The application of direct volume visualization techniques to the presentation of CT data is explored. No surface detection or fitting of geometric primitives is involved. Images are formed by directly shading each data sample and projecting it onto the picture plane. The visualizations in this study are based on a hybrid physical model incorporating aspects of both surfaces and semi-transparent gels. Using a surface model, shading calculations are performed at every voxel with local gradient vectors serving as surface normals. In a separate step, surface classification and enhancement operators are applied to obtain a partial opacity for every voxel. Independence of shading and classification calculations insures an undistorted presentation of 3-D shape. The use of non-binary classification operators insure that small or poorly defined features are not lost. The resulting colors and opacities are merged from back to front along view rays using volumetric compositing, an approximation to the visibility calculations required to render a semi-transparent gel. The technique is simple and fast, yet produces images exhibiting smooth surface silhouettes and few other aliasing artifacts. The use of selective blurring and super-sampling to further improve image quality is also described.
[1]
M. Evoy,et al.
Rendering of Surfaces from Volumetric Data
,
1987
.
[2]
James F. Blinn,et al.
Light reflection functions for simulation of clouds and dusty surfaces
,
1982,
SIGGRAPH.
[3]
Marc Levoy,et al.
Rendering of Surfaces from Volume Data
,
1988
.
[4]
R. Bernstein,et al.
Shading 3D-Images from CT Using Gray-Level Gradients
,
1986,
IEEE Transactions on Medical Imaging.
[5]
Francis Schmitt,et al.
Active-Ray Tracing for 3D Medical Imaging
,
1987,
Eurographics.
[6]
Alvy Ray Smith,et al.
3-D transformations of images in scanline order
,
1980,
SIGGRAPH '80.
[7]
Tom Duff,et al.
Compositing 3-D rendered images
,
1985,
SIGGRAPH.
[8]
Tom Duff,et al.
Compositing digital images
,
1984,
SIGGRAPH.
[9]
G. Herman,et al.
Three-dimensional display of human organs from computed tomograms
,
1979
.
[10]
Bui Tuong Phong.
Illumination for computer generated pictures
,
1975,
Commun. ACM.
[11]
William E. Lorensen,et al.
Marching cubes: A high resolution 3D surface construction algorithm
,
1987,
SIGGRAPH.
[12]
Arie E. Kaufman,et al.
Voxel-Based Architecture for Three-Dimensional Graphics
,
1986,
IFIP Congress.