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Digital imaging: the application of shape-from-shading to lace, seals and metal objects

2015; Taylor & Francis; Volume: 38; Issue: 1 Linguagem: Inglês

10.1080/19455224.2014.999004

1945-5232

Rachel Gallen, Dinah Eastop, Eleni Bozia, Angelos Barmpoutis,

Cultural Heritage Materials Analysis

AbstractThis article explores one application of a digital imaging technique to historic objects and online delivery of the virtual object. Shape-from-shading is a computer algorithm used to reconstruct three-dimensional shapes from two-dimensional images. The Digital Epigraphy and Archaeology (DEA) project used shape-from-shading to develop a digital website and toolbox to enhance computer-assisted examination of inscriptions preserved as ektypa. This article reports the results of a project to see if the DEA website and toolbox could be used with other materials and objects with information-rich textured surfaces. Seventeen samples were tested, including lace-like textiles placed on different backing materials; wax seal impressions made from a range of materials; and excavated metals. It was found that image capture with a flatbed scanner achieved better results than a multi-functional printer, and that the unprocessed flatbed scan images were sometimes more informative than digital photographs. It was possible to modify the DEA algorithm for both the lace-like samples and the seal impressions to obtain good three-dimensional (3D) reconstructed images. However, this was not possible with the metal samples due to the nature of the material. The 3D reconstructed images are useful to online users in providing an interactive resource that can be manipulated by the user, rather than a two-dimensional (2D) image.Résumé«L'imagerie numérique: l'application de la technique Shape-From-Shading aux dentelles, aux sceaux et aux objets métalliques»Cet article explore une application d'une technique d'imagerie numérique pour les objets historiques et la mise en ligne de l'objet virtuel. Shape-From-Shading est un algorithme informatique utilisé pour reconstruire une forme tridimensionnelle à partir d'images bidimensionnelles. Le projet Digital Epigraphy and Archaeology (DEA) a employé le Shape-From-Shading pour développer un site Web et une boîte à outils afin d'améliorer l'examen assisté par ordinateur des inscriptions conservées telles que les empreintes. Cet article rapporte les résultats du projet pour déterminer si le site DEA et sa boîte à outils peuvent être utilisés sur d'autres matériaux ou objets ayant des surfaces texturées riches en informations. Dix-sept échantillons ont été testés, à savoir les textiles, comme la dentelle, placés sur différents matériaux de support, les empreintes sur sceaux en cire faites à partir de nombreux matériaux et les métaux archéologiques. Il a été constaté que la capture d'image avec un scanner plat donnait de meilleurs résultats qu'une imprimante multi-fonctionnelle et que les images scannées non transformées étaient parfois plus riches en information que des photographies numériques. Il était possible de modifier l'algorithme DEA pour des échantillons de type dentelle et des empreintes de sceaux afin d'obtenir de bonnes images modélisées en trois dimensions (3D). Toutefois, ce n'était pas possible avec les échantillons de métal en raison de la nature du matériau. Les images modélisées en 3D sont plus utiles aux utilisateurs en ligne qu'une image bidimensionnelle (2D) car elles fournissent une ressource interactive qui peut être manipulée par l'utilisateur.Zusammenfassung„Digital Imaging: Die Anwendung von ‘shape-from-shading' auf Spitze, Siegel und Metallobjekte”Dieser Artikel untersucht eine Anwendungsmöglichkeit einer digitalen Imagingtechnik auf historische Objekte und die Onlineablieferung des virtuellen Objekts. Shape-from-shading ist ein Computeralgorithmus, der eingesetzt wird um eine 3-dimensionale Form aus 2-dimensionalen Bildern zu generieren. Das digitale Epigraphik- und Archäologie Projekt (DEA) nutzt Shape-from-Shading um eine Website und einen digitalen Werkzeugkasten zu entwickeln, um die computergestützte Untersuchung von Inschriften, die als Ektypa erhalten geblieben sind, zu verstärken. Dieser Artikel berichtet von den Ergebnissen eines Projekts, das untersucht ob die DEA Website und Werkzeugkasten auf andere Materialien und Objekte mit informationsreichen Oberflächen angewandt werden kann. 17 Proben wurden getestet; unter anderem spitze-ähnliche Textilien auf verschiedenen Hintergrundmaterialien, Wachssiegelabdrücke aus einer Reihe von Materialien und archäologische Metalle. Es wurde festgestellt, dass ein Flachbettscanner bessere Resultate erzielte als ein Multifunktionsdrucker und dass die unbehandelten Images des Flachbettscanners manchmal mehr Informationen enthielten als digitale Photographien. Es war möglich, den DEA Algorithmus für die Proben aus spitze-ähnlichem Material und Siegelabdrücke zu modifizieren und gute rekonstruierte 3-dimensionale Bilder zu erhalten. Allerdings war das mit den metallenen Proben nicht möglich—dies lag am Material selbst. Die rekonstruierten 3-dimensionalen Bilder sind für online User nützlich, da sie eine interaktive Ressource darstellen, die vom User selbst manipuliert werden kann, anders als 2-dimensionale Bilder.Resumen“La imagen digital: la aplicación de ‘shape-from-shading’ en encajes, sellos y objetos metálicos”Este artículo explora la aplicación de una técnica de imagen digital a los objetos históricos y el despliegue del objeto virtual en 3D. Shape-from-shading es un algoritmo de computadora utilizado para reconstruir la forma tridimensional a partir de imágenes bidimensionales. La Epigrafía digital y el proyecto Arqueología (DEA) utilizan shape-from-shading para desarrollar una web digital y una barra de herramientas que mejore el examen asistido por computadora de inscripciones conservadas como ektypa. Este artículo presenta los resultados de un proyecto para ver si la web de la DEA y la barra de herramientas se podrían utilizar con otros materiales y objetos de superficies texturizadas con abundante información. Se analizaron 17 muestras, incluidos los encajes colocados en diferentes soportes, impresiones de sellos de cera hechos de con variedad de materiales y metales excavados. Se encontró que la captura de imágenes con un escáner de superficie plana logra mejores resultados que una impresora multifuncional, y que las imágenes escaneadas no procesadas proporcionaban, a veces, más información que las fotografías digitales. Era posible modificar el algoritmo DEA tanto para las muestras de encaje como de las impresiones de sellos para obtener buenas imágenes reconstruidas tridimensionalmente (3D). Sin embargo, esto no era posible con las muestras de metal debido a la naturaleza del material. Las imágenes reconstruidas en 3D son útiles para usuarios online, ya que ofrecen un recurso interactivo que puede ser manipulado mejor que en una imagen en dos dimensiones (2D).Keywords: digital imagingdigital preservationshape-from-shadinglace designsseal impressionsmetals AcknowledgementsWe would like to acknowledge the help and support of Nancy Bell, Head of Collection Care, and other colleagues at The National Archives notably Maria Cieslak, Chris Kutler, Jacqueline Moon and John Osbourne.Materials and suppliersCanon 450D SLR digital camera, Canon imagerunner C5030i multi-functional printer:CanonWoodhatchReigateSurrey RH2 8BFUKEpson Expressions 10000XL flatbed scanner:Epson (UK) LtdWestsideLondon RoadHemel HempsteadHertfordshire HP3 9TDUKNotes1 Berthold Horn, Robot Vision (Cambridge, MA: The MIT Press, 1986); Angelos Barmpoutis, Eleni Bozia and Robert Wagman, ‘A Novel Framework for 3D Reconstruction and Analysis of Ancient Inscriptions’, Machine Vision and Applications 21, no. 6 (2010): 989–98.2 Cai Meng, Na Zhou, Xiaoliang Xue and Yang Jia, ‘Homography-based Depth Recovery with Descent Images’, Machine Vision and Applications 24, no. 5 (2013): 1093–106.3 Eleni Bozia, Angelos Barmpoutis and Robert Wagman, ‘Open-Access Epigraphy: Electronic Dissemination of 3D-digitized Archaeological Material’, in Proceedings of the International Conference on Information Technologies for Epigraphy and Digital Cultural Heritage in the Ancient World, Paris, France, September 2014.4 Dinah Eastop, Anna Bűlow and Agnes Brokerhof, ‘Design, Digitisation, Discovery: Enhancing Collection Quality’, Studies in Conservation 57, Supplement 1: IIC Vienna Congress (2012): S96–S102; Dinah Eastop, ‘Taking the Rough with the Smooth: Issues and Solutions for Decorated Surfaces’, in Presenting Rough and Smooth with Innovative Technology: Postprints of the Forum of the Icon Textile Group, held at the V&A on 16 April 2012, edited by A. Fairhurst, 41–8.5 See, for example, Graeme Earl, Kirk Martinez and Tom Malzbender, ‘Archaeological Applications of Polynomial Texture Mapping: Analysis, Conservation and Representation’, Journal of Archaeological Science 37 (2010): 1–11, http://eprints.soton.ac.uk/156253/.6 http://blog.nationalarchives.gov.uk/blog/capturing-and-exploring-texture/ (accessed 21 October 2014); http://blog.nationalarchives.gov.uk/blog/texture-mapping-part-two/ (accessed 21 October 2014); http://blog.nationalarchives.gov.uk/blog/texture-mapping-part-three/ (accessed 21 October 2014); http://blog.nationalarchives.gov.uk/blog/texture-mapping-part-four/ (accessed 21 October 2014); http://blog.nationalarchives.gov.uk/blog/new-light-on-old-seals/ (accessed 21 October 2014).7 A heightmap stored in a bitmap form with 256 discrete equidistant levels of depth can approximate a 3D anaglyph in 9.76 micrometer 3D point accuracy (assuming low reliefs of a typical depth range of 0.5 cm); see Bozia et al., ‘Open-Access Epigraphy'.8 Albedo is the ‘proportion of the incident light or radiation that is reflected by a surface' (Oxford English Dictionary). A white surface will typically reflect more light than a darker surface and therefore has a higher albedo than a darker surface.9 Barmpoutis et al., ‘A Novel Framework for 3D Reconstruction'.10 Barmpoutis et al., ‘A Novel Framework for 3D Reconstruction'.11 The 3D images can be viewed on the Digital Epigraphy website: http://www.digitalepigraphy.org/collection/nationalarchives/ (accessed 21 November 2014).12 If you take a picture of the earth, the side that is not facing the sun appears darker. Based on this observation you can make the following assumption: in an image whatever is dark is not facing the light source, and whatever is bright is facing the light source. This assumption is used in shape-from-shading. So in this case, when the computer finds a bright spot on a seal, it interprets that as being oriented towards the light source. When the computer finds a dark spot on a seal, it interprets that as being oriented in the opposite direction. So the black background areas are interpreted as points with orientation opposite to the direction of light.13 Barmpoutis et al., ‘A Novel Framework for 3D Reconstruction'.14 Karen Thompson and Mike Halliwell, ‘Who Put the Text in Textiles? Deciphering Text Hidden within a 1718 Coverlet: Documentation of Papers Hidden within an Early 18th-century Coverlet using Transmitted Light Photography’, in Textiles and Text: Re-establishing the Links between Archival and Object-based Research, ed. M. Hayward and E. Kramer (London: Archetype, 2007), 237–43; Karen Thompson and Mike Halliwell, ‘An Initial Exploration of the Benefits of using Transmitted Visible Light and Infrared Photography to Access Information Concealed within Multi-layered Textiles’, in Scientific Analysis of Ancient and Historic Textiles, ed. R. Janaway and P. Wyeth (London: Archetype,(2005), 177–84.Additional informationBiographiesRachel Gallen, BA, MA, MSc, has a background in archaeological and preventive conservation. She is currently a trainee preventive conservator on the Heritage Lottery Fund's Skills for the Future programme. This position is split between The National Archives and The Tate, UK. She worked as an intern with Historic Royal Palaces at Hampton Court Palace and at the Petrie Museum of Egyptian Archaeology, UCL. She has volunteered in various museums working on a range of conservation projects. She is particularly interested in new developments and research which will contribute to the field of preventive conservation.Dinah Eastop, PhD, MA, FIIC, ACR, has a background in the history of art, textile conservation and material culture studies and experience of exploiting of digital technology for enhanced access to collections. Her research interests extend from the physical nature of objects to their cultural dynamics. She has been working at The National Archives focussing on enhancing the preservation of, and access to, the Board of Trade Design Register. She is Honorary Senior Lecturer, Institute of Archaeology, University College London, and Visiting Research Fellow at the Universities of Glasgow and Southampton. She co-edited Changing Views of Textile Conservation (2011) with Mary M. Brooks and co-authored Chemical Principles of Textile Conservation (1998) with Agnes Timár-Balázsy. As a result of this project she was invited to join the DEA advisory board. She initiated and leads the Deliberately Concealed Garments Project, see http://www.concealedgarments.org%3cC:/exchweb/bin/redir.asp%3FURL=http:/www.concealedgarments.org/, http://www.textileconservationcentre.co.uk/legacy/dr-dinah-eastop%3chttp:/www.textileconservationcentre.co.uk/legacy/dr-dinah-eastop.Eleni Bozia, BA, MA, PhD, is a Lecturer in the Department of Classics at the University of Florida and a member of the Research Faculty at the Institut für Informatik at the University of Leipzig, Germany. She holds a PhD in Classical Philology from the University of Florida and serves as the Associate Director of the Digital Epigraphy and Archaeology Project at the university, developing open-access scientific tools for the humanities and applying concepts from digital and interactive media to archaeology and classics.Angelos Barmpoutis, BS, MS, PhD, is an Assistant Professor and the coordinator of research and technology in the Digital Worlds Institute, University of Florida. He is also an Affiliate Faculty of the Computer and Information Science and Engineering Department and the Biomedical Engineering Department, University of Florida. His current research interests lie in the areas of machine vision and applications, virtual reality in medicine, human motion capture and analysis using RGB-D cameras, biomedical image processing and visualisation, and facial recognition and expression analysis. He has co-authored numerous highly cited journal publications, conference articles and book chapters, and has received several awards and grants from various funding agencies.