For determining optimum optical proximity corrections (OPCs) for a mask pattern, mask areas are formed on a reticle with each mask area having the mask pattern of polygons that are modified with respective OPCs perturbations. A respective patterned area is fabricated on a semiconductor wafer from each mask area of the reticle. A respective microscopy image of each respective patterned area is generated to determine a respective error function for each mask area by comparing a desired image of the mask pattern and the respective microscopy image. The optimum OPCs are determined as the respective OPCs perturbations corresponding to one of the mask areas having the respective error function that is a minimum of the mask areas.