


4. Xray transform of 3

5. Unfiltered Back Projection of 4

6. Reconstruction, i.e., Filtered Back Projection of 4

"Unfiltered back projection" is called "Back Projection"
which is mathematically the dual Xray transform.
"Filtered back projection"
is socalled the reconstruction formula
for the Xray transform mathematically,
that is, the back projection applied by the filter
which is mathematically the square root
of the nonnegative Laplacian on the plane.
