Suppose the World was Piecewise Plastic?

Is it ridiculous to think of the world has nothing but plastic? That is precisely an assumption most volume renders make by using the Phong illumination model. Direct volume rendering has proven to be an effective and flexible visualization method for interactive exploration and analysis of 3D scalar fields. While widely used, most if not all applications render (semi-transparent) surfaces lit by an approximation to the Phong local surface shading model. This model renders surfaces simplistically (as plastic objects) and does not provide sufficient lighting information for good spatial acuity. In fact, the constant ambient term leads to misperception of information that limits the effectiveness of visualizations. Furthermore, the Phong shading model was developed for surfaces, not volumes. The model does not work well for volumetric media where sub-surface scattering dominates the visual appearance (e.g. tissue, bone, marble, and atmospheric phenomena). As a result, it is easy to miss interesting phenomena during data exploration and analysis. Worse, these types of materials occur often in modeling and simulation of the physical world. Physically correct lighting has been studied in the context of computer graphics where it has been shown that the transport of light is computationally expensive for even simple scenes. Yet, for visualization interactivity is necessary for effective understanding of the underlying data. We seek increased insight into volumetric data through the use of more faithful rendering methods that take into consideration the interaction of light with the volume itself.