FFT Fourier -> Space

Use the 1D FFT > Advanced Settings > FFT Fourier -> Space menu option (FFTOUT GX) to transform from the frequency domain to the space domain.

FFT Fourier -> Space dialog options

Real component channel	Real channel. Script Parameter: FFTOUT.R
Imaginary component channel	Imaginary channel. Script Parameter: FFTOUT.I
Original data reference channel	Original reference space domain channel. Script Parameter: FFTOUT.REF
Output space domain channel	New space domain output channel. Script Parameter: FFTOUT.OUT
DC level multiple	DC (zero wavenumber value) multiple Default is 1.0, i.e. not changed. Script Parameter: FFTOUT.DCMULT

Application Notes

The input real and imaginary channels should have been created from the reference channel using the FFTIN GX. They may also have been derived from channels created by FFTIN.

This method is useful for applying your own filters in the frequency domain. The FFTIN GX can be used to create frequency domain real and imaginary channels. Mathematical algorithms may then be applied to these channels and FFTOUT can be used to convert the result back to the space domain.

Note that a power spectrum can be calculated from the real and imaginary components using the following expression:

 log(r*r + i*i)

Where "r" and "i" are the real and imaginary channels respectively.

The DC level multiple is used for replacing back the trend removed by FFTIN GX. If the DC level is changed after filters, the trend should be replaced back with this multiple. The DC level multiple is default as 1.0, i.e. not changed. However, if some filters are applied to the real and imaginary channels, then this DC level could be changed. In such cases it is the user’s responsibility to provide the value of DC level multiple. For instance, a high pass filter will change the DC level to zero. In such cases the DC level multiple should be 0, the trend will not be replaced back.