A class of special-purpose processors is described. These processors are for use in holographic imaging systems that utilize electromagnetic waves with radio frequencies. The systems, which operate in very nearly real time, consist of arrays of receiving antennas with a receiver at each antenna. The received intensities control modulation in a second array of antennas that radiate waves generated by a coherent source at a frequency higher than the received waves. The processors are wavefront processors in two senses because they process received wavefronts and because the data flow resembles a wavefront. The processors are data driven so they require no clock, and they operate in parallel. Measurements with a prototype system are described, and a diffraction theory analysis of images is given. Extension to phase receivers and holograms are described, along with a discussion of visible image production in real time.