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Filtered Backprojection
We can recognize that the integral in dq (marked in yellow) is
nothing but the sinogram high-pass filtered in Fourier domain,
where the filter is |q|.
With some approximation, the inverse Fourier transform of the
filter is a sync function, which means that, to obtain the original
image, we have to convolve the sinogram with a „edge enhancing“
filter.