The readout visibility of a slit image encoded as a variation of birefringence in a BSO crystal is theoretically and experimentally analyzed. The photorefractive crystal is employed as an optical converter by encoding the incoherent input as modulation of birefringence and then reading it out with linear polarized light. When an analyzer is located in the output, the system behaves like a dynamic intensity filter. The output visibility is presented in terms of the input visibility and for different slit widths. It is established that the output visibility can be strongly or weakly dependent on the input visibility according to how the pass-plane of the analyzer is set.