| Two-level Volume Rendering (2lVR) |
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In this paper we present a two-level approach for volume rendering, i.e., two-level volume rendering (2lVR), which allows for selecetively using different rendering techniques for different subsets of a 3D data-set. Different structures within the data-set are rendered locally on an object-by-object basis by either DVR, MIP, surface rendering, value integration (x-ray-like images), or non-photorealistic rendering. Globally all the results of subsequent object renderings are combined in a merging step (usually compositing in our case). This allows to selectively choose the most suitable technique for depicting each object within the data, while keeping the amount of information contained in the image at a reasonable level. This is especially useful when inner structures should be visualized together with semi-transparent outer parts, similar to the focus-plus-context approach known from information visualization. We also present an implementation of our approach, which allows to explore volumetric data using two-level rendering at interactive frame rates.
Two-level volume rendering (2lVR) is a result of joint work between visualization research in Vienna, Austria (H. Hauser, L. Mroz, M. E. Gröller), as well as mathematics research at Urbino unversity in Italy (G.-I. Bischi). Parts of this work have been carried out as part of the BandViz project, which is supported by FWF under project number P12811. Further parts of this work have been carried out as part of the basic research on visualization at the VRVis Research Center in Vienna, Austria, which is partialy funded by an Austrian governmental research program called Kplus. Acknowledgements also go to VisMed, a FFF-funded project, for the collaboration in the field of medical visualization.
A paper with title ``Two-level Volume Rendering'' (authored by Helwig Hauser, Lukas Mroz, Gian-Italo Bischi, and M. Eduard Gröller) is available as a technical report from VRVis. Another web page about two-level volume rendering is available from the Institute of Computer Graphics and Algorithms at Vienna University of Technology, Austria.
Left: DVR rendering.
Right: two-level volume rendering. Blood vessels inside the skull are equally visible throughout the image due to the uniform transparency of the MIP-rendered skull.
Left: DVR rendering.
Right: two-level volume rendering. The stenosis right inside the pelvis is equally visible from all sides.
Left: DVR rendering.
Right: two-level volume rendering. MIP rendering of the vertebrae allows to clearly see the embedding of the screws.
(to retrieve an enlarged version of the images, click on them):
Left: two-level volume rendering of a medical data-set; bones: DVR, vessels: surfaces, skin: NPR..
Right: DVR, surface rendering, and MIP combined; bones: DVR (sharp TF), vessels: surfaces, skin: MIP.
Below (a-f): different rendering techniques which can be combined using two-level volume rendering.
Below (a-c): three comparisons between traditional rendering (bottom line) and two-level volume rendering (top line); the above displayed animation sequences correspond to the below images.
Below (a-c): three examples of two-level volume rendering applied to complex dynamical systems:
Below (a-c): three further results computed with two-level volume rendering:
In case of questions, comments, etc., please mailto:Hauser@VRVis.at.