enhance(1)                                                          enhance(1)



NAME
       enhance - to apply gaussian bandpass filter

SYNOPSIS
       enhance  [input_filename]  [output_filename]

DESCRIPTION
       This is a two-dimensional gaussian bandpass filter program for image
       enhancement purposes.  For three-dimensional images, each image in the
       stack is separately bandpass filtered.  This program is superceded by
       Mtffilter, which provides all of the same filtering capabilities
       plus padding to avoid edge artifacts.

       The filter is specified by four input parameters: Sigma1, Sigma2,
       Radius1, and Radius2.  Several other IMOD programs take these same 4
       parameters, which produce the same effect as described here.  The fil-
       ter functions produced by these parameters can be visualized with the
       program Filterplot.  The filter is the product of two gaussian func-
       tions, the first one typically controlled by Sigma1 and the second one
       by Sigma2, Radius1, and Radius2.  If all values are positive or zero,
       then the first filter is in the form of a gaussian highpass filter
       given by:
            (1. - exp(-r**2/(2*Sigma1**2)))
       The second filter is a gaussian-edged band-pass filter. This filter is
       flat between Radius1 --> Radius2 and decays symmetrically as a gaussian
       below Radius1 or above Radius2:
            exp(-(r-Radius)**2/(2.*sigma2**2))

       If either Sigma = 0, then that part of the filter is removed.

       The units are in fractional reciprocal lattice units, that is r goes
       from 0-->sqrt(2)/2   (0-->.5 on each axis)

       If Sigma1 is negative, the first filter is the second derivative of a
       gaussian, Del-squared G, with formula
            r**2*exp(-r**2/(2.*Sigma1**2))
       This filter alone is bandpass with a peak at 1.414*|Sigma1|, so Sigma2
       and the Radii can be set to zero.

       If Sigma2 is negative, the second filter is inverted (1 minus the Gaus-
       sian band-pass filter).  This filter is then multiplied by the filter
       specified by sigma1 (if any).

       If Radius1 is negative, then the first filter is 0 out to |Radius1| and
       rises as an inverted gaussian from that point:
            (1. - exp(-(r-|Radius1|)**2/(2.*Sigma1**2)))
       The effective Radius1 for the second filter is then 0, but this filter
       can still be used to add lowpass filtering.

       Several modes of operation are possible:

       Gaussian low-pass filter (temperature factor)
             :  Sigma1 & Radii = 0, use Sigma2

       Gaussian bandpass centered at Radius
             :  Sigma1=0,            use Radius1=Radius2 & Sigma2

       Gaussian-edged badpass between Radius1 & Radius2
             :  Sigma1=0,            use Radius1,Radius2 & Sigma2

       Gaussian bandpass (low-pass + high-pass)
             : Radii = 0,            use Sigma1 & Sigma2


       For versions of IMOD distributed or built with FFTW, there are no
       restrictions on the image dimensions.  Otherwise, image dimensions must
       be even and have no prime factors greater than 19.

       The program will accept file names either from the command line or as
       entries to the program after it is started.  If there are two names on
       the command line, they will be taken as the input and output file
       names; if there is one name, it will be taken as the input file name
       and the program will ask for the output file name; if there are no com-
       mand line arguments, the program will ask for both input and output
       file names.

       The output file will have the same mode as the input, and for integer
       data modes, each section will be individually scaled to occupy the
       range for that mode.

       Input parameters are:

       SIGMA1,SIGMA2,RADIUS1,RADIUS2
                             as described above

       IORIG                         if IORIG = 1 then the F(0,0) is
                                     unchanged by filter operation


HISTORY
       Version 1.10    27.MAY.82       DAA             FOR VAX
       Version 1.11    02.JUNE.82      DAA             FOR VAX
       Version 1.12    10.JUNE.82      DAA             FOR VAX
       Version 1.13    23.JULY.82      DAA             FOR VAX
       Update  1.13    18.November.82  DAA             FOR VAX
       Bug fix         14.July.88      DNM             FOR uVAX
       Bit mode        09.August.88    DNM             FOR uVAX
       Del-squared G   01.September.88 DNM             FOR uVAX
       Inverted filter 26.April.89     DNM             FOR uVAX
       Ported to unix  07.December.94  DNM             FOR SGI

BUGS
       Email bug reports to mast at colorado dot edu.



BL3DEMC                              4.7.3                          enhance(1)