https://doi.org/10.1140/epjp/s13360-024-05522-3
Regular Article
A quantitative approach to reflectance transformation imaging in profilometric applications
1
Department of Physics Aldo Pontremoli, Università degli Studi di Milano, Via Celoria 16, 20123, Milano, Italy
2
Arvedi Laboratory of Non-Invasive Diagnostics, CISRiC, University of Pavia, Via Bell’Aspa 3, 26100, Cremona, Italy
3
Department of Musicology and Cultural Heritage, University of Pavia, Corso Garibaldi 178, 26100, Cremona, Italy
4
Istituto di Scienze del Patrimonio Culturale, ISPC-CNR, Via Madonna del Piano 10, 50019, Sesto Fiorentino, FI, Italy
5
Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy
6
INRiM - Istituto Nazionale di Ricerca Metrologica, Str. delle Cacce 91, 10135, Torino, Italy
Received:
30
January
2024
Accepted:
29
July
2024
Published online:
9
September
2024
Reflectance transformation imaging (RTI) is a technique employed to assess both the intensity and directional properties of light reflected from an object, aiming to visualize an object under different incident light directions. This technique has quickly become a commonly used approach for the documentation, acquisition and deciphering for cultural heritage objects, because it enables to enhance and highlight image details. The output of this mathematical synthesis technique, which elaborates illumination information, is contained in a pseudocolour image called normal map. Starting from this image, this technique allows to obtain the reconstruction of the outline of semi-flat objects by integrating the normal map given by the RTI, i.e. normal integration. The technique of normal integration has been known for many years, being widely used in graphical modelling across various fields of 3D imaging. In the context of cultural heritage, this particular form of 3D modelling has already found application in the reconstruction of semi-flat objects, albeit with some limitations in the accurate portraying of low spatial frequencies. However, quantitative and systematic studies on the efficiency of 3D rendering of objects using RTI and normal integration have not yet been conducted. In the context of this research, the quantitative evaluation of the accuracy of the RTI technique with normal integration for profilometric applications on semi-flat objects is proposed and a study on its fidelity in reproducing the considered artefact is conducted. For this purpose, ad hoc profilometric targets were designed, realized and analysed to quantitatively compare the results of RTI and normal integration with different standardized techniques: micro-photogrammetry, laser scanning and optical profilometry.
© The Author(s) 2024
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