Parametric image-forming models were used to demonstrate the imaging of potential mask defects over ranges of descriptive parameters, either isolated or coincident with a critical object. Beyond basic defect printability effects, CD errors due to defects near CD objects cause serious constraint on allowable pattern defects or contaminants, and define post-repair requirements. The models can provide scaling laws based on defect type, size, contrast, and proximity to a CD object, as well as rules describing tolerable defects using a threshold value for the local CD anomaly they cause.