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.TH filterplot 1 4.6.34 IMOD
.SH NAME
filterplot - plot filter created by 4 IMOD filter parameters
.SH SYNOPSIS
filterplot [graph options]
.SH DESCRIPTION
Filterplot shows a graph of the filter function created by the four
parameters that are used in many IMOD programs: Sigma1, Sigma2, Radius1,
and Radius2. After you start the program, simply enter the parameters
to see the graph of the filter attenuation factor versus spatial frequency.
Frequency is in reciprocal pixels and ranges from 0 to 0.5 in the graph,
although the filter function does extend farther than 0.5 to cover the
higher frequencies found at oblique angles in 2D images and 3D volumes.
.P
The filter is the product of two gaussian functions, 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)))
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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))
.P
If either Sigma = 0, then that part of the filter is removed.
.P
The units are in fractional reciprocal lattice units,
that is r goes from 0-->sqrt(2)/2 (0-->.5 on each axis)
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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))
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This filter alone is bandpass with a peak at 1.414*|Sigma1|, so Sigma2 and
the Radii can be set to zero.
.P
If Sigma2 is negative, the second filter is inverted (1 minus the Gaussian
band-pass filter). This filter is then multiplied by the filter specified
by sigma1 (if any).
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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)))
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The effective Radius1 for the second filter is then 0, but this filter can
still be used to add lowpass filtering.
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Several modes of operation are possible:
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Gaussian low-pass filter (temperature factor)
: Sigma1 & Radii = 0, use Sigma2
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Gaussian bandpass centered at Radius
: Sigma1=0, use Radius1=Radius2 & Sigma2
.P
Gaussian-edged badpass between Radius1 & Radius2
: Sigma1=0, use Radius1,Radius2 & Sigma2
.P
Gaussian bandpass (low-pass + high-pass)
: Radii = 0, use Sigma1 & Sigma2
.SH HISTORY
.nf
Added to package, 6/19/08
.fi
.P
Filterplot takes several standard command-line options about the graphics
window: \fB-s\fR followed by a window size in x and y, \fB-p\fR
followed by a window position in x and y, \fB-message\fR followed by a
message to be shown in a message box, \fB-tooltip\fR followed by a
tooltip for the graphics window, and \fB-nograph\fR to disable the
graphics window.
.SH BUGS
Email bug reports to mast@colorado.edu.