Shedding New Light on Ancient Objects

Abstract

Shedding New Light on Ancient Objects BEN F. S. ALTSHULER THOMAS MANNACK While archaeology has often benefitted from expanded excavations and deeper trenches, the field is now entering an age in which the most spectacular finds are not coming out of the ground but out of existing museum collections. Digital Archaeology is allowing experts to uncover secrets in plain sight; indeed, to go beyond the boundaries of human sight to document sketch lines under layers of paint, transcribe badly eroded inscriptions, and recover the faintest palimpsests. With the power of these technologies growing exponentially, the next groundbreaking find could just as easily be discovered in the basement of a museum as under the streets of Naxos. Polynomial Texture Mapping (PTM) is a powerful computational photographic technology that is literally shedding new light on ancient objects. Its ability to analyze the smallest features of surface topology has led to breakthroughs in the fields of epigraphy, archaeology, and papyrology . The discoveries have been so frequent and significant that museums and archaeologists around the world are seeking to make PTM the standard international protocol for artifact documentation. More than anything else, it is the sheer volume of data gathered by PTM that sets it apart from what is currently the most common documentation method used in museums : simple photography. While a conventional photograph can adequately capture color information, it can only convey a very crude sense of shape and surface texture , primarily through depictions of highlights and shadows . By contrast, PTM, in addition to capturing superb arion 22.1 spring/summer 2014 color data, can also record detailed shape and texture measurements at the level of individual pixels. This massive quantity of incremental data not only provides a far more comprehensive method for object documentation than simple photography, it also opens up a range of opportunities for computer-driven rendering techniques—including potentially the use of 3d printers—for creating highly detailed depictions of objects for study and analysis . Although the PTM capture process requires precision and specialized equipment, it is completely non-invasive. This is an important virtue and accounts, in part, for its increasingly widespread adoption. Older methods—such as taking paint samples and squeezes—require extensive contact with an object and always present a risk of damage or wear. Since these destructive processes are antithetical to the preservation ethos of most museums, such techniques are used sparingly. For many fragile or important artifacts, the use of these processes is simply out of the question altogether. Consequently, many scholars have come to rely on PTM as a safe and thorough way of documenting an object. While no more harmful to an object than conventional photography, PTM provides far more topographical data than the destructive technologies of old. The fundamental concept underlying PTM technology could not be simpler. Indeed, anyone who has ever rotated an object in the sunlight to get a better view of its surface has employed the same principles on which PTM is based. PTM monitors and records the properties of both the incoming light striking an object and the reflection of that same light. Based on the relationship between the measured properties of the incoming and reflected light, the equipment can determine the precise surface structure of an object. In essence, PTM creates a topographical map of an object that shows even the most minute peaks and valleys —right down to faintest minim in a barely visible shedding new light on ancient objects 54 palimpsest. This is, in fact, precisely what your eye does every time you turn a worn coin in the light to read the date. PTM merely quantifies, records and maps the data for future reference and close examination. The PTM equipment also optimizes the lighting and capture technique to assure best results. The mechanical functionality of PTM is likewise straightforward. When using PTM to record the surface of an object, a sequence of images is captured in which camera and object are fixed in position relative to one another while a light source is moved around the object through a range of predetermined positions. A variety of specific capture techniques may be used consistent with this basic approach. One common technique employs a dome...