Many fossils cannot be fully illustrated using a setting of physical light sources, and conventional photographic approaches are therefore insufficient. Polynomial texture mapping (PTM), a new technique for imaging surface relief using an ordinary digital camera and multiple light sources, offers an opportunity to resolve these difficulties. In PTM, a series of 50 pictures is taken with the specimen and camera in fixed positions, but with varying directions of incoming light. These pictures are converted digitally into a PTM file, incorporating information about the reflectance of each pixel under different lighting conditions. The number, position, and intensity of virtual light sources can then be manipulated, as can the reflectance properties of the imaged surface. In addition to bringing out low surface relief that may otherwise be difficult to illustrate, PTM also allows electronic transfer, storage, and publication of images, allowing users to manipulate virtual light sources interactively. Herein we test this technique using fossils with different types of preservation, including Cambrian fossils from the Burgess Shale and Chengjiang conservation lagerstätten, Cambrian fossils with 3D relief from dark shales of Norway, Carboniferous plant fossil impressions from England, Cambrian trace fossils in sandstone from Sweden, and Neoproterozoic impression fossils from the Ediacara lagerstätten of south Australia. Whereas not optimal for all types of fossil preservation, PTM enhancement techniques can provide noticeable improvement in the imaging of specimens with low color contrast and low but definite relief. The imaging of specimens with higher relief, although they can be easily photographed with traditional techniques, will still benefit from PTM because of the opportunity of interactive manipulation of light and reflectance.
Øyvind Hammer. Geological Museum, Boks 1172 Blindern, 0318 Oslo, Norway.
Stefan Bengtson. Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden.
Tom Malzbender. HP Labs, 1501 Page Mill Road, Palo Alto, CA 94304-1126, USA.
Dan Gelb. HP Labs, 1501 Page Mill Road, Palo Alto, CA 94304-1126, USA.
KEY WORDS: photography, image enhancement, surface relief, interactive visualization, polynomial texture mapping
Association 23 August 2002
Submission: 18 April 2002 Acceptance: 9 August 2002