Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1998-04-03
2001-07-31
Vo, Cliff N. (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
Reexamination Certificate
active
06268860
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority of Patent Application Ser. No. 197 14 915.4, filed Apr. 3, 1997, in the Federal Republic of Germany, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an imaging method and apparatus for displaying computer-modeled objects present in the form of a grid model, in which the objects are defined by the coordinates of the node points of the grid model and the optical properties of the polygon surfaces between the node points, and the individual polygon surfaces are divided into a plurality of scanlines and pixels. The image impression is calculated in only a portion of the pixels according to a local illumination model, or a portion of a local illumination model, and is interpolated in the remaining pixels from the previously-calculated image-information values for reducing the calculation effort.
In computer-graphics systems, objects are usually simulated with grid models, in which the objects are defined by the spatial coordinates of the node points of the grid model and the optical properties, such as the color and reflection behavior, of the polygon surfaces between the node points. Computer-graphics systems of this type are known from, for example, VOORHIES, D.; FORAN, J.: Reflection Vector Shading Hardware, SIGGRAPH ′94, and JACKÈL, D.; Rüsseler, H.:A Real Time Rendering System with Normal Vector Shading; 9th Eurographics Workshop on Graphics Hardware, Oslo (Norway), 1994. To calculate the image impression, the individual polygon surfaces are divided into pixels, and the spatial coordinates and the spatial position of the local surface normal, which are decisive for the reflection behavior and thus the impression of the image, are calculated for each pixel. With an inclination of the local surface normal inside the polygon surface, for example, it is also possible, on the one hand, to simulate curved polygon surfaces, so a smooth and thus visually inconspicuous transition can be attained at the edges between adjacent polygon surfaces. On the other hand, it is also possible to simulate rough textures in this manner by inclining the local surface normal inside the respective polygon surface to correspond to the desired texture, which is also referred to as bump-mapping. After the spatial coordinates of the individual pixels and the respective local surface normal have been calculated, the image impression is calculated individually for each pixel, according to a local illumination model; the perspective of the viewer, the spatial position and the optical properties of the pixel, the orientation of the local surface normal and the spatial position and optical properties of the light sources that illuminate the objects are all considered.
Typically, the illumination model used to calculate the image impression of the individual pixels is the one described in PHONG: Illumination for Computer Generated Pictures; Communications of the ACM, 18(6):311-317, June 1975, which has also been incorporated into the quasi-industry standard OpenGL. This illumination model advantageously permits the consideration of numerous optical effects, such as ambient, diffuse and specular reflection, and thus produces a very realistic image impression.
A disadvantage of the known imaging methods based on a local illumination model is the relatively large amount of calculation effort. In a software-based solution, the serial processing of the calculation steps increases the time span necessary for calculating an image, which hinders a real-time display of representations of movement, particularly with complex illumination relationships. In a hardware-based solution, the increased calculation effort can be overcome with a plurality of pipelines operating in parallel, but this arrangement is associated with a larger chip surface.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide an imaging method of the above-described type and an apparatus for executing the method, in which the image impression is calculated according to a local illumination model, and the calculation effort is reduced, so the imaging method can also be executed with relatively simple hardware, or even complex scenes with a plurality of light sources can be calculated sufficiently quickly.
The object is accomplished by providing an imaging method and apparatus for displaying computer-modeled objects that are present in the form of a grid model and are simulated by a plurality of adjacent polygon surfaces, in which a first assembly of a calculation unit calculates a plurality of first coordinate sets from a first parameter set that respectively represents the spatial position of one of the polygon surfaces, the coordinate sets respectively representing the spatial position of a pixel of the respective polygon surface, a second assembly of the calculation unit uses the first parameter set representing the spatial position of the polygon surface to calculate a second coordinate set for each pixel of the polygon surface, which set represents the spatial position and direction of the local surface normal, a third assembly of the calculation unit uses a second parameter set representing the spatial position and the optical properties of at least a first light source, as well as the first coordinate sets representing the spatial position of the individual pixels, and the second coordinate sets representing the spatial position of the local surface normals, to calculate image-information values according to a local illumination model, the values representing the image impression of a respective pixel, and a fourth assembly of the calculation unit uses the first coordinate set representing the spatial position of the respective pixel to calculate a two-dimensional screen-coordinate set for each pixel for display on the screen, which set determines the position of the pixel on the screen. A first portion is selected from all of the pixels of the respective polygon surface, and the third assembly calculates of the image-information values for all of the pixels of the first portion according to the local illumination model or a portion of the local illumination model, and subsequently a fifth assembly uses the image-information values that have been calculated for the first portion of pixels to interpolate the image-information values for a second portion of pixels that includes the remaining pixels of the polygon surface.
The invention includes the technical teaching of calculating the image impression for only a portion of the pixels within a polygon surface, according to a local illumination model, for saving calculation time and/or reducing the hardware prerequisites, and interpolating the image impression for the remaining pixels from the previously calculated image-information values.
The term “local illumination model” is not limited here or hereinafter to the aforementioned and preferably used Phong illumination model, but, in principle, also encompasses other illumination models that permit the calculation of the image impression of a pixel of a polygon surface as a function of the illumination relationships and the geometrical relationships.
The measures employed in the invention can be implemented with both purely software-based measures and suitable special hardware. Within the framework of a hardware-based solution, it is also possible to switch a plurality of so-called pipelines in parallel, in which the respective image impression of a pixel is calculated. Pipelines of this type are arithmetic and logical units comprising assemblies switched one behind the other and separated by storage elements, with a plurality of intermediate results being located in the assemblies simultaneously (in parallel) during different calculation phases. With each cycle, all of the intermediate results advance by one calculation step, so one end result can be attained per cycle. “Pipelining” of this nature can significantly shorten the time span required for calculating an
GMD-Forschungszentrum Informationstechnik GmbH
Kinberg Robert
Spencer George H.
Venable
Vo Cliff N.
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