3D capture, representation and manipulation of cuneiform tablets Sandra I. Woolley *, Nicholas J. Flowers , Theodoros N. Arvanitis , Alasdair Livingstone , Tom R. Davis and John Ellison
The University of Birmingham, Edgbaston, Birmingham, England Harvard University, Cambridge, MA 02138, USA ABSTRACT
This paper presents the digital imaging results of a collaborative research project working toward the generation of an online interactive digital image database of signs from ancient cuneiform tablets. An important aim of this project is the application of forensic analysis to the cuneiform symbols to identify scribal hands. Cuneiform tablets are amongst the earliest records of written communication, and could be considered as one of the original information technologies; an accessible, portable and robust medium for communication across distance and time. The earliest examples are up to 5,000 years old, and the writing technique remained in use for some 3,000 years. Unfortunately, only a small fraction of these tablets can be made available for display in museums and much important academic work has yet to be performed on the very large numbers of tablets to which there is necessarily restricted access. Our paper will describe the challenges encountered in the 2D image capture of a sample set of tablets held in the British Museum, explaining the motivation for attempting 3D imaging and the results of initial experiments scanning the smaller, more densely inscribed cuneiform tablets. We will also discuss the tractability of 3D digital capture, representation and manipulation, and investigate the requirements for scaleable data compression and transmission methods. Additional information can be found on the project website: www.cuneiform.net Keywords: 3D imaging, cuneiform tablets, laser scanning, forensic analysis, data archival, data compression.
1. CUNEIFORM TABLETS Cuneiform tablets1 are rectangular slabs of sun-dried or fired clay, moulded by hand and inscribed when wet with a wedgeshaped stylus. Cuneiform (from the Latin word cuneus, meaning wedge) was the most common system of writing in Western Asia from 3000 BC through to the middle of the first millennium BC when it was gradually replaced with various alphabetic systems of writing. The signs are typically 3 mm in height, with about 30 signs per line and 25 lines of writing both on the front and back of the tablet. The Scottish engineer James Nasmyth first came to live in London in 1829 and discovered the British Museum and their rapidly growing collection of cuneiform tablets, on which the work of decipherment was progressing apace. He later wrote in his biography 2, "I was specially impressed and interested with the so-called "Arrow-head" or "Cuneiform Inscriptions" in the Assyrian Department. ... I was particularly impressed with the precision and simple beauty of these cuneiform inscriptions". This interest motivated him to investigate the mechanics of cuneiform production including the reed stylus and the roller seal, now commonly referred to as a cylinder seal, as shown in Figure 1. The dimensions of a cuneiform tablet can range from those of a credit card to those of a palmtop computer, the so-called "monster tablets", and were inscribed by means of a square-profiled reed stylus that made triangular indentations, or wedges, with “tails”. *
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Three-Dimensional Image Capture and Applications IV, Brian D. Corner, Joseph H. Nurre, Roy P. Pargas, Editors, Proceedings of SPIE Vol. 4298 (2001) © 2001 SPIE. · 0277-786X/01/$15.00
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Figure 1: James Nasmyth the 19th century engineer and his early descriptions of cuneiform production 2
An example of a neo-Babylonian tablet and script details are shown in Figure 2. As can be seen, each sign consists of a number of wedges. Along with ancient Egyptian and Chinese writings, these tablets are among the earliest records of written communication. Cuneiform writing itself developed a number of different varieties, and the tablets were also later inscribed with early forms of the alphabet that we still use today. The earliest examples are up to 5,000 years old, and the writing technique remained in use for some 3,000 years. The writing was deciphered in the last 150 years; hundreds of thousands of tablets have been discovered and are now preserved in museum archives. Unfortunately, only a small fraction of these tablets can be made available for display and much important academic work has yet to be performed on the very large numbers of tablets to which there is necessarily restricted access.
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Figure 2: Examples of cuneiform tablets a) neo-Babylonian b) detail of Neo-Babylonian script from tablet (a) and c) neo-Assyrian detail
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2. THE CUNEIFORM DIGITAL FORENSIC PROJECT (CDFP) 2.1. Background The CDFP3 began in January 1999. It is a multidisciplinary project funded by The University of Birmingham, U.K. Our team includes an Assyriologist, a forensic handwriting expert and engineers specialising in database design and digital imaging; all are members of the University of Birmingham, UK. The main objective of the CDFP is the development of a digital cuneiform sign database4 requiring digitization of cuneiform tablets and signs, and the scientific forensic analysis of cuneiform sign configurations. Much of the cuneiform material is fragmentary; excavations performed in the 19th century lacked the rigor of modern scientific archaeology, with the result that much material is unprovenanced. Traditional cuneiform sign lists, both ancient and modern, have always recognised the existence of a variety of script forms pertaining to different areas and periods in the long history of the diverse civilisations that used the cuneiform script. In addition, scholars who have specialised in particular cultural complexes - rural, urban, temple, palace - with large numbers of tablets belonging to one area and period have frequently maintained that they can recognise the handwriting of individual scribes. The digitization of the cuneiform texts is an important first step in the development of a forensic database for scholarly research. It is hoped that our research activities will assist in enabling tablets to be assigned scientifically to the archives or contexts to which they belong, with implications for the documentary history of the areas concerned, thus providing objective support for expert knowledge. The digital imaging aspects of the work involve 2D and 3D imaging, and the delivery of a CD and www-accessible digital library for both research and teaching activities.
3. DATASETS FROM THE 1ST MILLENNIUM BC Two culturally specific areas have been targeted for concentrated work by the CDFP, an area where kings and courtesans rub shoulders with an elite of scholars on one hand, and a rather plebian ancient college of further education on the other. Each of these areas provides an extremely complex set of data. The first of these brings the project to the project to the palaces and royal halls of the mighty Assyrian Empire in the 7th century BC. It is known that a group of twenty or so learned men, the "inner circle", served as advisers to the kings Esarhaddon (680-669 BC) and Ashurbanipal (668-627 BC), while other groups of scribes and scholars at the court are also represented by copious cuneiform documentation in the form of letters and reports. The project has been using digital and forensic analysis to study the structure of the system of advisory personnel of the royal court. This investigation recently led to the discovery that a tablet found at Nineveh may in fact have been written personally by or for Ashurbanipal, probably while he was crown prince. It is well known that Ashurbanipal claimed literacy in a royal inscription and that as king he founded at Nineveh a massive library, some twenty-three thousand tablets and fragments of which are now in the British Museum. In addition, several crudely written tablets seem to be the work of Ashurbanipal himself, since the script shows similarities to the script of tablets signed by the scribe Balasi, who was appointed as Ashurbanipal's teacher. A letter to Ashurbanipal from his young brother (laku) survives. Perhaps most fascinating is a letter to Ashurbanipal's young wife Libbi-ali-sharrat ("O-city-she-is-queen!") from his elder sister Sherua-etirat ("Goddess-Sherua-is-the-one-who-saves!) concerning writing a tablet and reading it out. Sherua-etirat reminds Libbi-ali-sharrat that she is a "daughter of Akkad" and now a member of the ruling family in the "house of succession". By establishing a database of sign forms and individual cuneiform script types (hands) the project is contributing to the investigation of the cult literacy and the indigenous interest in cuneiform surrounding Ashurbanipal as crown prince of Assyria. The second area involves an archive of tablets which has recently been literally pieced together by I.L.Finkel of the Dept of Western Asiatic Antiquities of the British Museum. These tablets date to the reigns of the Persian kings of Babylon Darius and Xerxes, about two hundred years later than the material referred to above. Certain peculiarities of the documents such as spelling mistakes and multiple copies of the same documents in different hands show that what is involved here is a scribal school. The schoolmaster himself can be identified and it seems that he used various kinds of written material at his disposal in his instruction. The level is higher than that of a primary school and could be compared to a college. There are two varieties of instructional material, namely documents of a business nature such as contracts, and medical texts. This
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was then a Babylonian college of business and medicine. It provides an ideal dataset for the project aims of forensic handwriting analysis and database construction.
4. PHOTOGRAPHY The digital imaging of cuneiform tablets poses a number of challenges. Central to the challenges is the fact that many of the tablets contain densely compacted inscriptions on both sides, with text running over rounded edges and frequently continuing along each side edge, making the complete 2D capture of symbol sets problematic even with many exposures from different angles. Our initial experiments involved SLR photography at the British Museum, using a four-light bed with adjustable camera height and with tablets mounted on a sand tray to stabilise their orientation (Figure 3). Lighting proved problematic, not least because of repeated burns from the directional spotlights. The depth of the impressions also made the selection of correct lighting both difficult and time-consuming. North-west lighting is usually preferred for illumination of cuneiform script and did produce the best results. Soft, neon, north-west lighting was later adopted; however, many images, and occasionally whole reels of film were discarded on subsequent examination. Analogue photographic capture was ruled out as a tractable method for capture of the cuneiform datasets primarily because of the difficulty of preserving scale and context information, the inability to annotate (i.e. properly label) images, the continuous and complex adjustments to accommodate the tablet surfaces, and, importantly, the absence of direct visual feedback.
4.1. Image resolution and format In addition to cuneiform experts, others may also wish to view cuneiform tablets. For example, the optical recognition of characters presents a number of interesting challenges to researchers5, 6. Some viewers may only interested in the general shape and size of the tablets, and a simple, low-resolution model may suffice. Other scholars may be interested in reading the symbols and would therefore require more intelligible, higher resolution renditions. However, the highest level of detail is required by forensic analysts. Discussions with forensic experts indicate that a resolution of approximately 0.025mm is required to distinguish between different scribal hands. Our interest in both sign recognition and forensic analysis dictated high-resolution capture, which proved particularly difficult in the case of the smaller tablets. Conventional NTSC video cameras are convenient to use but only provide 480 lines of resolution, although many video capture devices offer higher resolution. This increased resolution is obtained by interpolation and smoothing, and although these techniques improve the visual quality of the image, the additional resolution is artificial and cannot be used for forensic analysis. The lossless 256-color GIF image format was selected as the most efficient format for 2D images because the highresolution color information of the baseline JPEG standard was not required. GIF was also preferred because of its universal support, in particular, its support in www browsers. New still digital cameras now provide significantly higher resolutions but have practical limitations, in particular, storage capacity and battery life. We used two digital image capture techniques; a simple video camera capture system and a 3.34 megapixel digital camera (The Nikon CoolPix 990), using both zip and CD disc media. The video camera capture resolution proved insufficient for forensic purposes. The digital camera produced images of much more acceptable resolutions, but both techniques required continuous lighting adjustments and frustrating power supply, laptop computer, software and media logistics. Other logistical problems included the regular transport of various pieces of equipment to the museum (much improved by the museum's kind co-operation in storing the light bed and camera), the precious nature of the objects which required
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extreme care in handling at all times, the lack of on-site high-bandwidth networking, and, the need to continuously annotate captured details (requiring our expert Assyriologist). When reading the tablets, experts tend to rotate them constantly; grossly in order to present all the signs to inspection, but also subtly, in order to use light and shadow to bring out the indentations clearly. In a digitised tablet, this manipulation would ideally be enabled by high-resolution 3D rendering, rotation control and light source adjustment.
Figure 3 : Image capture in the British Museum cuneiform archives
5. 3D SCANNING There are a number of different techniques for capturing 3D models, each offering different scanning areas and resolutions. The Digital Michelangelo project at Stanford University7 involved scanning larger objects, e.g., Michael Angelo's statue of David, at a resolution of up to 0.25mm using laser triangulation rangefinding. The 3D -Matic project8 at the Turing Institute and The University of Glasgow used ‘photogrammetry’ to give a resolution of 0.5mm. Commercial laser stripe triangulation systems9 can deliver resolutions of 0.1mm (potentially 0.05mm). Surface contact probes can achieve similar resolutions, but they make physical contact with the object obviating their application to precious or fragile objects and the scans are very slow; for example, it would take approximately three days to scan one face of a 50mm by 70mm cuneiform tablet. The best technique may be moiré, which theoretically offers very high resolution10 although commercially available portable moiré scanners offer resolutions of closer to 0.2mm. Table 1 summarizes the differences between the various scanning techniques.
Technique Photogrammetry Laser Stripe Triangulation Contact Probe Morié (commercial) Morié (theoretical)
Scan size (mm) 2000 2000
Resolution (mm) 0.5 0.05
Scan time for one side (s)
