7.1.62. 3dDFT

Link to classic view

++ Authored by: Kevin Murphy & Zhark the Transformer Usage: 3dDFT [options] dataset

where ‘dataset’ is complex- or float-valued.
  • Carries out the DFT along the time axis.
  • To do the DFT along the spatial axes, use program 3dFFT.
  • The input dataset can be complex-valued or float-valued. If it is any other data type, it will be converted to floats before processing.

OPTIONS:

-abs == output float dataset = abs(DFT)
  • Otherwise, the output file is complex-valued. You can then use 3dcalc to extract the real part, the imaginary part, the phase, etc.; see its ‘-cx2r’ option:

    3dcalc -cx2r REAL -a cxset+orig-expr a -prefix rset+orig

  • Please note that if you view a complex dataset in AFNI, the default operation is that you are looking at the absolute value of the dataset.

++ You can control the way a complex IMAGE appears via
the ‘Disp’ control panel (ABS, PHASE, REAL, IMAGE).
++ You can control the way a complex TIME SERIES graph appears
via environment variable AFNI_GRAPH_CX2R (in ‘EditEnv’).
-nfft N == use ‘N’ for DFT length (must be >= #time points)
-detrend == least-squares remove linear drift before DFT
[for more intricate detrending, use 3dDetrend first]
-taper f == taper ‘f’ fraction of data at ends (0 <= f <= 1).
[Hamming ‘raised cosine’ taper of f/2 of the ] [data length at each end; default is no taper] [cf. 3dPeriodogam -help for tapering details!]
-inverse == Do the inverse DFT:
SUM{ data[j] * exp(+2*PI*i*j/nfft) } * 1/nfft
instead of the forward transform
SUM{ data[j] * exp(-2*PI*i*j/nfft) }

++ Compile date = Dec 16 2015

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