Vander Lugt (Ref. 1) introduced the use of holograms as frequency plane masks in spatial filtering applications. The technique produces the convolution of an input spatial scene s(x) with a convolving function a(x) by placing a hologram in the Fourier transform plane of a coherent optical processor. The hologram is a photograph of a reference beam and the Fourier trans form- H(f) of a spatial mask function h(x). The filtered scene is realized as an off-axis spatial signal. See Figure 1.