Arduino-controlled Reflectance Transformation Imaging to the study of cultural heritage objects
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Arduino‑controlled Reflectance Transformation Imaging to the study of cultural heritage objects Victoria Corregidor1,2 · Renato Dias3 · Norberto Catarino2 · Carlos Cruz2 · Luís C. Alves1 · João Cruz4 Received: 4 March 2020 / Accepted: 16 August 2020 © Springer Nature Switzerland AG 2020
Abstract This article examines the development of a low-cost and portable set-up controlled by an Arduino board to perform Reflectance Transformation Imaging technique, from the information derived from 45 digital photographs of an object acquired using a stationary camera. The set-up consists of 45 high-intensity light emitting diodes (LEDs) distributed over a hemispherical dome of 70 cm in diameter and a digital camera on the top of the dome. The LEDs are controlled by an Arduino board, and the user can individually control the LEDs state (ON or OFF) and duration of illumination. An old manuscript written with iron-gall ink and a set of 1 Euro coins mint in 2002 were photographed with the set-up. The interactive re-lighting and the mathematical enhancement of the object’s surface revealed corrosion, loss of material, scratches and other details, which were not perceived in standard images. These unique features, which can be extracted using edge detection processing, have immediate application in different fields such as cultural heritage or forensic studies, where they can be used as fingerprints to identify unique objects, allowing also recognizing the use of tools to alter the surface of coins to increase the price in the market. Keywords Arduino · Low-cost dome · Reflectance Transformation Imaging · Coins recognition · Degradation visualization
1 Introduction Reflection Transformation Imaging (RTI) technique allows the visualization of the relief of the surface of an object allowing a better representation than the one obtained through a single standard image, since surface self-shadowing or inter-reflections are recorded, enhancing thus the realism of the final image. RTI images offer several advantages when compared to standard images, providing a quick overview of the
texture of an object and enhancing details of the image by a moving virtual light source. Results from RTI technique were very useful to identify morphological changes [1, 2], craquelure, planar distortion, wood grain, canvas weave and pentimenti on several paintings in a museum environment [3]. In this context, when compared with traditional raking light photography, RTI offers several advantages such as the control and knowledge of the exact position and angle of the light and thus the reproducibility of the results.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42452-020-03343-4) contains supplementary material, which is available to authorized users. * Victoria Corregidor, [email protected] | 1Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, E.N. 10 ao km 139,7, 2695‑066 Bobadela LRS, Portugal. 2IPFN, Instituto de Plasmas e Fusã
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