The emission lines of these two trace constituents are absorbed considerably less because of their higher energy (ESr–Ka = 14.3 keV; ENb–Ka = 19.6 keV) by the paint multilayer. Hence the corresponding sinograms are meaningful and complete, while in the tomograms the presence of these elements is visible throughout the entire length of specific layers. The low net detected Nb–Ka count rate (≤10 cps) causes the niobium distribution maps (both the sinogram as well as the tomogram) to be noisy. Comparison of the Ti- and Ba-related XRF and XRD sinograms and tomograms in Fig. 3 shows in a striking manner the double advantage associated with the use of XRD rather than XRF signals for tomography, that is: (i) XRD-based imaging is more specific since different Ti-bearing phases such as anatase and rutile (both TiO2) will be distinguishable from each other in XRD tomograms but not in the XRF distributions; and (ii) the scattering process exploited by XRD conserves the primary beamenergy (in this case 30 keV) and thereby significantly suppresses the distortions introduced by self-absorption that limit the usefulness of the XRF sinograms and tomograms.