Linearization is a technique to mitigate beam-hardening artifacts in projections and, therefore, the CT slices reconstructed from those projections. Conventional X-ray sources are polychromatic and will produce beam-hardening artifacts if not sufficiently filtered. The Scanner Setup plugin provides a guide to configuring the source, filter, and detector to approximate a monochromatic X-ray source. When beam hardening artifacts persist, linearization provides a way to minimize the artifact and, in some cases, produce correct linear attenuations for the specimen materials.
The linearization process typically uses a least-squares fit to identify a function, usually a polynomial1 that, when applied to the measured attenuations vs thickness, transforms it into a linear function. The plot below shows a typical beam hardened attenuation vs thickness curve for an aluminum specimen(black line), and three possible solutions.