fourfilter        Apply a Fourier Filter to the Fourier transform

 
                of an image

file format: SPIDER (fourier)

DESCRIPTION: This program can apply a variety of mostly low-pass and
        high-pass filters to 2D and 3D Fourier transforms, that comply 
        with the default standard created by the command "four" 
        (same format as SPIDER-fouriers). 

USAGE:         fourfilter
        
        Fourier Input file: fourier001 
        [Enter input file name]

        Fourier Output file: fourfilter001
        [Enter name for filtered Fourier output file. To obtain the 
        filterd image the invers Fourier transform needs to be calculated
        using "four"]
        
        Filter options:
        .  1, 2 cutoff low-pass and high-pass
        .  3, 4 Gaussian low-pass and high pass
        .  5, 6 Fermi low-pass and high pass
        .  7, 8 Butterworth low-pass and highpass
        .  9    Remez filter
        . 10    B-factor

        Filter type (1-10): 5 
        [Enter the filter type that you want to apply.]

        For cutoff Gaussian and Fermi filter (type 1-6):
           Radius: 0.1
          [Enter radius in absolute Fourier units. If a radius larger than 
          0.5 is entered the program will instead interpret this number as
          Fourier sampling units.]
        
        For Fermi filter (5 and 6):
           Temperature: 0.02
           [Enter Fermi filter temperature factor. 0.02 gives a reasonably
           good ripple suppression. For weak highpass filters (small radius)
           the temperature can be adjusted to 0.01. Otherwise the low
           frequencies may not be sufficiently supressed. The value, however
           should be tuned to the application.]
         
        For Butterworth filter (7 and 8):
            Passband, Stopband: 0.1,0.2
            [Enter the pass-band and stop-band of the filter. The order
            of the filter is derived from these values.]
            
         For Remez filter (9):
            Remez filter file name: remezfilter001
            [Enter the file that contains the remez filter values. For more
            detail see manual of "ff" command in spider.]
         
         For B-factor:
            Cutoff, B-factor, D-constant: 0.5, 1.0, 0.4
            [Enter the frequency cutoff, the B-factor and D, a constant to
            adjust the filtering.for more detail see "ff" command in the
            SPIDER manual]        

REMARKS: This is a standalone version of the Fourier filter in SPIDER. 

Programs: em_fourfilter.py, fourfilter_m.f, (adapted from four1a.f in 
          spider.) ffilts_m.f, (adapted from ffilts.f in spider).
        
Author(s): M. Radermacher, 2012 (.py), 2008 (.f), prior authors: Many.