Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1997-12-19
2001-05-15
Powell, Mark R. (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C345S156000
Reexamination Certificate
active
06232979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computer data processing and graphics, and in particular, to computational tasks including, but not limited to, volume rendering and image processing operations.
2. Related Art
Three-dimensional arrays of digital data representing spatial volumes arise in many applications. Computed tomography (CT) and magnetic resonance (MR) scanners create a volume by imaging a series of cross-sections, also called slices. Astrophysical, meteorological, and geophysical measurements, and business or economics data also naturally lead to a volume data set. Computer graphics systems use a volume rendering algorithm to display a visualization of a volume. See, R. Drebin, L. Carpenter, and P. Hanrahan, “Volume Rendering,”
Computer Graphics
, Vol. 22, No. 4, (SIGGRAPH '88, Atlanta, Ga.), August 1988, pp. 65-74 (incorporated in its entirety herein by reference); and B. Cabral, N. Cam and J. Foran, “Accelerated Volume Rendering and Tomographic Reconstruction Using Texture Mapping Hardware,”
Proceedings of ACM/IEEE Symposium on Volume Visualization
(IEEE CS Press), pp. 91-98, 1994 (Order No. PR07067, 1995)(incorporated in its entirety herein by reference); and the co-pending, commonly-owned U.S. patent application by B. Cabral and J. Foran, “
A System and Method of Performing Tomographic Reconstruction and Volume Rendering Using Texture Mapping
,” filed Jul. 7, 1995, Appl. Ser. No. 08/499,614 (SGI Ref. No. 15-4-148.00, SKGF Ref. No. 1452.0420000) (incorporated in its entirety herein by reference).
In computer graphics platforms, the re-sampling speed limits fast volume-rendering. For example, one common volume rendering approach uses maximum intensity projection for volume rendering. In one implementation of this type of volume rendering, slices Si are first assumed to be parallel to a viewpoint. For example, as shown in
FIG. 1
, eight slices S1 to S8 can be used as a volume data set. Slices S1 to S8 each have m bits of grey-scale channel data representing corresponding MR scan cross-section images. For example, grey-scale data can represent pixel intensity ranging from black to white using a single digital value, such as 0 to 256, where 0 represents black and 256 represents white and 1 to 255 represent progressive intermediate shades of grey.
Each slice S1 to S8 is then loaded as a separate one-channel luminance texture (total 8 one-channel textures). The textures for slices S1 to S8 are then drawn on top of each other successively using blending. For example, in a system supporting a graphics application programming language, such as OpenGL™ manufactured by Silicon Graphics, Inc., a blending function can be set to draw each slice one on top of the other. Consequently, resampling is performed for each slice in succession and the result is stored in a frame buffer prior to being displayed. Each successive resampling operation which must be performed slows overall volume rendering time.
What is needed is a method, system and computer program product for fast computation that increases resampling and blending speed. The number of successive resampling operations which must be performed needs to be reduced.
SUMMARY OF THE INVENTION
A method, system, and computer program product are provided for fast computation using parallel resampling and blending in multi-channel texture mapping. According to one embodiment of the present invention, slices of projection data for volume rendering are loaded into multiple textures. The loaded textures are combined using multi-channel texture mapping to obtain a multi-channel data frame for storage in a multi-channel frame buffer. Preferably, the multiple textures are combined using a texture mapping operation that includes a linear blending operation, such as, a maximum, minimum, and/or sum blending operation. Multi-channel frame buffer data is then aggregated to obtain a final single channel grey-level output of pixel data.
In one example implementation of the present invention, a load unit loads slices of projection data into multiple textures. A multi-channel texture engine combines the multiple textures to obtain multi-channel frame data for storage in a multi-channel frame buffer. Preferably, the texture engine performs a texture mapping operation using a linear blending operation, such as, a maximum, minimum, and/or sum blending operation. An aggregation unit, such as a summer unit, aggregates the multi-channel frame buffer data to obtain a final single channel grey-level output of pixel data.
For example, eight slices of maximum intensity projection volume data can be loaded into two four-channel textures, e.g., two RGBA (red, green, blue, alpha) textures. Two RGBA textures are combined into a single multi-channel data frame using parallel multi-channel texture mapping. A linear blending function can be set to a maximum (or minimum) and sum function. The result is that after texture mapping, each red, green, blue and alpha channel in the frame buffer will contain pixel data representing the maximum of two corresponding slices. An aggregation operation is then performed on each RGBA channel in the frame buffer to obtain a final single channel grey-level output.
The present invention leverages the parallel resampling and blending operations available in multi-channel texture engines so that fewer resampling operations are required in volume rendering of projection data or any other computational task. For example, the present invention decreases the number of resampling operations by a factor of four in the case of volume rendering of eight slices of projection data using a four-channel texture engine. In other words, the present invention improves resampling speed approximately four-fold in the case of volume rendering of eight slices of projection data using a four-channel texture engine.
The present invention is described primarily with respect to an example volume rendering embodiment. As would be apparent to a person skilled in the art given this description, the present invention can be used for any computational task including, but not limited to, fast volume rendering and image processing. The present invention can be used on any type of single channel or dual-channel data. In other words, any single or dual channel data can be loaded or split into multi-channel texture data and then rendered, image-processed, blended, and/or accumulated. The final result is then aggregated back into the original number of channels, e.g. back into single channel or dual channel data.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
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Foley,Computer Grahics, Addison-Wesley Publishing, 1996, pp. xvii-xxiii and 855-922.
Cabral et al., “Accelerated Volume Rendering and Tomographic Reconstruction Using Texture Mapping Hardware”, Proceedings of ACM/IEEE Symposium on Volume Visualization (IEEE CS Press), 1994, pp. 91-98.
Drebin et al., “Volume Rendering”,Computer Graphics, vol. 22, No. 4, Aug. 1988, pp. 65-74.
Azevedo, Stephen G., Brian K. Cabral and James Foran, Silicon Graphics Computer Systems, “Tomographic image reconstruction and rendering with texture-mapping hardware”, SPIE vol. 2299, pp. 280-291.
The Cube Project (visited Jan. 21, 2000), <http: //www.cs.sunysb.edu/-vislab/projects/cube/cube. html>, 1 page.
Motivation (visited Jan. 21, 2000), <http: //www.cs.sunysb.edu/-vislab/projects/cube/motivation.html>, 3 pages.
Cube Project -Publications (visited Jan. 21, 2000), <http: //www.cs.sunysb.edu/-vislab/projects cube/cubePapers.html>, 4 pages.
Osborne
Nguyen Thu
Powell Mark R.
Silicon Graphics Inc.
Sterne Kessler Goldstein & Fox P.L.L.C.
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