Adjacent to the XRD data in Fig. 3, the corresponding XRF sinograms and tomograms are shown. The relatively lowenergetic fluorescence radiation (ETi–Ka = 4.5 keV, EBa–La = 4.4 keV) suffers severely from absorption along the path from within the sample toward the XRF detector. The latter is positioned on the left side (positive x) in the sinograms and at the top in the tomograms. The element-specific intensity of Ti and Ba is therefore observed to gradually reduce with decreasing x (away from the detector), obscuring the rightmost half of the STi–K and SBa–L sinograms of Fig. 3. Thus only the XRF signals that were emitted in the part of the sample closest to the detector during the rotation are visible in the corresponding tomograms gTi–K and gBa–L. For comparison, XRF sinograms and tomograms of Sr–K and Nb–K are also shown in Fig. 3 (third column). 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.