UNESCO Prehistoric Rock-Art Sites in the Côa Valley, a World Heritage Site in Portugal
Partners in Preservation
This project was completed in 2006. The following article about it is by Claudia Willen.
Cultural Heritage Imaging (CHI) co-founders Mark Mudge and Carla Schroer, and CHI's imaging director Marlin Lum, worked on site at UNESCO Prehistoric Rock-Art site in the remote Côa Valley in Portugal, where they applied CHI digital imaging tools and technologies to create 3D reflection transformation images (RTIs) of two types of prehistoric rock art.
|Relevant Fields||Archaeology, anthropology, art history, museum studies and management, park service interpretive programs, and nonprofit preservation projects|
|Research Issue||Documenting fragile, complex, and ancient rock drawings of all sizes, shapes, and inscription styles in challenging field conditions. The data collected must be scientifically rigorous, comprehensive, and useful for documentation, archiving, and presentation on the Web, in print, and in museum and park displays, kiosks, and interpretive programs.|
|Solution||CHI and Hewlett-Packard Laboratories (HP Labs) offer new imaging methods for capturing, processing, archiving, and presenting artifacts in the lab or in the field using readily available tools, software, equipment, and easy-to-learn techniques.|
|Benefits||High-quality, high-resolution image files can be adapted for many uses. CHI’s versatile techniques work with a variety of cameras, digital imaging equipment, and inexpensive tools. All of the gear needed is portable and can be hand-carried into rough terrain if necessary. Researchers, students, and cultural heritage (CH) staff can learn the techniques quickly and work on their own with little technical support. The process is designed to provide free detailed information to all via public-domain sharing technologies on the Web.|
Rescuing Remarkable Rock Art
A remote valley in Portugal contains a treasure trove of images from humanity’s distant past—Paleolithic petroglyphs in many shapes, sizes, and styles. The rugged, rocky terrain shelters at least 600 stone panels inscribed with thousands of drawings of animals, people, and symbols. These complex drawings were chipped and scratched into the rocks by humans living or traveling through the area as early as 22,000 years ago. Many of the drawings date from 14,000 to 12,000 years ago, and some are as recent as the 20th century.
Rare Rock Art Features
The Côa Valley is home to world-class rock art not found anywhere else on the planet. The Foz Côa site in one area of the valley is a refuge for the only known examples of “portable” rock art—small stones incised with animals. Some of the carved stones are only a few inches in size. Another interesting feature is the presence of “animated” rock art showing animals with two or three heads looking in different directions.
At one time, this incomparable valley was in danger of being submerged as part of a dam project, but local residents, high school students, and university scholars opposed the dam and saved the rock art. The Côa Valley is now a World Heritage Site with a planned visitor center and museum opening in 2008. In order to protect the unique rock art, park staff take care of the site and lead tours to the rock art areas accessible only with all-terrain vehicles or on foot.
Boosting Traditional Techniques With New Technology
|Working in the lab, capturing portable rock art||The highlight on the black ball is used to digitally document a portable petroglyph|
Computer science researchers from the Universidade do Minho, Dr. Alberto Proenca and Dr. Luis Paolo Santos, invited CHI co-founders Mark Mudge and Carla Schroer to visit the site and try their new tools. Prior to CHI’s arrival, Côa site researchers used painstaking traditional techniques to record the rock art designs with standard photographic methods and detailed drawings. The researchers look forward to adopting CHI's new techniques more widely.
While researchers can work with “portable” rock art in better conditions in the lab, the big rock panels cannot be moved. The scientists had to perform the time-consuming drawing and photography tasks at night and illuminate the rock art with floodlights. Parque Arqueologico do Vale do Côa (PAVC) and Centro Nacional de Arte Rupestre (CNART) staff often spend weeks on a single field drawing, dodging insects and other creatures that swarm to the lights at night, and they still may not capture all the rock art details. Because the site has such a long history, there are drawings scratched on top of older engravings, resulting in layers of important information that are difficult to record with standard photographs or illustrations.
Developing Tools the CHI Way
Mark Mudge, Carla Schroer, and CHI Imaging Director Marlin Lum collaborated with staff from the PAVC site and the CNART group, and scholars at the Universidade de Minho. Together, they collected digital image data to create 3-dimensional reflection transformation images (RTIs) of two types of rock art. They processed a “portable” petroglyph showing multiple animals, including an elegant deer drawing, in the lab to guide the Portuguese researchers in learning the CHI techniques. In the field, they collected data from an example of the “animated” rock art style—a two-headed goat looking forward and backward.
In the field, CHI personnel captured 60 images taken from different lighting directions in about a half an hour. The entire session took less than two hours to set up and take down gear and test the image files. The new techniques created images where layers of rock art from different eras are clearly defined. For the lab test, CHI staff showed their collaborators how to use the new methods with their existing gear in about half a day. The CHI “students” captured 60 images in about 20 minutes. They repeated the process to collect two more sets of data.
Capturing Beauty and Data
Both tests produced stunning interactive digital images. The interactive images allow viewers to drag the image in many directions to change the lighting, which snaps different surface details into sharp focus. The project produced data and image files containing incredible amounts of reputable information that the scientists can use in their research, publications, and presentations.
- SLR digital camera
- Light-reducing, neutral density filters
- Laptop computer with remote camera control software and Adobe Photoshop
- Radio flash trigger
- 1- to 1/32-power adjustable 320-watt second flash with battery pack
- Black ball on length- and angle-adjustable boom
- Measuring tape
- Retractable surveyor’s plumb-bob string (bob removed)
- Intensity-adjustable continuous light (optional, if power available)
Casting Light on the Future
CHI and its collaborators are planning to continue the work beyond this proof-of- concept project. They have submitted funding proposals proposals in both Europe and North America for continued development of the software tools to make them even easier to use. The team at the Park is eager to explore the technique on more panels and hopes to use the imaging technology in their planned visitor center to aid the public in seeing the fine details of this ancient art.
The CHI software needed to create images and to view them is available free for non-commercial use. Some software is open-source or public-domain.Polynomial Texture Mapping (PTM)
Image-based representation of the appearance of a surface under varying lighting directions. An early form of Reflectance Transformation Imaging (RTI).Reflectance Transformation Imaging (RTI)
Mathematical techniques to transform image reflection data to accommodate changing light directions and to enhance surface details. Developed for use with PTMs by Tom Malzbender and his colleagues at HP Labs.Highlight RTI
A modification of RTI methods to accommodate using a handheld light source without prior knowledge of its position. Knowledge of light positions is necessary to capture RTI 3D information. Tom Malzbender adapted his RTI calculations so that CHI researchers could use them to analyze specular highlights from a black sphere (the snooker ball) included in the image captured by a digital camera, to determine light locations after the the image capture session.
Related Publications and Links
- CHI Publication: “New Reflection Transformation Imaging Methods for Rock Art and Multiple-Viewpoint Display”
- UNESCO Prehistoric Rock-Art Sites in the Côa Valley, a World Heritage Site in Portugal
- HP Labs Polynomial Texture Mapping (PTM) research
Photographs of Côa Valley Rock Art
This is a beautiful book full of photographs of the Côa Valley site:
No tiempo sem tempo: A arte dos cacadores paleoliticos do Vale do Côa by Antonio Martinho Baptista, 1999, Centro Nacional de Arte Rupestre e Autor. ISBN: 972-98121-0-1.