Documenting and Analyzing Rock, Paintings from Torres Strait, NE Australia, with Digital Photography and Computer Image Enhancement

Abstract

The deterioration of rock-art over time is an important concernfOr indigenous communities) archaeologists) rock-art researchers)and cultural heritage managers.Computer enhancement has emewed as an important tool in viewing poorly visible rockpaintings. While most studies regarding this technique explore the methods associated with computer enhancement here is little discussion of the results that can begenerated beyond the recovery of images. This article presents results from the application of computer enhancement methods to rock paintings from the Torres Strait region in NE Queensland. The results obtained through the computer enhancement of deteriorated rock paintings are used to reveal degrees of preservation) interregional interaction) and previously undocumented spatial patterning across the strait. IntroductionThe creation of art on rock is a fIXed,tangible expression of an artist's visual culture. Yetthe permanency of these artworks over time is variable. Many artworks are damaged by both anthropogenic (e.g., graffiti) and natural factors (e.g., water or fire damage), which decrease the visibility of images over time. Documentation of rock-art (paintings, stencils, and engravings) by professional rock-art recorders, archaeologists, and indigenous communities has until recently been undertaken by recording and analyzing those images that can still be viewed with the nal(ed eye. Strategies for recording these images include making simple sketches, drawings, tracings, rubbings, and using conventional film photography. But how can we study those images that have deteriorated or faded to such a point that they can no longer be viewed or recorded using conventional techniques? Furthermore, how can those images that have experienced considerable deterioration over time contribute to the analysis and interpretation of a region's rock-art assemblage? The introduction of digital technology and computer enhancement methods into rock-art recording presents researchers with an opportunity to record and examine heavily deteriorated images that would have been missed using conventional recording techruques.In this paper, I review the development of digital tech-

Digital image enhancement with DStretch®: Is complexity always necessary for efficiency?

“…The importance of subjectivity in the recording of pictograms or petroglyphs is now aknowledged (Lorblanchet, 1984: 43-44;Ucko, 1992;Bednarik, 1992;Le Quellec, 1994;Brady, 2006;Le Quellec, 2007;Seoane Veiga, 2009: 40;Le Quellec et al, 2009;Dobrez, 2011). Digital enhancement is generally viewed as a way to reduce subjectivity, but even if "tool's eye forces human's one to be more rigorous" (Paillet, 1998: 17), one cannot believe that computer processing would totally eliminate the subjective nature of our readings.…”

“…: Montero Ruiz et al, 1998;Kamal et al, 1999;Clogg and Díaz-Andreu, 2000;Brady, 2007;David et al, 2007;López-Montalvo and Domingo-Sanz, 2009;Gutiérrez Calvache and González Tendero, 2010;Rogerio-Candelara, 2010;Ortiz-Sanz et al, 2010;López-Montalvo, 2010;RogerioCandelara et al, 2011;Hollmann and Crause, 2011;Förster, 2013;Ruiz and Pereira, 2014). Compared to previous methodologies (hand sketch, direct tracing or tracing from film photography), the new tools constituting what Brady and Gunn call "the digital revolution" (Brady et al, 2012: 628) provide numerous advantages, like more comprehensive inventories of paintings (McNiven et al, 2004;Brady, 2006), more precise and objective tracings, and help for superimpositions studies (Gunn et al, 2010), while avoiding direct contact with pigments.…”

“…Among those currently available, the "standard" one since more than ten years is Adobe Photoshop © , a very powerful tool (Mark and Billo, 2002;Domingo Sanz and López-Montalvo, 2002;McNiven et al, 2004;Brady, 2006Brady, , 2007. Good alternatives are ImageJ s (written in java, open source, with a worldwide users community), and Hypercube s (a Spectral Imagery Analysis Software freely distributed by the US Army Topographic Engineering Center).…”

Rock art as microtopography

“…While there is still a discourse on the objectivity of image enhancement (Read & Chippindale, ), it is widely accepted by rock art researchers as reducing subjectivity (Brady, ; Brady & Gunn, ; David, Brayer, McNiven, & Watchman, ; Le Quellec, Duquesnoy, & Defrasne, ). Image processing with DStretch ® (Burton, Adams, Willis, & Nadel, ; Defrasne, ; Gunn et al., ; Harman, ; Le Quellec et al., ; Taçon et al., , , ; Tan, Sokrithy, Than, & Chan, ), Adobe ® Photoshop ® software (Brady, ; David et al., ; Domingo, Villaverde, López‐Montalvo, Lerma, & Cabrelles, ; Gunn et al., ; Mark & Billo, ), and other photograph manipulation software (Clogg, Dı́az‐Andreu, & Larkman, ) are currently an integral part of recording and digital tracing of painted rock art sites.…”

“…Photograph manipulation software is used to change contrast, hue, saturation, curves, levels, and other parameters to distinguish the art from the rock (Brady, ; Mark & Billo, ). When DStretch ® was developed by Harman () with preset calibrations known as color spaces (such as LAB, YDS, YBR, etc.)…”