Images obtained by passive millimeter wave systems are heavily blurred and band-limited due to diffraction. A two-stage superresolution algorithm has been developed to improve their spatial resolution beyond the diffraction limit. Initially, the spectrum of an image is restored within the passband and an interpolation operation may be combined in this stage of processing, but the resulting image then contains strong ringing due to the lack of higher spatial frequencies. These ringing artifacts are then reduced by using a piecewise-linear model which identifies and restores sharp edges, so introducing spatial frequencies beyond the passband. The effectiveness of this method has been demonstrated by applying it to synthesized and real mm-wave images.
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