We analyzed the phase conjugate reflectivity by photorefractive four-wave mixing exposed to incoherent erasure, and found that the incoherent erasure brings inversion relation in amplitude of the phase conjugate beam with the intensity of the erasure even in a large coupling photorefractive material. Since such inversion relation appears in real-time, this function contributes to put forward holographic filtering to real-time processing. For the sake of confirmation of the analysis, we performed an experiment with employing a 45^{\circ} -cut \hbox{BaTiO}_3 crystal which is known as a crystal providing one of the largest photorefractive beam coupling.