A method of generating complementary masks based on a target pattern having features to be imaged on a substrate for use in a multiple-exposure lithographic imaging process is disclosed. The method includes defining an initial H-mask and an initial V-mask corresponding to the target pattern; identifying horizontal critical features in the H-mask and vertical critical features in the V-mask; assigning a first phase shift and a first percentage transmission to the horizontal critical features, which are to be formed in the H-mask; and assigning a second phase shift and a second percentage transmission to the vertical critical features, which are to be formed in the V-mask. The method further includes the step of assigning chrome to all non-critical features in the H-mask and the V-mask.