Additional refined parameters in the basis functions Gc(2θ) are the sample–detector distance and some peak profile parameters (e.g. Gaussian peak widths). The fitted scaling factors are proportional to the amount of scattering material irradiated, and the sinograms Sc(x, ω) give rise to phase distribution maps gc(x, y) in the tomographic plane.
The XRF background spectra B(E) and the diffraction background profiles B(2θ) can be described by means of a sum of orthogonal polynomial terms or subtracted from the original data by means of a peak-stripping algorithm.