In one embodiment, a source mask optimization (SMO) method is provided that includes controlling bright region efficiency during at least one optical domain step. The bright region efficiency being the proportion of the total transmitted light that is transferred to bright areas of a target pattern. The optical domain intermediate solution provided by the at least one optical domain step may then be binarized to obtain an initial spatial domain solution with a controlled MEEF (Mask Error Enhancement Factor). The MEEF is controlled during at least one spatial domain step that optimizes the initial spatial domain solution.