The present invention relates to a method of selecting a subset of patterns from a design, to a method of performing source and mask optimization, and to a computer program product for performing the method of selecting a subset of patterns from a design. According to certain aspects, the present invention enables coverage of the full design while lowering the computation cost by intelligently selecting a subset of patterns from a design in which the design or a modification of the design is configured to be imaged onto a substrate via a lithographic process. The method of selecting the subset of patterns from a design includes identifying a set of patterns from the design related to the predefined representation of the design. By selecting the subset of patterns according to the method, the selected subset of patterns constitutes a similar predefined representation of the design as the set of patterns.