New Reflection Transformation Imaging Methods for Rock Art and Multiple-Viewpoint Display

Abstract

We offer two new methods of documenting and communicating cultural heritage information using Reflection Transformation Imaging (RTI). One imaging method is able to acquire Polynomial Texture Maps (PTMs) of 3D rock art possessing a large range of sizes, shapes, and environmental contexts. Unlike existing PTM capture methods requiring known light source positions, we rely on the user to position a handheld light source, and recover the lighting direction from the specular highlights produced on a black sphere included in the field of view captured by the camera. The acquisition method is simple, fast, very low cost, and easy to learn. A complementary method of integrating digital RTI representations of subjects from multiple viewpoints is also presented. It permits RTI examination in the round in a unified, interactive, image-based representation. Collaborative tests between Cultural Heritage Imaging, Hewlett- Packard Labs, and the UNESCO Prehistoric Rock-Art Sites in the Côa Valley, a World Heritage Site in Portugal, suggest this approach will be very beneficial when applied to paleolithic petroglyphs of various sizes, both in the field and in the laboratory. These benefits over current standards of best practice can be generalized to a broad range of cultural heritage material.