Abstract: This specification discloses an automatic computer-implemented technique for filtering a two-dimensional array of data in the frequency domain. The program converts the array of numbers by Fourier transformation into the real and imaginary part of the frequency domain. In this domain, undesired waves present in the original array can be completely removed by the elimination from the frequency domain of the components of the Fourier-transformed array which fall within (or, if desired, outside of) a convex polygon of arbitrary shape. The system then re-transforms the remaining data back to the time domain, but the undesired components have been filtered. The program can cause the computer to produce a visual reproduction of the filtered array, or it may simply re-format the data of this array on a tape for further computer processing. Accordingly, this invention permits precision spatial filtering of undesired components from the original array.