Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1998-10-15
2001-04-17
Vo, Cliff N. (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
C345S427000
Reexamination Certificate
active
06219060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rendering three-dimensional surfaces from volumetric data.
2. Description of Related Art
Regularly spaced volumetric data acquired from various sources such as computer tomography (CT), magnetic resonance (MR) imaging, ultrasound, and various other imaging means defines volume pixels or ‘voxels’ between the data. The data values represent a physical aspect of the object being imaged at a number of locations throughout the imaging volume. Typically these values change significantly at interfaces between different types of material. These interfaces may be visualized as surfaces. Besides indicating the interface of two materials, as in the case in medical imaging, they may be arbitrary thresholds as in the case of temperature differences, indicating isotherms or pressure differences indicating isobars of weather data. For whatever use, it is important to visualize surfaces within a block of volumetric data.
Many times the spacing between adjacent measurement points is different from the spacing between layers of adjacent measurements. For example, data values having equal spacing between adjacent values and between layers would have an aspect ratio of (length; width; height) of (1:1:1). An aspect ratio for measurements having equal spaces between adjacent measurements but twice the distance between layers would have an aspect ratio of (1:1:2). Since many systems employ the same spacing between adjacent data values in a “layer” but a different spacing between layers of data, the measurements may be described by an ‘aspect ratio’ A, being the relative spacing of the long dimension(s) to the short dimension(s), such as A=2, in the above example.
U.S. Pat. No. 4,719,585, Jan. 12, 1988, Cline et al. “Dividing Cubes System and Method for the Display of Surface Structures Contained Within the Interior Region of a Solid Body” (“Dividing Cubes”) describes a method of determining surfaces in volumetric data and rendering those surfaces. An objective of the ‘dividing cubes’ patent is to break up the voxels of the volumetric data into successively smaller voxels and to interpolate intervening values in three dimensions. This employed tri-linear interpolation, to create other intervening values. Tri-linear interpolation typically is computationally expensive and slows the process down. This method would be faster if there were no tri-linear interpolation.
In many types of rendering and imaging it is important to quickly render surfaces. Dividing cubes is most efficient when the aspect ratio are integral numbers. For example an aspect of ratio of A=4 would be computationally less expensive than a fractional ratio such as A=4.36. This is because their fractional aspect ratios require floating point math.
The ‘stretching cubes’ application referenced above describes another method of dealing with anisotropic volumetric data. In stretching cubes the order of rotation and scaling is reversed to eliminate the need for 3D interpolation. Interpolation occurs in 2 dimensions on the 2D-screen image. An isotropic volumetric data set is treated as if it were isotropic with an aspect ratio A=1. The model is rotated and rendered into a two dimensional screen space producing a data for a distorted 2D-screen image.
Knowing beforehand the aspect ratio A and the angles at which the model is to be rendered, it is a simple geometry problem to work backwards to determine the degree which the 2D screen image is distorted. The 2D-screen image is then ‘distorted’ in a direction opposite to the calculated distortion based upon the rendering angles and the aspect ratio of the original data. This may be done quickly since it is applied in two dimensions.
However, the resolution of the resulting 2D-screen image is dependent upon the viewing angle of the image. Since it is ‘stretched’ more in one dimension than another, the resolution suffers depending upon the selected viewing angle.
Currently there is a need for a rapid and high-resolution method of rendering surfaces from anisotropic volumetric data.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a simplified method rendering anisotropic volumetric data.
It is another object of the present invention is to provide a method of rendering anisotropic volumetric data more rapidly than was previously possible.
Another object of the present invention is to provide a higher resolution surface image from anisotropic volumetric data for a given degree of computation.
SUMMARY OF THE INVENTION
In this process, anisotropic data having an aspect ratio of A is modified into approximate anisotropic data. This is performed by interpolating equally spaced layers of data between existing layers. This is most preferably done by reducing the spacing by a reduction factor R=1/2
n
(n=1, 2, 3 . . . ). This is equivalent to halving the spacing until the new, modified aspect ratio A′ closest to unity results. This is similar to the ‘Dividing Cubes’ method.
In the second phase of the present invention, an image is created of the approximate isotropic data rendered as if it were isotropic data.
This 2D-screen image is then ‘stretched’ according to its rendered angle, similar to the ‘Stretching Cubes’ method. The approximate isotropic data is still anisotropic, however, the modified aspect ratio A′ is closer to unity. Therefore, there is less ‘stretching’ of the rendered 2D image, as performed by the ‘Stretching Cubes’ method, and will not significantly reduce the resolution of the image.
REFERENCES:
patent: 4719585 (1988-01-01), Cline et al.
patent: 5226113 (1993-07-01), Cline et al.
patent: 5781194 (1998-07-01), Ponomarev et al.
patent: 5841892 (1998-11-01), Mcgrath et al.
patent: 5963211 (1999-10-01), Oikawa et al.
patent: 6040835 (2000-03-01), Gibson
patent: 6054992 (2000-04-01), Gibson
patent: 6084979 (2000-07-01), Kanade et al.
Cline Harvey Ellis
Ludke Siegwalt
General Electric Company
Snyder Marvin
Testa Jean K.
Vo Cliff N.
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