1. A method of generating a fast mask defect score, the method comprising: performing a first approximated wafer simulation of a defect inspection image to generate an approximated defect wafer image; performing a second approximated wafer simulation of a corresponding reference inspection image to generate an approximated reference wafer image; and computing a defect maximum intensity difference (MID) by subtracting the approximated defect wafer image from the approximated reference wafer image to generate a difference image, computing a centroid of a defect region of the difference image, multiplying the defect region and a Gaussian curve centered on the centroid to generate a product, and integrating the product over the defect region.