Digital Enhancement of Torres Strait Rock-Art

Article excerpt

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. …