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% @(#)fft_freq.hlq 19.1 (ESO-IPG) 02/25/03 14:03:20
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%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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%.COPYRIGHT (c) 1990 European Southern Observatory
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%.KEYWORDS MIDAS, help files, FFT/FREQUENCY
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%.PURPOSE On-line help file for the command: FFT/FREQUENCY
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%.VERSION 1.0 04-APR-1990 : Creation, KB
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%.VERSION 1.1 26-OCT-1992 : Upgrade, KB
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%----------------------------------------------------------------
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FFT/FREQUENCY 26-OCT-1992 KB
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FFT/FREQUENCY inr ini outr outi
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make discrete Fourier transform with frequency scaling
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Compute the discrete Fourier transform of real or complex frame
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and shift origin of frequency domain to center.
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Transformation, filter.
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FFT/FREQUENCY inr ini outr outi
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inr = frame containing the real part of input frame
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ini = frame containing the imaginary part of input frame;
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if input frame is real, omit parameter `ini' or set it to `?'
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if you enter values for any of the following parameters.
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outr = frame for real part of result transform,
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defaulted to `fftr.bdf'
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outi = frame for imaginary part of result transform,
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defaulted to `ffti.bdf'
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FFT/FINVERSE, FFT/FPOWER, FFT/IMAGE, CREATE/FILTER
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All internal calculations are done in double precision and
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only the final result frames are truncated to single precision.
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To calculate the inverse Fourier transformation use FFT/FINVERSE,
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not FFT/INVERSE which only works for frames obtained with the
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If the number of pixels in an axis of the input frame is not a power
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of 2, the input frame is expanded to the next higher power of 2.
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The result frames will have the original no. of pixels but the
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result frames with expanded size are also kept with names
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`exp_fftr.bdf' and `exp_ffti.bdf'. These frames should be used later
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when calculating the inverse Fourier transform via FFT/FINVERSE!
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The FFT command does NOT work for 3-dim frames.
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Do FFT for image where real part is contained in frame `rr.bdf'
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and imaginary part in frame `ri.bdf'. The real and imaginary parts
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of the FFT are stored in `fftr.bdf' and `ffti.bdf'.
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FFT/FREQU lola ? zr zi
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Do FFT for real frame `lola.bdf' (no imaginary part) and store
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results in `zr.bdf' and `zi.bdf'.