r494: ctsim.tex

[ctsim.git] / doc / ctsim-concepts.tex

diff --git a/doc/ctsim-concepts.tex b/doc/ctsim-concepts.tex
index 3c6aad14e7cab0310cc82d11f5bbb0d9f43a1801..93e1d4506fdf351c9ebc08cdd8c80fa2b53d57a0 100644 (file)
--- a/doc/ctsim-concepts.tex
+++ b/doc/ctsim-concepts.tex
@@ -260,10 +260,16 @@ in a 16-CPU cluster with good results.
 
 \subsubsection{Filter projections}
 The projections for a single view have their frequency data multipled by
-a filter of absolute(w). \ctsim\ permits four different ways to accomplish this
+a filter of $|w|$. \ctsim\ permits four different ways to accomplish this
 filtering. Two of the methods use convolution of the projection data with the
-inverse fourier transform of absolute(x). The other two methods perform an fourier
-transform of the projection data and multiply that by the absolute(x) filter and
+inverse fourier transform of $|w|$. The other two methods perform an fourier
+transform of the projection data and multiply that by the $|w|$ filter and
 then perform an inverse fourier transform.
 
+Though multiplying by $|w|$ gives the sharpest reconstructions, in practice, superior results are obtained by mutiplying the $|w|$ filter by
+another filter that attenuates the higher frequencies. \ctsim\ has multiple
+filters for this purpose.
+
 \subsubsection{Backprojection of filtered projections}
+Backprojection is the process of ``smearing'' the filtered projections over
+the reconstructing image.
\ No newline at end of file