This communication is a reply to certain questions raised on the use of computer image simulation to study grain boundary contrast in field‐ion microscope (FIM) images. The validity of the rigid lattice assumption is assessed for low‐ and high‐angle grain boundaries. Resolution of grain boundary dislocations, boundary contrast as a function of boundary position, the difference in contrast in the FIM between coincidence and off‐coincidence grain boundaries, and the priority of contrast events are discussed. A plane matching method used in transmission electron microscopy is introduced to clarify the relation of bulk boundary structure to surface contrast. The ring‐match model of Page, Howell, and Ralph as it has been applied to our work is evaluated. Suggestions are made as to the proper use of computer image simulation and it is noted that a better approximation to simulation of grain boundary contrast might be achieved by using computer relaxed grain boundary structures as an input for our image simulation program.