In this paper, the enhancement of light-induced scattering in congruent SBN:Cr (Sr0.61 Ba0.39 Nb2 O6:Cr) crystals in the presence of an exteally applied electric field and its suppression are studied. If a coherent image is focalized in SBN:Cr crystal without applying exteal electric field, the output image will remain clear, because of the weak photorefractive effect in the crystal. When a field is applied properly along the crystal axis, markedly enhanced scattering from the signal beam and the output image dispersion can be observed due to the increase of the photorefractive twobeam coupling gain and the light-induced index change in SBN:Cr crystals. By introducing a coherent or incoherent beam with higher intensity the light-induced scattering can be suppressed through the erasure of scattering gratings.The difference between coherent and incoherent beam is that the former can also amplify the signal beam as the scattered light is removed, whereas the latter can only make the signal beam revert to its initial state. The results obtained under different experimental conditions are consistent with theoretical analysis.