NAME¶

pjfourier — direct Fourier reconstruction from projections

SYNOPSIS¶

pjfourier pj-file image-file nx ny [OPTIONS]

DESCRIPTION¶

pjfourier reconstructs an image from projection-file by the direct Fourier method: the one-dimensional transform of each projection gives a radial line of the two-dimensional transform of the object (the central slice theorem), those polar samples are resampled onto a Cartesian grid, and an inverse two-dimensional transform produces the image.

Two resampling methods are available. interp interpolates between polar samples; gridding convolves each sample onto an oversampled grid with a Kaiser-Bessel kernel, weights it by the polar sampling density, and deapodizes afterwards. Gridding is the more accurate of the two without zero padding, reaching unpadded roughly what interpolation needs a zeropad factor of 4 to reach; with generous padding the two converge.

Direct Fourier reconstruction is less accurate than the filtered backprojection of pjrec(1), because it interpolates the spectrum on a polar grid; sharp, high-contrast edges fare worst. It is included for comparison and for its speed.

Every tool is run through ctsim-nogui, as in "ctsim-nogui pjfourier ...", or directly if a symbolic link of that name points at it.

The arguments and options are as follows:

pj-file

Name of input projection file

image-file

Name of output image file

--interp

Polar interpolation method