Digital enhancement of Torres Strait rock-art.

MCNIVEN, IAN J. ; DAVID, BRUNO ; BRAYER, JOHN 等

Eight thousand years ago, the land bridge linking New Guinea and Australia into a single landmass finally sundered under post-glacial rising seas. Today, over 150 rocky, muddy and sandy islands form Torres Strait. The region is home to numerous inter-connected Islander communities who still maintain their specialist maritime fishing and hunting ways along with totemic associations with the sea. A key question for Torres Strait archaeology is to what extent settlement was dependent upon ceremonial, economic and socio-political alliances between islands and between islands and adjacent mainland areas (see McNiven 1998). Similarly, were long-term developments in linkages and boundaries across Torres Strait expressed stylistically in material culture?

Such questions are being addressed through a new archaeological project investigating rock-art styles and pigments (ochres) across Torres Strait, from southern Papua to the tip of northeastern mainland Australia (Cape York Peninsula). To date, 33 rock-art sites and seven ochre sources have been recorded on Torres Strait islands (McNiven et al. in press). Our project, the first systematic study of Torres Strait rock-art, is exploring spatial patterning of specific artistic conventions and pigments through time to determine the changing geography of cultural influences. Yet in such tropical, coastal settings many of the older rock paintings can be expected to have faded beyond visibility, and so recording methods need to employ techniques that maximize our chances of recovering this art. Here we report our first attempts at exploring such a possibility, using digital image enhancement techniques on the rock painting site of Kabadul Kula on Dauan Island.

Kabadul Kula is a large granite boulder with a shallow overhang under which 44 red paintings are evident. Islander history recalls that the paintings were made some time ago (possibly 19th century) by a group of Kiwai Island raiders (Kupamal) who had canoed 140 km down from the mouth of the Fly River to the northeast. After their secret landing, the raiders drew pictures with red ochre (parma) on the underside of the granite boulder now known as Kabadul Kula. The next morning, they attacked the village of Bull, killing many with their stone-headed clubs (gabagaba) and cutting off their victims' heads with bamboo knives (upi). The raiders managed their escape, but not before a number were killed by Dauan warriors (Lawrie 1970: 143-7).

Many of the paintings at Kabadul Kula remain clear today. In April 2000, we visited the site, recording each painting with conventional and digital photography (FIGURE 1). The initial enhancement, undertaken principally by increasing the contrast and saturation (purity) of colours with Adobe Photoshop, was always applied to an entire photograph. When previously unknown or faded paintings were revealed, they were re-photographed and further enhanced by manipulating images in Photoshop's HSB, RGB, CMYK and Lab enhancement modes (various means of describing and digitally manipulating colour balances) (see Adobe Photoshop 5.0 User Guide: 63-5).

[Figure 1 ILLUSTRATION OMITTED]

Digital enhancement revealed numerous previously unknown or unrecognizable images, some in styles different to those thought to have been undertaken by Kiwai raiders. One implication is that the rock was already decorated when the raiders decided to inscribe it with their own marks. The clarity of the enhanced images promises to enable systematic study not only of the most recent phase of rock-painting activity in Torres Strait, but older, more faded paintings as well. A significant advantage of recording digitally has been our ability immediately to communicate results back to local community members (particularly those physically unable to visit sites) and in the process to discuss the cultural and scientific significance of sites. Digital photography also allows further exploration of parts of a site that require focused attention without having to return to the site in multiple recording stages. The enhanced images from Kabadul Kula revealed important cultural information, such as an anthropomorph with a fish headdress of a type used historically in Torres Strait (Haddon 1912); previously unknown large-toothed anthropomorph with a possible shield (a material culture item unknown historically in Torres Strait) (FIGURE 2); and an insect-like depiction (FIGURE 3). This project has confirmed the ability of obtaining relatively ancient, faded rock-art data through digital photography and computer enhancement.

[Figures 2-3 ILLUSTRATION OMITTED]

Acknowledgements. This project was kindly funded by a grant from the Australian Institute of Aboriginal and Torres Strait Islander Studies, Canberra. Logistical support was provided by Garrick Hitchcock and Kevin Murphy. Special thanks to the Dauan Island community, especially Margaret Mau (Chairperson), Abraham Mau and Phillip Biggie, for hospitality, support and advice.

References

HADDON, A.C. (ed.) 1912. Reports of the Cambridge Anthropological Expedition to Torres Straits IV. Cambridge: Cambridge University Press.

LAWRIE, M. 1970. Myths and legends of Torres Strait. St Lucia: University of Queensland Press.

MCNIVEN, I.J. 1998. Enmity and amity: Reconsidering stoneheaded club (gabagaba) procurement and trade in Torres Strait, Oceania 69(2): 94-115.

MCNIVEN, I.J., J. CORDELL & J. FITZPATRICK. In press. An Islander world: new approaches to managing the archaeological heritage of Torres Strait, northeast Australia, Memoirs of the Queensland Museum, Cultural Heritage Series.

IAN J. MCNIVEN, BRUNO DAVID & JOHN BRAYER, McNiven, School of Fine Arts, Classical Studies & Archaeology, The University of Melbourne, Parkville, Victoria 3010, Australia. i.mcniven@finearts.unimelb.edu.au David, Department of Geography & Environmental Science, Monash University, Clayton, Victoria 3800, Australia. Bruno.David@arts.monash.edu.au Brayer, Department of Computer Science, University of New Mexico, Albuquerque NM 87131-1386, USA. Brayer@cs.unm.edu