A technique was sought to generate signals for imaging systems that would permit the simulation of scenes including unusual environments and system defects. The most valuable simulation would be non-intrusive; i.e., no changes need be made to the system under test; this would permit evaluation of hardware and software using fully operational systems. For example, a simulated nominal scene could be degraded through the addition of simulated clutter; system performance could then be measured when the cluttered scenes were generated. A simulator for this use has been built and demonstrated by General Dynamics. Our current application requirements for such a simulator include relatively high update rate, large, linear dynamic range, very high mechanical and radiometric stability and synchronism with the imaging system. Two key areas of discussion will be the approaches used for gray scale generation and crosstalk mitigation.