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<H2>pjrec</H2>
Reconstructs the interior of an object from a projection file.<P>
<B>Usage</B><P>

<TT>pjrec projection-filename image-filename image-cols image-rows [options...]</TT><P>
<B>Options</B><P>

<TABLE>


<TR><TD VALIGN=TOP>
<B>Parameter</B>
</FONT></TD>

<TD VALIGN=TOP>
<B>Options</B>
</FONT></TD></TR>


<TR><TD VALIGN=TOP>
- -<TT>filter</TT>
</FONT></TD>

<TD VALIGN=TOP>
Selects which filter to apply to
each projection. To properly reconstruct an image, this filter should
consist of the the absolute value of distance from zero
frequency optionally multiplied by a smoothing filter. The optimal
filters to use are:
<UL>

<LI> <TT>abs_bandlimit</TT>
<LI> <TT>abs_cosine</TT>
<LI> <TT>abs_hamming</TT>
<LI> <TT>abs_hanning</TT>
</UL>


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<TR><TD VALIGN=TOP>
- -<TT>filter-parameter</TT>
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<TD VALIGN=TOP>
Sets the alpha level
for Hamming window.  This parameter adjusts the smoothing of the Hamming
filter and can range from <TT>0</TT> to <TT>1</TT>.
At a setting of <TT>1</TT>, the Hamming filter is the same as the bandlimit filter.
At a setting of <TT>0.54</TT>, the Hamming filter is the same as the Hanning
window.
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<P>

<TR><TD VALIGN=TOP>
- -<TT>filter-method</TT>
</FONT></TD>

<TD VALIGN=TOP>
Selects the filtering
method. For large numbers of detectors, <TT>rfftw</TT> is optimal.
For smaller numbers of detectors, <TT>convolution</TT> might be a
bit faster.
<UL>

<LI> <TT>convolution</TT>
<LI> <TT>fourier</TT> - Uses simple Fourier transform.
<LI> <TT>fourier-table</TT> - Optimizes Fourier transform by precalculating trigometric functions.
<LI> <TT>fftw</TT> - Uses complex-valued Fourier transform with the <EM>fftw</EM> library.
<LI> <TT>rfftw</TT> - Uses optimized real/half-complex Fourier transform.
</UL>


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</TABLE>
<P>

<TABLE>


<TR><TD VALIGN=TOP>
- -<TT>filter-generation</TT>
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<TD VALIGN=TOP>
Selects the filter
generation. With convolution, <TT>direct</TT> is the proper method
to select. With any of the frequency methods,
<TT>inverse-fourier</TT> is the best method.
<UL>

<LI> <TT>direct</TT>
<LI> <TT>inverse-fourier</TT>
</UL>


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<P>

<TR><TD VALIGN=TOP>
- -<TT>interpolation</TT>
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<TD VALIGN=TOP>
Interpolation technique during backprojection.
<TT>cubic</TT> has optimal quality when the
data is smooth. Smooth data is obtained by taking many projections and/or
using a smoothing filter. In the absence of smooth data, <TT>linear</TT> gives better results and
is many times faster than cubic interpolation.<P>
<UL>

<LI> <TT>nearest</TT> - No interpolation, selects nearest point.
<LI> <TT>linear</TT> - Uses fast straight line interpolation.
<LI> <TT>cubic</TT> - Uses cubic interpolating polynomial.
</UL>


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<P>

<TR><TD VALIGN=TOP>
- -<TT>backprojection</TT>
</FONT></TD>

<TD VALIGN=TOP>
Selects the
backprojection technique. A setting of <TT>idiff</TT> is optimal.
<UL>

<LI> <TT>trig</TT> - Use trigometric functions at each image point.
<LI> <TT>table</TT> - Use precalculated trigometric tables.
<LI> <TT>diff</TT> - Use difference method to iterate within image.
<LI> <TT>idiff</TT> - Use integer iteration technique.
</UL>


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<P>

<TR><TD VALIGN=TOP>
- -<TT>zeropad</TT>
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<TD VALIGN=TOP>
Zeropad factor. A setting of
<TT>1</TT> is optimal whereas a zeropad of <TT>0</TT> performs no zero padding.
Settings greater than <TT>1</TT> perform additional zero padding, but without
any significant output difference.
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<P>

</TABLE>


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