A technique for determining a full-field Mask Error Enhancement Function (MEEF) associated with a mask pattern for use in a photo-lithographic process is described. In this technique, simulated wafer patterns corresponding to the mask pattern are generated at an image plane in an optical path associated with the photo-lithographic process. Then, the full-field MEEF is determined. This full-field MEEF includes MEEF values in multiple directions at positions along one or more contours that define boundaries of one or more features in the one or more simulated wafer patterns. Moreover, at least one of the MEEF values is at a position on a contour where a critical dimension for a feature associated with the contour is undefined.