**rmdc**- remove dc component of the TOS image. Useful when wishing to display the results of a fft.**quad**- create a double sized image from TOS with 4 fold symmetry. This allows fft calculations to be used to give the equivalent DCT manipulations which eliminate boundary effects in processes such as deconvolution.**fft**- compute fast fourier transform of TOS image.**ffti**- compute inverse fast fourier transform of TOS image.**power**- compute power spectrum of TOS fft image.**fgradx**- compute x derivative in the fourier domain of complex TOS image. This method for derivative estimation can sometimes give more accurate estimates than spatial filtering, particularly if a smoothing step is not appropriate.**fgrady**- compute y derivative in the fourier domain of complex TOS image. Other comments as above.