1. A computer-implemented method of simulating imaging performance of a lithographic process utilized to image a target design having a plurality of features, said method comprising: determining, using a computer, a function for generating a simulated image, said function having one or more variables accounting for process window variations from a nominal process condition associated with said lithographic process; and generating, using the computer, said simulated image utilizing said function; said simulated image representing an imaging result of said target design for said lithographic process.