  Here we show how to design phase-shifting algorithms (PSAs) for nonuniform
phase-shifted fringe patterns using their frequency transfer function (FTF).
Assuming that the nonuniform/nonlinear (NL) phase-steps are known, we introduce
the desired zeroes in the FTF to obtain the specific NL-PSA formula. The
advantage of designing NL-PSAs based on their FTF is that one can reject many
distorting harmonics of the fringes. We can also estimate the signal-to-noise
ratio (SNR) for interferograms corrupted by additive white Gaussian noise
(AWGN). Finally, for non-distorted noiseless fringes, the proposed NL-PSA
retrieves the modulating phase error-free, just as standard/linear PSAs do.
