Transparency can be a useful device for depicting multiple overlapping surfaces in a single image. The challenge is to render the transparent surfaces in such a way that their three-dimensional shape can be readily understood and their depth distance from underlying structures clearly perceived. This paper describes our investigations into the use of sparsely-distributed discrete, opaque texture as an "artistic device" for more explicitly indicating the relative depth of a transparent surface and for communicating the essential features of its 3D shape in an intuitively meaningful and minimally occluding way. The driving application for this work is the visualization of layered surfaces in radiation therapy treatment planning data, and the technique is illustrated on transparent isointensity surfaces of radiation dose. We describe the perceptual motivation and artistic inspiration for defining a stroke texture that is locally oriented in the direction of greatest normal curvature (and in which individual strokes are of a length proportional to the magnitude of the curvature in the direction they indicate), and discuss two alternative methods for applying this texture to isointensity surfaces defined in a volume. We propose an experimental paradigm for objectively measuring observers' ability to judge the shape and depth of a layered transparent surface, in the course of a task relevant to the needs of radiotherapy treatment planning, and use this paradigm to evaluate the practical effectiveness of our approach through a controlled observer experiment based on images generated from actual clinical data.
|Original language||English (US)|
|Number of pages||20|
|Journal||IEEE Transactions on Visualization and Computer Graphics|
|State||Published - 1997|
Bibliographical noteFunding Information:
The work described in this paper was supported by U.S. National Institute of Health grant # PO1 CA47982, and was performed as a part of the dissertation research of the first author, who received valuable advice in this effort from Frederick Brooks, Christina Burbeck, Julian Rosenman, and Mary C. Whitton. We are very grateful to Dr. Ron Nowaczyk for assisting us in performing the statistical analysis of the experimental results. Marc Levoy provided the volume rendering platform within which we implemented the isosurface extraction and surface texturing functions, and Jim Chung provided the implementation of the marching cubes algorithm that we adapted for the surface triangulation. The radiation therapy data was provided by Dr. Julian Rosenman, UNC Hospitals. The preparation of this paper was supported by the National Aeronautics and Space Administration under NASA contract number NAS1-19480 while the first author was in residence at ICASE.
- Principal direction texture
- Shape and depth perception
- Shape representation
- Transparent surfaces