Abstract: An optical proximity correction operation is performed on a layout design, and faults created by the design are identified. If the faults occur where the optical proximity correction was constrained by a mask rule, then the layout design data is edited so that violation of the mask rule is avoided. Once the original layout design has been edited, another optical proximity correction operation is then performed on the edited layout design data. In this subsequent optical proximity correction operation, a simulated image is generated using the edited layout design data, but this simulated image is compared with the target image of the original layout design data rather than the edited layout design data.