A group of linear spectral transformation for two-dimensional digital filters
José Costa, A. Venetsanopoulos · IEEE Transactions on Acoustics Speech and Signal Processing · 1976
There are eight linear transformations of the spectral plane which map the frequency axes onto themselves. These transformations can be used to change the pass and stop regions of a two-dimensional digital filter. A stable realization is assured by transforming the data rather than the system transfer function.