Digital Infra-Red Photography for Recording Painted Rock Art

Article excerpt

Here is a new application of infra-red photography with a digital camera to record rock art. The need to make full and accurate records of the images, without touching (and thus degrading) the rock, requires a method of remote mapping. Trials with digital IR reported here are very promising and especially useful for painted rock art.

Keywords: digital photography, field recording, infra-red, rock art, survey

Introduction

Since rock art cannot be taken back to the lab for study, archaeologists must find ways to record relevant information about it in formats applicable to both research and site preservation. During the current renaissance in rock art studies, the views of researchers and site conservators regarding acceptable recording practices have moved increasingly towards methods that minimise damage to the rock surface. Such methods as plaster or latex casting, tracing onto transparent drafting medium, chalking, moulding, and making rubbings are no longer considered either necessary or acceptable by most professional archaeologists and conservators (Loendorf 2001; Simpson et al. 2004; Chandler et al. 2005: 119-20; Trinks et al. 2005). With the rapid development of sophisticated digital imaging techniques, physical contact with the rock, or application of substances to it, is now considered not only bad for preservation bur also unnecessary for research. Software programs allow researchers to simulate different lighting conditions, to correct for parallax in drawings and photographs, to enhance images through manipulation of contrast and colour balance, and to digitally highlight particular elements so that others can more easily see what the researcher finds relevant (Rip 1983; Valiga & Goerz 1987; Aujoulat 1993; Ogleby 1995; Clogg et al. 2000; David et al. 2003; Brady et al. 2004; Chandler et al. 2005: 120).

An old technique with improved applicability to rock art research is infra-red photography or, in its modern incarnation, digital infra-red imaging. Along with ultraviolet and multispectral imaging, infra-red extends the range of visibility of some pigments (Clark 1954; Moss 1954; Pedersen 1953-4; Holliday 1961; Aujoulat 1993; Hartley et al. 1993: 18; Clogg et al. 2000; Loendorf 2001; Chabries et at. 2003; Solodeynikov 2005). It allows the camera to detect portions of the colour spectrum that are not visible to the human eye or by using conventional photography. Infra-red imaging has its limits, as will be discussed below; however, we feel that digital cameras now make it a possibility in field situations in which infra-red film photography is impractical. It requires no highly specialised or expensive equipment. Many field archaeologists will find that their 'good' digital camera is readily adaptable to the technique. Further, the technique described here requires no specialised knowledge or software that would hinder its routine use by non-specialists. In comparison to more complicated recording methods such as multi-spectral imaging, we think that the method for infra-red imaging described here makes up in accessibility what it sacrifices in comprehensiveness. It can easily be added to a basic rock art recording regimen (Wainwright 1990; Loendorf 2001). What one method misses, another may pick up; thus, adding a method to the suite used at any given site can quantitatively and qualitatively improve the research data base.

Infra-red photography in archaeology and conservation

Infra-red photography captures the red end of the colour spectrum beyond standard colour and black and white film. Both film and digital cameras are designed to minimise detection of infra-red and ultraviolet radiation, because these interfere with the sharpness of images made in visible light. Because of this sensitivity to light not recorded on standard films or digital settings, infra-red photography can yield clearer images of some heavily weathered pigments. Its effectiveness depends on the infra-red reflectivity of the particular pigment and materials that overlay it. …