Selene Photometric Stereo System

Since 2017, Factum Foundation has been developing a new surface scanning system and workflow designed specifically for the fine surface texture of flat or semi-flat surfaces such as paintings, murals or sculptural bas-reliefs. While the Lucida 3D Scanner still produces the highest level of detail, the Photometric Stereo System has the additional advantage of acquiring both surface information and colour at the same time.

The Selene Stereo Photometric System installed in Oxford © Bodleian Libraries

© Matt Marshall

The Selene photometric stereo system (SPSS) is the latest non-contact and ultra high-resolution 3D and colour recording system and workflow. It is designed specifically to record the surface texture of flat or semi-flat surfaces such as paintings, murals, manuscripts, books, book bindings, prints, copperplates or palm leaf manuscripts, capturing details and information invisible to the human eye. This system merges non-contact 3D recording technologies, depth maps, albedo colour, GIS with image stitching software, lighting and CNC software.

The Selene is the culmination of more than 25 years of research into surface recording and 3D capture by Factum Foundation. The system is based on the photometric stereo technique, which captures 2D images under different directional lighting and extracts ultra-high-resolution information about the surface of an object. This is achieved by four synchronised f lashes linked through a custom electronic board to a mirrorless camera. The multiple light sources and advanced algorithms calculate surface normals and highlight fine details, such as brushstrokes, relief, or surface imperfections.

Until the advent of Selene PSS, material culture (paintings, textiles, works on paper, etc.), though rich in threedimensional details and textures, was reduced to a twodimensional representation. However, Selene PSS has radically transformed this approach. The system captures both colour and 3D surface concurrently – a marriage of dimensions and aesthetics. By combining surface relief capture with colour, details that previously went unnoticed are unveiled. From subtle marks without pigmentation to barely perceptible drawings on engraving plates, Selene PSS is pushing the boundaries of knowledge in the realm of research and conservation.

The objectives of the Selene:
•To capture the colour texture of a surface with a resolution of up to 254 dpi and 16 bits
•To capture depth resolution of up to 0.1 mm
•To make the recording process as efficient as possible
•To scan large surfaces

The Selene motorised unit is adaptable, agile and userfriendly and the camera position can be adjusted over an object as each shot gathers information from a rectangular area measuring 20 x 14 cm. At maximum resolution (1000 dpi), the capture distance is approximately 40 cm. The standard system uses a 45-megapixel camera in combination with a 50mm lens. The combination of advanced camera technology and precise optics results in highly detailed and accurate scans suitable for various applications. At the centre of the Selene’s design was a uniquely simple ambition: to digitise surfaces with an unparalleled level of detail. Eight different pieces of software are employed in post-processing in order to achieve the high-resolution derivatives.

In our mission to document surfaces with unparalleled precision, we lean on the foundations of geographic science, merging the domains of artistic documentation and spatial mapping. Selene’s workflows are powered by Geographic Information Systems (GIS) software, the same platforms cartographers employ to chart the world.

First recording tests with the ‘standard board’. It contains types of surfaces that commercial 3D scanning systems find difficult to capture © Otto Lowe for Factum Foundation

Abhijit Dhanda working on the first prototype scanner © Otto Lowe for Factum Foundation

Enrique Esteban working on the photometric scanner © Otto Lowe for Factum Foundation

The second prototype © Oak Taylor-Smith for Factum Arte

Jorge Cano working on the second prototype © Oak Taylor-Smith for Factum Arte

In January 2022, a Selene system was installed at the Bodleian Libraries alongside the Lucida 3D scanner at the ARCHiOx studio (Analysis and Recording of Cultural Heritage in Oxford) in the Bodleian Library. The aim was to use this technology to contribute to the study, conservation and dissemination of key items in the Library’s collections. All the work at the Bodleian Libraries has been carried out by John Barrett, Senior Photographer and ARCHiOx Technical Lead for the Bodleian, with support from Factum’s Jorge Cano, Carlos Bayod, Celeste Anstruther and Adam Lowe. The work at ARCHiOx, including and especially the implementation of the Selene system, has been supported by the Helen Hamlyn Trust.

The work with the Selene Photometric Stereo System was the first time a 3D scanning technology had been systematically integrated into the Bodleian’s workf low, offering a new way to access and interact with the unique items in their collections. This project has demonstrated that 3D surface recording can create new possibilities for how libraries handle and preserve their collections. By customising and adapting the International Image Interoperability Framework (IIIF) for 3D integration, the Bodleian is paving the way for a more immersive and engaging experience for researchers, educators, and other users worldwide.

Beyond academic and conservation discoveries, this technology has had an unexpected cultural impact: revitalising public interest in collections that were accumulating dust in storage and heading to oblivion. A tangible example of this renaissance is the Rawlinson Copperplates collection, which was digitised by John Barret within the framework of the ARCHiOx project with researcher Chiara Betti. The 3D recording of one of the plates revealed a piece of music (notes and text) inspired by verses 1-2 of Psalm 9.

In the Selene PSS, light and illumination is not merely a tool to create ever more detailed images, but a means to deeper revelation and understanding. Through the interplay of light and shadow (Shape from Shading SfS technique), the Selene succeeds in capturing and reproducing surfaces with a fidelity and detail that goes beyond mere visualisation, merging cartography, history, and science into a high-quality 3D scanning system.

Tests over a copper plate © Factum Arte

Lucida 3D Scanner test © Factum Arte

Selene Photometric Scanner test © Factum Arte

Detail comparison of surface information and colour acquired by Selene © Factum Arte

Colour information on a test painting © Factum Arte

Shaded render of the surface of the test painting © Factum Arte

Colour information on a test copper plate from the Bodleian Libraries © Factum Arte

Shaded render of the surface of a copper plate © Factum Arte

Colour information on a test copper plate from the Bodleian Libraries © Factum Arte

Shaded render of the surface of a copper plate © Factum Arte

Test on one of the Sanskrit palm leaf manuscript from the Bodleian Libraries © Factum Arte

Shaded render of the surface of a Sanskrit palm leaf manuscript from the Bodleian Libraries © Factum Arte

For more information about our new technologies for cultural heritage digitisation contact
Team: The project was conceptualised and driven by Jorge Cano, with contributions from Carlos San Juan from the R&D Department at Factum Foundation.
Abhijit Dhanda and Adam Weigert at the Carleton Immersive Media Studio (CIMS) at Carleton University, Canada also made significant contributions to the development of the system. The Carleton side of the project received funding from the NSERC Create Heritage Engineering and New Paradigms New Tools grants. Earlier iterations benefited from the input of Enrique Esteban and Matt Marshall.