In this study, we model four atomic filters useful in slow light imaging spectroscopy. We calculate delay using the group velocity in rubidium at 780 nm, mercury at 254 nm, and cesium at 852 nm and 387.6 nm at different temperatures and path lengths of the atomic filter. We also calculate the output of a 5 ns pulse by propagating its Fourier components through cells. Then we compare the results of these two numerical models with the ideal limit set only by the natural linewidth of the atomic transition. This ideal limit corresponds to cases where the frequency is right between two equally strong absorption lines. In this case, delay and transmittance are as high as possible. By tuning the frequency to peaks of transmittance, the filter can work close to ideal. Cesium cell at 387.6, though unable to reach the ideal limit at normal temperatures and path lengths, can still separate this frequency at the cost of less than ideal transmittance.