1. A method of optimizing an illumination pupil shape for a lithographic process, the method comprising the steps of: identifying a target pattern to be imaged by said lithographic process; identifying at least one optimization point in said target pattern; identifying at least one design for manufacturing metric per optimization point; selecting a set of illumination source points based on the identified at least one design for manufacturing metric; and determining the illumination pupil shape based on the selected set of illumination source points.