Optical Anti-Aliasing Filters

In an electro-optical imager, a readout device (e.g., CCD or vidicon) samples an image discretely. Often the sampling spatial frequency is much less than the Nyquist rate for the system optics. Scene clutter at higher spatial frequencies that the readout passband is aliased into the band, giving excess clutter in the observed image. A number of designs of pupil plane phase-only spatial filters to reduce this excess clutter, while maintaining the system transmittance, are described. The designs include continuous and binary phase filters in rectangular and polar coordinates. Some of the designs give significant reduction in the out-of-band clutter. Keywords: Electrooptical devices, Image processing.