An infinite impulse response (IIR) filter provides fast response time without significant effects of ringing or overshoot. In a first step, an input signal is received and a preliminary output signal is computed based upon at least the input signal and a prior output signal. The preliminary output signal is compared to the input signal, and if the preliminary output signal and the input signal differ by more than a significant amount, the input signal is provided as the output signal. Otherwise, the preliminary output signal can be provided as the output signal. Such a filter be readily implemented in software or other programmable logic, and may have particular utility in preserving the contrast in a filtered video image represented by discrete digital data within a display system.