A photo-essay by the Bodleian’s Senior Photographer and ARCHiOx Technical Lead for the Bodleian, John Barrett
Producing objectively accurate images from the books and manuscripts in the Bodleian’s collections to enrich our growing digital archive is the primary focus of the Imaging Services department. On occasion, requests from curators or clients may require our photographers to use specialist imaging techniques such as recording originals using ultra-violet light or infrared cameras. However, for the most part the aim is not to reveal hidden details, but to produce faithful digital reproductions.
In contrast, the aim of a new research and development project now underway in the Bodleian’s Imaging Studio is to record items from the collections in three dimensions, using entirely new technology, in the expectation that discoveries will be made through recording surface detail at extremely high resolution.
ARCHiOx –Analysis and Recording of Cultural Heritage in Oxford–is a collaborative project, bringing together the Bodleian Libraries and the Factum Foundation. Based in Madrid, the Factum Foundation specialise in high-resolution 3D imaging and have worked in cultural heritage institutions throughout the world, producing exceptional, three-dimensional facsimiles of artworks and artefacts.
During this one-year project, experts from the Factum Foundation will provide equipment and training in the use of new technologies and assist in exploring ways in which the output from the project can surfaced in Digital Bodleian. As the project progresses it is hoped that through the collaboration between technicians at the Bodleian and the Factum Foundation, solutions to improve and streamline the technology will be identified.
With generous funding support from the Helen Hamlyn Trust, the ARCHiOx project will continue until January 2023. Thereafter the technology will remain at the Bodleian making it possible to provide high-resolution 3D capture as an ongoing service.
Unlike perhaps more widely-known 3D capture techniques such as photogrammetry, the two state-of-the-art machines used for ARCHiOx use different principles for recording volume and are specifically designed for the capture of low-relief surface texture. This makes them well suited to the recording of the primarily flat, but texturally rich originals from the Bodleian’s collections. This high-resolution, low-relief capture has been termed ‘2.5D’ rather than 3D.
The 2.5D data produced during the project will serve two purposes. Shaded renders make it possible to view the surface texture of an original while removing their visible tone and colour. This allows for academic research from originals that contain textural details which are difficult to see and cannot be adequately recorded using traditional photographic techniques. Alternatively, the data may be used to produce 3D facsimiles from items within our collections, allowing the material nature of the original to be reproduced.
The Selene is an entirely new solution for capturing 2.5D data and is being used for the first time in the Bodleian. Using computational methods to extract very detailed information about the surface of an object, the Selene records multiple 2D source images, each captured with meticulously positioned lighting. The Selene was designed by Factum Foundation engineer, Jorge Cano and uses a principle called photometric stereo. Captures generated with the Selene during the last two months have proved that the technology is capable of recording surface relief at an incredible 25 microns, or 0.025mm. This is over three times the resolution of any technology previously used to capture cultural heritage material by the Factum Foundation.
Taking two weeks to build and refine, the Selene was installed by designer Jorge Cano and engineer Matt Marshall in the Bodleian’s Imaging studio, in early February. The Selene uses a high resolution camera and four custom flash units, which together can be moved horizontally over the surface of the original. Multiple customised electronic modules synchronise the movement of the motorised guides with the triggering of each sequence of flashes. The Selene captures a series of image tiles at a resolution of 1040 pixels-per-inch. The number of tiles, which is dependent on the size of the original can be programmed allowing for fast, automated capture.
Unlike the laser recording system which has been used successfully for over a decade by the Factum Foundation, the Selene not only generates surface data, but can also capture colour. This is hugely beneficial as not only does it make it unnecessary to capture the original twice but, due to being produced using the same source images, the shaded render showing surface texture and the colour image, known as the albedo, can be aligned perfectly to easily create a composite from the two. We believe this composite image can be of great value to researchers, containing an exceptional level of detail and a real sense of the material nature of the original.
Created from multiple source images, each lit from different angles, the albedo is an exceptionally evenly illuminated and shadowless recording. In some cases the albedo has a notable advantage over images produced using traditional lighting methods, which for 2D capture typically require just two primary light sources. For originals with an uneven and highly reflective texture such as varnished paintings, creating an albedo may offer an effective solution for reducing unwanted highlights in reproductions.
Employing a very different principle to the Selene, the Lucida is a close-range, non-contact recording system that captures high-resolution surface texture data through the use of a laser and two tiny cameras. This is a well-established solution for 2.5D capture, having been used by the Factum Foundation since 2011 during projects including the recording of the Tomb of Seti I, in Egypt. The Lucida is capable of scanning taller originals, or those with greater vertical variation than the Selene and has been used extensively to produce data suitable for the manufacture of remarkably accurate 3D facsimiles. Height data captured with the Lucida is incredibly accurate, though the resolution of the Lucida is significantly lower than the Selene in all three dimensions.
The Lucida was installed at the Bodleian’s imaging studio by Factum Foundation expert Carlos Bayod Lucini. The data generated from the Lucida has been vital in two ways. Comparing data between the two technologies has made it possible to determine an accurate elevation factor, allowing height measurements to be correctly estimated and recorded for depth maps produced with the Selene. Through combining the two data sets by overlaying the high frequency information generated with the Selene, and the more reliably recorded gentle, but taller gradients measured with the Lucida, it has also allowed for the production an incredibly accurate depth map, using the combined strengths of the two recording systems. This technically ambitious process is an important achievement in 2.5D capture and will make it possible to create 3D reproductions at higher resolution and with more accuracy than previously achieved by the Factum Foundation.
A selection of 18th–century copper printing plates are amongst the first of the Bodleian’s originals to be captured with the Selene and Lucida. Primarily from the Rawlinson collection, the plates include portraits of antiquarian Anthony Wood and 17th century Archbishop William Laud, as well as scenes, architecture and antiquities. Plates from the Lister and Gough collections, the latter featuring portraits made from drawings attributed to William Blake, have also been recorded for the project. Perfect for 2.5D capture using photometric stereo technology, copper printing plates have relatively flat surfaces and very shallow, highly detailed engraved lines. The notable plates chosen for capture were selected by Co-ordinator of the Centre for the Study of the Book, Dr Alexandra Franklin and Chiara Betti, a PhD student at the University of London specialising in the research of the Bodleian copper plate collections on a Collaborative Doctoral Partnership, with advice from researchers who have worked on the Bodleian’s rare collections of copper plates and the associated publications. As well as recording each plate’s text and illustrations, it is hoped that images produced during the project will reveal evidence of corrections, alterations, and degradation through use.
Notoriously difficult to capture using traditional photographic techniques, copper printing plates provide a number of challenges for the photographer hoping to record their surface. There is little consistency in the material nature of the copper plates in our collections. While some plates have been cleaned and are highly reflective with little change to their original colour and lustre, others, still bearing corrosion on their surfaces, reflect back virtually nothing and when reproduced, images may lack tonal variation and detail.
When photographing flat metal objects, the risk of capturing the reflections of the photographic equipment and the necessity to position the primary light source extremely close to the lens typically mean that a case-by-case approach is required. This is a very different methodology when compared to the recording of paper and parchment originals, where a consistent workflow and continuous measurement is essential.
Using the Selene as an alternative to traditional photography has proven extremely successful, allowing us to record at a level of detail never previously achieved, and without having to navigate the complications previously associated with capturing metallic originals.
Though capture of the source images using the Selene Photometric Scanner is relatively fast, currently the workflow required for processing the images is slow and reasonably complicated. A number of software applications are required to generate the final derivative images, and one of the goals for ARCHiOx is to develop a more streamlined process.
Producing a normal map is the initial step in the process of creating useful derivatives such as shaded renders. Normal maps are commonly used in CGI and computer game design. Though the normal map is a 2D image, 3D information can be derived from the normal map because instead of simply recording a colour, each pixel represents a direction relative to the recorded surface of an original. An entirely flat surface positioned parallel to the camera would be recorded on the normal map as a line, perpendicular to the original. As the angle of the surface of the original changes, so too do the angles of the recorded lines, known as normal vectors. Recording these normal vectors pixel-by-pixel makes it possible to map the surface of the original. The direction of the normal vectors are defined by each pixel’s red, green and blue content. Given that a copper printing plate is almost flat, the normal map represents the surface with an almost uniform purple colour.
Using the normal vectors from the normal map, a depth map can be generated. This two-dimensional greyscale image uses tonal range to store elevation values. It is processed at 16bits which allows for far more increments between tones to be recorded than in a standard 8bit image. Through applying a Gaussian blur to the depth map, a derivative which records the gentle gradients over a wider area of an original can also be made. In the workflow which has been established for the project, it is from the depth map that shaded renders can be created, using mapping software.
In ordinary use, a geographic information system, or GIS application, can be used to create topographic maps and 3D visualisations of landscapes using aerial imagery. By greatly increasing the scale factor, the same software can be used to map the tiny variations captured with the Selene and Lucida. The light direction and intensity can be configured, processing the depth map in to a highly detailed shaded view of the surface of the original. This shaded render can then be exported as a 2D image.
Though shaded renders provide an exceptional visualisation of the texture of an original, allowing researchers to virtually relight shaded renders for themselves is extremely useful as changes in the direction and height of the light can reveal details which may be hidden when recorded in a single shaded image. In the case of the copper plates, engraved lines will either appear darker or lighter depending on the direction and height of the light. As well as developing viewers capable of displaying and merging image layers produced during the project, Richard Allen, Andy Irving and Tim Dungate from the Bodleian Digital Library Systems and Services hope to develop tools that will permit this virtual relighting from the derivatives created from the 2.5D recording systems.
One of the most important elements in developing the Selene is to establish an accurate elevation scale factor. Height measurements are estimated when recording an original using the photometric stereo principle, and an elevation scale factor must first be assigned to the resultant depth map in order for accurate measurements to be made from it. Comparing data from the Selene against data generated with a high-accuracy measuring device like the Lucida, or from an optical profilometer, has been essential in determining the correct scale factor.
In order to reveal details from originals with extremely shallow relief, it has been useful to increase the scale factor and in doing so, exaggerate differences in relative height. For instance, it has only been possible to produce usable shaded renders from many of the mezzotint printing plates captured for the project by increasing the scale factor.
Creating and sharing an archive of detailed shaded renders will no doubt be extremely useful for researchers, but given that the data recorded for ARCHiOx is truly three-dimensional, the exciting possibility of creating accurate 3D facsimiles from items within our collections is entirely feasible.
For over twenty years, the Bodleian have archived hundreds-of-thousands of digital images, captured from our collections. Through the use of technologies like the Selene and Lucida, we now have the capability of reproducing items more accurately than ever, not just as a two-dimensional representations, but as tangible 3D recreations.
This next-level development in preservation is not only important for the conservation of the original. Faithfully reproduced, three-dimensional reproductions will allow students to have a less restrictive, more hands-on experience of some of the more delicate and difficult to access items in our collections. 3D facsimiles may also be used as a substitute for originals while temporarily unavailable due to being exhibited or undergoing conservation treatment.
Recreating an accurate and functional printing plate using data captured with the new photometric system is a demanding test for the Selene, but even more so for the elevated printing technology used to create the 3D facsimile. While the Selene is able to record over 1000 pixels for every linear inch of original, Factum Arte’s state-of-the-art large-format 3D printer is limited to around half of this resolution. Though this resolution has proved to be entirely adequate for the elevated printing of reproductions of artworks, the incredibly fine and often geometrically complex engraved details of copper plates are much harder to reproduce.
Commissioned by antiquarian Richard Rawlinson, Rawl. Copperplates e.65 is a copy of an earlier printing plate and features a wonderful portrait of local Oxford antiquarian Anthony Wood, whose manuscript and book collections are held at the Bodleian. A print from the new plate, engraved in 1709 by Michael Burghers, appears in Rawlinson’s own copy of his work, ‘The Life of Mr. Anthony a Wood’.
So, not for the first time, though perhaps for the first time in 313 years, a new copy of the Anthony Wood plate would be remade, inked and pulled through a printing press. This time however, the copy would be made using the very latest digital technology, in Factum Arte’s print room in Madrid.
In order for the facsimile to be durable enough to be pulled through the printing press, it was initially necessary for the plate to be backed to a copper sheet. Having prepared and inserted a base, the 3D files were then uploaded to the elevated printer. The recently installed custom Canon Arizona printer deposits multiple layers of resin as the print head repeatedly travels over the base. These incredibly fine layers, measuring between just 2 and 4μm are hardened using ultra-violet light. Not only can the printer create texture, it can also reproduce the original’s colour. The process is time consuming, taking several minutes to build even the shallow relief of the printing plate.
With the elevated printing complete, the final challenge would be to print from the facsimile in order that comparisons could be made to the original prints from the Bodleian’s collections. Eager to produce the first prints, founder of the Factum Foundation, Adam Lowe used both a modern press and a replica Goya press to produce a preliminary batch of 2022 editions. The prints are impressive, reproducing the incredibly fine cross hatching surrounding the central portrait. This is an impressive achievement given that it is the first time that a printing plate has been produced using the new photometric stereo recording system. It is likely that differences between the quality of the original prints and the reproductions can mostly be attributed to the limitations of the 3D printing technology rather than the 3D data generated by the Selene, but future developments in both technologies will no doubt lead to increased accuracy.
Having now captured dozens of the Bodleian’s 18th-century copper printing plates for the ARCHiOx project, it has been a pleasure to show visitors to the Bodleian’s Imaging studio both the originals and the newly recorded digital renditions. The results from the Selene have generated a great deal of excitement from curators, conservators and researchers. Coming at the same time as the doctoral research of Chiara Betti, and following publications by Anna Marie Roos, Jeremy Coote, and Mark Crosby, this project extends the library’s efforts to make these previously neglected relics of printing and book history accessible to researchers.
This technology has enormous potential for the capture of cultural heritage material and has greatly exceeded the expectations of all involved in the project. But equal to the enthusiasm for the new technology and its output, visitors have universally expressed a greater appreciation of the skill and dedication of the engravers who made and printed from the original copper plates. These items deserve to be recorded as perfectly as technology will allow. In doing so these wonderful objects can be shared digitally for the research and enjoyment of everyone.
But recording a selection of the Bodleian’s copper printing plates is only the initial focus of ARCHiOx. Now that the technology has been proven and refined, other collections which will benefit from 2.5D capture can be recorded. From a Rembrandt portrait to a volume of Japanese Ukiyoe prints, and a mysterious collection of incised palm-leaf manuscripts, the Selene and Lucida will be used to reveal further exciting discoveries and record originals as never before.
Developments and output from the project will be recorded in a future post.
Text and images (unless otherwise credited) by John Barrett, April 2022
With thanks for their assistance in writing this article:
Jorge Cano, designer and engineer for Factum Arte and the Factum Foundation. Jorge is the designer of the Selene, has established the photometric stereo workflow used for ARCHiOx and has been responsible for my training with this exciting new technology.
Chiara Betti, researcher of the Rawlinson copper plate collection. The working title of Chiara’s thesis is ‘The Rawlinson copper plates at the Bodleian Libraries’. Readers with an interest in Chiara’s research are encouraged to contact her at email@example.com. The research is funded by the AHRC through the Collaborative Doctoral Partnership. See: https://www.glam.ox.ac.uk/early-modern-copper-plates-bodleian-libraries
The incredible work of the Factum Foundation is documented on their website www.factumfoundation.org
This exciting project has been made possible through the generous funding support of the Helen Hamlyn Trust.
6 thoughts on “ARCHiOx: research and development in imaging”
Comments are closed.