1. A method for determining an image formed by means including a projection system having an illumination source and a projection lens, wherein a mask is disposed between the illumination source and the projection lens, the method comprising the steps of: providing a source intensity distribution; providing a projection impulse response, said projection impulse response comprising an impulse response of the projection lens; and forming a generalized bilinear kernel comprising an autocorrelation of the source intensity distribution with the projection impulse response.