A technique for subtracting images in real time utilizing a single liquid crystal light valve (LCLV) is described. The two images are projected in registration on the LCLV through a common grating. The projections are chosen such that the grating's image due to one beam is complementary to that displayed by the second beam, thus generating an interlacing effect. The readout light beam is optically filtered, so that only different features in the two images are revealed. Experimental results are presented.