Inverse Radon transform

`I = iradon(R,theta)`

`I = iradon(R,theta,interp,filter,frequency_scaling,output_size)`

`[I,H] = iradon(___)`

specifies parameters to use in the inverse Radon transform. You can specify any
combination of the last four arguments. `I`

= iradon(`R`

,`theta`

,`interp`

,`filter`

,`frequency_scaling`

,`output_size`

)`iradon`

uses default
values for arguments that you omit.

`iradon`

assumes that the center of rotation is the center point of
the projections, which is defined as `ceil(size(R,1)/2)`

.

`iradon`

uses the filtered back projection algorithm to perform the
inverse Radon transform. The filter is designed directly in the frequency domain and
then multiplied by the FFT of the projections. The projections are zero-padded to a
power of 2 before filtering to prevent spatial domain aliasing and to speed up the
FFT.

[1] Kak, A. C., and M. Slaney, *Principles of
Computerized Tomographic Imaging*, New York, NY, IEEE Press,
1988.