An alternative approach for illustration of low-contrast fossils with minor surface relief is to use a high-precision laser scanner (Lyons et al. 2000). Using such a technique, the elevation data from the scanner can be amplified or surface normals estimated for the purpose of specular enhancement or diffuse gain. However, for small surface relief and high image resolution, a very sophisticated and expensive scanner is needed. In contrast, the photographic apparatus necessary for the PTM technique can be constructed for less than 2000 US dollars. Spatial resolution is also compromised by using a laser scanning system, because the computation of geometric surface normals requires convolution with a kernel having spatial extent. In the case of PTM , normal estimation for each pixel is performed independently.
In addition to image enhancement, the PTM technique involves an efficient set of acquisition techniques and a file format for the electronic publishing of fossil images where virtual lighting can be freely manipulated. Considering how morphological features of a single fossil specimen are differentially enhanced in a dramatic way depending on lighting, this has the potential of greatly increasing the information content of paleontological images.
The PTM technology is a relatively simple and inexpensive new tool for paleontological illustration, to be used in addition to or in combination with existing photographic techniques. Compared with other methods, it provides the best results for specimens with little color contrast and small but definite relief, but its interactiveness is useful for all types of specimens.