## 5 Discussion
V-RTI exhibited Specular Enhancement deficits in the rendering of metallic materials (Figure 16c), a defect inherent in the use of polarized light, which tends to produce an opaque result. Conversely, the ability to fully control the specular reflection is a significant advantage in the final rendering of the model, resulting in a more faithful and useful representation (Figure 16a,b). As illustrated in Figure 15g,h, the normal map generated by the two methods reveals a lack of detail in the V-RTI model, which is a disadvantage when compared to the RTI. Even though there are no other studies in the literature that directly compare RTI and V-RTI outputs, this result could be supported by previous studies in which RTI and 3D scanning have been used for surface evaluation, highlighting the greater performance of RTI [47]. However, despite V-RTI having some limitations in terms of the quality of the output, it can be a powerful tool in cases in which RTI cannot be applied. Eventually, the examination of a wall of the chapel of Ellesiya served as a case study, illustrating the potential of V-RTI generated with a frontal and polarized light. In environments where RTI is unfeasible due to workspace and lighting limitations, V-RTI offers a fresh perspective on objects and surfaces that are otherwise challenging to analyze. The method applied here appears promising in addressing these challenges, although with a trade-off in quality, as photogrammetry offered inferior detail compared to RTI. This approach made it possible to not only gather geological information but also to document all the different human or natural interventions that now characterize the wall relief and that would have been hard to discern without this imaging method (Figure 17). Unlike RTI, V-RTI requires a more complex processing methodology. After the photographic acquisition, the images are prepared for elaboration, which involves several steps and the use of multiple softwares. Furthermore, some 3D modeling knowledge is necessary to ensure control over the entire process, particularly with regard to the design of the virtual dome and the use of animation in Blender. Although these challenges may present an obstacle to the implementation of V-RTI, the possibility of using open-source software (RawTherapee for 2D data, Meshroom for 3D reconstruction, Blender for virtual rendering environment, and Relight for the RTI calculation, among others) enhances the accessibility of this technique. The methodology used in this study, from data collection to its subsequent treatment integrating new image processing methods, has been adapted to the specific conditions of the chapel of Ellesiya. Nevertheless, this approach holds significant potential for future research and can be applied to other types of cultural heritage artifacts. For instance, it can be particularly beneficial in providing new insights into the study of other areas of archaeological interest where the environmental conditions are identical to those of the case study, as well as in other sites where the documentation of fine and shallow engravings involves similar limitations as those found in our study. Additionally, this methodology could be suitable also for applications on very large objects, such as parts of archaeological sites with extensive surfaces, painted walls, frescoes, or ancient cave walls with paintings, in which RTI cannot be applied, but where it would be possible to reconstruct a 3D model, even using drones or digitization techniques, and then apply V-RTI. Furthermore, in future works, V-RTI could be combined with other analytical techniques such as multiband analysis and high-definition imaging, as well as statistical methods for multivariate analysis like Principal Component Analysis (PCA). These combinations can provide valuable metrical data despite modest 3D resolutions, enhancing the analytical capabilities of the methodology.