This example shows how to use radon, iradon, fanbeam, and ifanbeam to form projections from a sample image and then reconstruct the image from the projections. While radon and iradon use a parallel-beam geometry for the projections, fanbeam and ifanbeam use a fan-beam geometry. To compare parallel-beam and fan-beam geometries, the examples below create synthetic projections for each geometry and then use those synthetic projections to reconstruct the original image.
A real-world application that requires image reconstruction is X-ray absorption tomography where projections are formed by measuring the attenuation of radiation that passes through a physical specimen at different angles. The original image can be thought of as a cross section through the specimen in which intensity values represent the density of the specimen. Projections are collected by special medical imaging devices and then an internal image of the specimen is reconstructed using iradon or ifanbeam.
The function iradon reconstructs an image from parallel-beam projections. In parallel-beam geometry, each projection is formed by combining a set of line integrals through an image at a specific angle. The function ifanbeam reconstructs an image from fan-beam projections, which have one emitter and multiple sensors.
See the Image Processing Toolbox™ User's Guide for diagrams that illustrate both geometries.