Three-dimensional imaging in archaeology: its history and future.

NICHOLSON, PAUL T.

Introduction

Photography is currently undergoing a revolution. Digital cameras have already begun to replace conventional film images, and are increasingly finding use on archaeological sites. The wide use of computing has also led to the combining of images with graphics software to produce `virtual reality' images of buildings and landscapes. Such techniques will surely establish themselves in archaeology, but for the moment they do have limitations, and there are useful alternatives.

One of these alternatives is stereoscopic photography, also known as stereography or 3D photography. This technique has enjoyed sporadic use in archaeology in the past, but as conventional photography has developed it has tended to be overlooked. The rise and -- more especially -- the fall of 3D moving pictures fostered the belief that stereo photography was little more than a gimmick. The purpose of this paper is to review the use of this technique in archaeology and to suggest ways in which it can be further developed as archaeological photography enters the 21st century.

Principles

Stereo photography may fairly be described as `Victorian virtual reality'. The technique was `conceived in the infant years of photography and was perfected between 1850 and 1854' (Darrah 1977: 1). The concept built on the still earlier development of stereoscopic drawing which, like stereo photography, has now become a rarity.

The principle is a simple one and, given that we see in three dimensions, one which might have been expected to hold an important position in both modern photography and archaeology. The technique relies on two photographs taken with an appropriate distance between them, such that when they are viewed with a stereoscope the effect produced appears to be three-dimensional. The distance between the camera-lens positions can be as little as 65 mm, approximately the distance between the human eyes, and many regard this distance as the optimum for `true' stereo photography. In practice however, greater distances are often used to produce what is more correctly known as `hyper stereo'. This has the effect of enhancing the three-dimensional effect seen by the viewer.

Images may be produced in a number of ways. A single camera can be used to produce two images at a distance apart, the method used in the earliest stereo photographs. This is only suitable for stationary subjects, but is a technique that can readily be used for recording sites etc. today. Secondly, a purpose-built stereoscopic camera may be used, which records a pair of images each time it is operated. Such cameras are today both relatively rare and often expensive, since few manufacturers produce them, and the market in second-hand equipment is limited. Third, a pair of cameras may be mounted together on a bar and synchronized, providing a cheap and versatile system (for currently available options see Stereoscopic Society 1999: 23-5). `Beam splitter' devices are also available for standard SLR cameras, but the format of the images and overall quality are often regarded as unsatisfactory.

Although, with practice, it is possible to view stereoscopic images with the naked eye (a technique known as `free viewing'), it is usual to view them through some kind of viewing device. The simplest of these is the stereoscope. This comprises a pair of lenses mounted in a frame, often with some kind of divider between the lenses to ensure that the viewer sees only the left image with the left eye, and the right with the right. Many archaeologists will be familiar with such devices from work with aerial photographs.

It should be stressed that, although the earliest stereographs were black-and-white prints, it is possible to view colour transparencies in the same way. However, colour transparencies can also be projected in stereo, and this may be of particular value in archaeology where enlarged images are required. Projection is most commonly achieved using two projectors, set either one above the other or side by side. One projector is used for the left image of the pair, the other for the right. In front of each projector is placed a polarizing filter, set at 90 [degrees] to one another. The pair of projectors is aligned using a pair of set-up transparencies designed for the purpose and the images projected onto a silvered screen (rather than a white one) which is necessary for polarization. The images are viewed through polarizing spectacles, also with appropriately oriented lenses, so that each eye can see only one image. The result appears as a three-dimensional image.

Stereographs in archaeology

Most of us have, at some time, used stereoscopic pairs of aerial photographs as a convenient means of viewing the landscape for the detection or mapping of sites which would be difficult to spot using a single mono image. The technique was developed from the military use of such aerial photographs, a use which was recorded for posterity by Glyn Daniel by his appearance in the propaganda film made by the Central Office For Information, Target for Tonight!

Dorrell (1994) in his Photography in archaeology and conservation discusses stereo photography only in so far as aerial photography and photography from a tower or frame is concerned. It is not featured at all in the introductory section dealing with the history of archaeological photography. Despite this, stereo photography has played a useful, if so far peripheral, role in archaeological recording.

This recording goes back to the earliest period of photographic history. Because stereography was developing alongside what is now considered `conventional' photography it would not have seemed at all `odd' to Victorian viewers or practitioners, any more than digital photography might be regarded as an oddity in our own time. This is forcibly demonstrated by the enormous market which developed for stereographs. The American publishing company of Underwood & Underwood was producing 25,000 stereographs per day by 1901, covering between 30,000 and 40,000 titles, while the Keystone View Company had produced over 40,000 titles by the time its main production ceased in 1940 (Darrah 1977: 47-9). Stereoscopes were similarly common with Underwood & Underwood producing 300,000 a year by 1901, so that it could be said that `... there is no parlor in America where there is not a stereoscope' (Vogel, quoted in Veasey 1978: 5). The demand for stereo images was certainly not confined to America, and US as well as European companies spread them widely across the world.

Furthermore, `stereoscopic cameras were cheaper, lighter and less cumbersome ... offering freedom of use without complications or constraints. Travellers could envisage taking such a camera on remote expeditions' (Richard 1998: 177). In this respect the development of cameras suitably compact for field use owes much to stereography. It is not surprising, then, to discover that they found a documentary role in often remote parts of the world.

Why was the medium popular and what relevance does it have to archaeology? Its popularity should be self-evident. In an era before television it offered the general public, many of whom could not afford foreign travel, views of distant places, peoples and events, and did this in three dimensions (cf. Wing 1996: 147, figure). It was the closest to `being there' that most people would ever experience. We see in three dimensions and stereographs simply exploited that obvious fact. Certain publishers deliberately built on the idea of `being there'. Underwood & Underwood developed their patent `travel system', consisting of sets of stereoscopic images accompanied by a hardback book written by an expert on the area or topic concerned and accompanied by detailed maps which showed the vantage point from which the photograph was taken and the area encompassed by the view.

This system was used by Underwood & Underwood in preparing their set of 100 photographs of Egypt, published in 1900, the travel book and maps being issued in 1905. The book was the work of James Henry Breasted (Breasted 1905), Professor of Egyptology at the Oriental Institute, Chicago, and gave a full description of each view, with careful mention of its location number on the map, as well as relating it to near-by views. This series is one of the two finest of Egypt ever produced (FIGURES 1-3), covering both ancient monuments and `ethnographic' or contemporary scenes. This series, with its accompanying book, provides a valuable record of Egypt in the period 1895-1904. With it, it is possible to identify the changes which have taken place in Cairo and elsewhere, as well as to view the changes to monuments themselves following excavation and reconstruction.

[ILLUSTRATIONS OMITTED]

Significant perhaps, are some of the views of Karnak (Egypt, nos. 54 and 55) which show the avenue of cryosphinxes being excavated complete with Decauville Railway -- and the avenue after excavation (the first copyrighted in 1896, the second in 1904) (FIGURES 1 & 2). The elaborate bracing used at the entrance to the hypostyle hall and the ruinous condition of the (now restored) Second Pylon at the site are also clearly visible. A view of Deir el-Bahri, which featured in the original Egypt series (Underwood & Underwood Egypt, copyright 1896, position 32) but was later replaced, shows the site soon after De Morgan's excavations, but prior to its extensive reconstruction. Other archaeological `excavations' are somewhat less well served, although views of them do exist. Underwood & Underwood include a view which purports to show `Excavations on the mound of Ur of the Chaldees', but which is clearly a staged image at the site, showing some of the local people who may or may not have been employed in excavation.

Stereographs also record various aspects of the life of indigenous peoples, some of whom were already starting to disappear as early as the time of the first stereographers. For example, no. 5 in the Egypt set shows a kind of sedan carriage, carried between two camels and used to convey a bride to her wedding (FIGURE 3). Breasted (1905) notes that this conveyance was already outmoded, and disappearing. This image was made in 1895 and, unlike most others, not updated in 1904, suggesting that by that time it was not easily possible to re-photograph what was already a `staged' scene.

At a time when ethnoarchaeology is well established, and there is an increasing interest in how traditional crafts were practised, these antique stereographs can be especially valuable. For example, amongst a series of views of the Near East we find the building of `the peculiar round boats called "Kufaa" on the Tigris River at Bagdad', an activity which presumably has not taken place there for some considerable time. The quality of images such as this is so high that details of the weave are visible. Numerous other ethnographic photographs of archaeological interest also exist, including the planting, harvesting and cooking of various crops, for example the making of bread among the Bedouin of Syria. Needless to say, as with many early `ethnographic' images a certain amount of caution is necessary, as photographers frequently `staged' images. However, in many scenes there is only limited scope for embellishment, and we are often presented with a genuine image. This is likely to be the case with images produced by the War Office during their survey of Sinai in 1868-9, a set which also included geological features. Indeed, the military were quick to see the potential of the method to render a `perfectly exact description of the relief of the battlefield' (Cosmos, March 1854, quoted in Richard 1998: 180). Such overt documentary and scientific uses of stereography were not at all uncommon, and the stereo camera accompanied several scientific expeditions of the late 19th and early 20th centuries.

Not only have cultural practices changed or disappeared during the last century, but whole landscapes have been altered and their archaeology destroyed. With this in mind it is well that we have the stereo images of Egypt produced by Frances Frith (published by Negretti & Zambra 1857-9) which include views of some of the monuments of Nubia, notable amongst them the temple at Gerf Husein, submerged as a result of the construction of the first Aswan Dam (see Weigall 1907: 81-3; parts of the temple are now at New Kalabshe and in the Nubia Museum, Aswan). Inscriptions and reliefs show particularly well in stereo, making them potentially valuable as guides to damage and deterioration which have taken place subsequently. Whilst Frith's is the best known, and best received, set of stereo views of Egypt it cannot be claimed that without it our knowledge of certain monuments would be greatly diminished. However, the fact that the views are in three, rather than two, dimensions does give us our only opportunity to view certain monuments as they actually appeared, something which a conventional photograph cannot provide for. We have the added advantage that the largest commercial manufacturers of stereographs tended to stamp them with copyright dates, or with a negative number which can be related to publication date. As a result we often have more closely dated stereo images than conventional images, further increasing their value as research tools.

The value of these images in industrial archaeology and social history cannot be underestimated. During the 19th century many new technological developments were photographed with this new recording medium, emphasizing the cutting-edge technology which they represented. Such images now form a valuable record for the industrial archaeologist. Scenes showing the construction of bridges are common, as are those of various steam vehicles and indeed of transport accidents. Certain industrial processes, such as the Japanese silk industry, were also documented by the stereo camera. Social historians will find interest in many of the domestic scenes portrayed, many of them in comic series. There are also views of domestic and public architecture which has now vanished. Military historians find interest in the extensive collections dealing with conflicts. The American Civil War, Boer War, Russo-Japanese war and First World War were all recorded by stereographers, although many of the action scenes were staged for the camera.

This is by no means the complete range of topics covered by this often overlooked archive source. However, stereoscopic photography has never died out, and is more practical today than at any time since its conception. With a growing interest in virtual reality it is worth considering how stereo photography might be used in the archaeology of today.

The future

Aerial photography and plan-photography from a frame have already been mentioned, and need not be considered further here. More recently the value of stereoscopic images has been realised in Scanning Electron Microscopy, where paired images have been used by microscopists to give 3D images of specimens. This technique has so far not been widely used in archaeology, perhaps because it has not been widely known, having been developed in the biological sciences, and is not featured in Olsen's (1988) review of SEM work in archaeology.

Stereography is also well suited to finds photography. Details such as weaving on cloth or basketry, relief on coins or metalwork and even cutting on glass can be photographed in such a way that they show more clearly than on a conventional image. This can be particularly useful for technological studies where such detail is important. Close-up photography can either be achieved using a stereo camera fitted with appropriate lenses or, more usually, with a single camera mounted on a sliding bar. After exposing the first image, the camera is moved one-thirtieth of the distance between the object and the lens and a second one made. The simple inter-ocular distance is not suitable for close-up work. Since the object is not moving there is no need for exposures to be made simultaneously so long as the same exposure is maintained.

Many excavations do not yet use digital photography, particularly in association with computer graphic imaging, because of constraints of either time, expense or expertise. Many archaeologists are more competent with a conventional camera than with computer software, and could benefit from stereo recording during excavation or survey.

I have used stereo photography, as an experiment, in three archaeological projects, and found it to be very useful. One of these projects was the survey and exploration of a catacomb of mummified ibis at north Saqqara, Egypt, undertaken on behalf of the Egypt Exploration Society. In the final season of work at the site I was loaned a simple stereo camera and used it to record some general views of the catacomb and particularly to illustrate stratigraphic relationships between areas of brickwork. Since the catacomb is too large and too confined to be lit by temporary electric lighting all work had to be conducted using caving lamps. As a result the flash photographs and video taken often show stratigraphic relationships and architectural details more clearly than they could be seen with the naked eye. The stereoscopic views show these features particularly well (FIGURE 4). It need hardly be emphasized that the technique would be well suited to the survey of standing buildings, either by photogrammetry or simply for the general recording of details. Equipment for drawing from such images is already available (G. Owen pers. comm.).

[ILLUSTRATION OMITTED]

I have also used the technique for a small amount of recording on a conventional excavation at Tell el-Amarna (Egypt) where it proved especially well suited to the recording of hollow features, such as kilns (FIGURES 5, 6), and will certainly use it as a standard technique in the future. The ability of the 3D technique to bring out minor variations in texture should make it valuable in the recording of stratigraphic sections. It should be stressed that although each stereo image requires two (usually simultaneous) exposures and therefore uses twice as much film, it is not actually as expensive as might be thought. Since it is possible to make such 3D images using a full-frame 35-mm camera (or twinned pair of cameras) either image in the pair can be used as a conventional 35-mm slide for mono-projection, printing as a publication image and so forth. It is not necessary to record a pair of stereo images and make a conventional mono image.

[ILLUSTRATIONS OMITTED]

The use of stereo images in ethnoarchaeological fieldwork should be apparent from what has already been said of its use during the 19th and 20th centuries. At a time when traditional societies are under ever greater threat it is particularly important that they be recorded in as much detail as possible.

Digital photography has already been mentioned, and it should be noted that it too can be used to produce stereo images. Already digital cameras have been rigged to produce paired images which can then be adjusted by computer to give stereoscopic output (see Stereoscopic Society 1999:24-5 on the Burder 3-D Digi-Cam). The combining of several such images taken at known distances and from known points can be used to produce more realistic virtual images than have thus commonly been produced.

In conclusion, I hope it has been demonstrated that archaeology can benefit from the intelligent use of stereoscopic photography, both as a research tool in the archive and as an instrument for contemporary recording. As a discipline we frequently pride ourselves on our 3D site recording, why then should we confine ourselves to 2D photographic recording?

Acknowledgements. I am grateful to Mr. Bob Aldridge of the Stereoscopic Society for his suggestion that I experiment with stereo photography during my fieldwork on behalf of the Egypt Exploration Society, and for his loan of a stereoscopic camera. Mr Martin Willsher kindly built the 35-mm twinned system which I currently use, whilst Mr Bernard Brown FRPS has provided much valuable advice on the mounting and projection of stereoscopic images.

Note. The images reproduced here can be viewed with the standard viewer used for stereoscopic aerial photographs or with a simple lorgnette viewer. Lorgnette viewers are available from Bernard Makinson, Stereoscopic Society, 36 Silverthorn Drive, Longdean Park, Hemel Hempstead HP3 8BX, UK at a cost of 2 [pounds sterling]. Please state that the lorgnette type viewer is required. Cheques should be made payable to the Stereoscopic Society.

References

BREASTED, J.H. 1905. Egypt through the stereoscope. New York (NY): Underwood & Underwood.

DARRAH, W.C. 1977 (1997). The world of stereographs. Reprint. Nashville (TN): Land Yacht Press.

DORRELL, P.G. 1994. Photography in archaeology and conservation. 2nd edition. Cambridge: Cambridge University Press.

OLSEN, S.L. 1988. Scanning Electron Microscopy in archaeology. Oxford: British Archaeological Reports. International series S452.

RICHARD, P.-M. 1998. Life in three dimensions, in M. Frizot (ed.), A new history of photography: 175-83. Cologne: Konemann.

STEREOSCOPIC SOCIETY. 1999. The journal guide to stereoscopic cameras, Journal of 3D Imaging 146 (October): 23-5.

VEASEY, B.A. (ed.). 1978. Egypt: a journey through the land of the Pharaohs. New York (NY): Camera/Graphic Press.

WEIGALL, A.E.P. 1907. A report on the antiquities of Lower Nubia. Oxford: Oxford University Press.

WING, P. 1996. Stereoscopes: the first one hundred years. Nashua (NH): Transition Publishing.

Received 29 August 2000, accepted 7 November, revised 10 January 2001

PAUL T. NICHOLSON, School of History & Archaeology, Cardiff University, PO Box 909, Cardiff CF10 3XU, Wales.