Fourier and related Functions.

• 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.