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Cohen, MF

1992

Volume Seedlings

Cohen, M.F.; Painter, J.S.; Mehta, A.K. and Ma, K.-L.
ACM Symposium on Interactive 3-D Graphics, Cambridge, MA, March 1992. Funded by International Business Machines and ACERC.

Recent advances in software and hardware technology have made direct ray-traced volume rendering of 3-d scalar data a feasible and effective method for imaging of the data's contents. The time costs of these rendering techniques still no not permit full interaction with the data, and all of the parameters affecting the resulting images. This paper presents a set of real-time interaction techniques that have been developed to permit exploration of a volume data set. Within the limitation of a static viewpoint, the user is able to interactively alter the position and shape of an area of interest, and modify local viewing parameters. A run length encoded cache of volume rendering samples provides the means to rerender the volume at interactive rates. The use locates and plants "seeds" in areas of interest through the use of data slicing and isosurface techniques. Image processing techniques applied to volumes (i.e. volume processing), can then automatically form regions of interest that in turn modify the rendering parameters. This "region growing" of "seedlings" incrementally alters the image in real-time providing further visual cues concerning the contents of the data. These tools allow interactive exploration of internal structures in the data that may be obscured by other imaging algorithms. Magnetic Resonance Angiography (MRA) provides a driving application for this technology. Results from preliminary studies of MRA data are included.

1991

Volume Seeds: A Volume Exploration Technique

Ma, K.-L.; Cohen, M.F. and Painter, J.S.
Journal of Visualization and Computer Animation, 1991 (in press). Funded by ACERC.

Ray-traced volume rendering has been shown to be an effective method for visualizing 3-D scalar data. However, with currently available workstation technology, interactive volume exploration using conventional volume rendering is still too slow to be attractive. This paper describes an enhanced volume rendering method that allows interactive changes of rendering parameters such as color and opacity maps. An innovative technique is provided which allows the user to plant a "seed" in the volume to rapidly modify local shading parameters. For a fixed viewing position, the user can interactively explore specific regions of interest. Furthermore, a virtual cutting technique with the exploratory seed allows the user to remove surfaces and see the internal structure of the volume. Examples demonstrate these techniques as an attractive option in many applications.