This project studies the process of visualizing information at every point in space through volume rendering. Traditionally, volume rendering has employed one of two approaches. The first attempts a physically accurate simulation of a process such as X-rays passing through tissue or light passing through a fog, producing the most realistic views of volume data (at least for data with an appropriate physical meaning). The second approach is only loosely based on the physical behavior of light, using instead an arbitrary appearance of each value in space and an accumulation process through space to create a wider range of appearances for the volume in the visualization. This project proposes a new approach to volume rendering: the augmentation of a physics-based rendering process with non-photorealistic rendering (NPR) techniques to enhance the expressiveness of the visualization. NPR draws inspiration from such fields as art and technical illustration to develop automatic methods to synthesize images with an illustrated look from geometric surface models. The new approach, called volume illustration, combines the familiarity of a physics-based illumination model with the ability to enhance important features using non-photorealistic rendering techniques.
Technically, the project faces several challenges. In surface-based NPR, the surfaces (features) are well defined, whereas with volumes, volumetric feature areas are often amorphous regions that must be determined through analysis of local volumetric properties. Once these volumetric feature volumes are identified, user selected parametric properties can be used to enhance and illustrate them. Volume illustration provides a flexible unified framework for enhancing structural perception of volume models through the amplification of features, the addition of illumination effects, and the application of procedural textures. Volume illustration will work on both presampled and procedurally defined volume models, enabling a range of image styles from practical technical illustrations to more abstract painterly effects. The project will develop a collection of volume illustration techniques, including novel volume illustration techniques and techniques that adapt and extend NPR techniques to volume objects.
