Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Patent
1997-05-28
1999-08-03
Powell, Mark R.
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
345426, G06T 1700
Patent
active
059331461
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of, and apparatus for, constructing an image of a notional scene. The invention is particularly concerned with the construction of images by a process of ray tracing.
BACKGROUND TO THE INVENTION
Ray tracing is one of a number of processes by which a computer can generate an image of a notional scene containing, for example, one or more objects illuminated by one or more localised light sources, or by ambient light.
The ray tracing process determines, for each pixel to constitute the image, whether any light rays would pass from the scene through the co-ordinates defining the position of the pixel relative to the scene and to a notional viewing position. The contributions made by any such rays to the notional intensity and colour of light incident on the viewing position are then calculated. This information determines the required brightness and colour for the pixel. A basic ray-tracing method is described in the article entitled "An Improved Illumination Model for Shaded Display", in Communications of the ACM, 26 (6), 342-349 (Whitted 1980).
Ray tracing enables a high resolution of image to be created, and can depict phenomena such as reflection, refraction and light scattering.
However, a large number of calculations have to be performed in order to determine the path (and characteristics) of each light ray, as a result of which a ray tracing method tends to be very slow.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of constructing an image of a notional scene, containing a plurality of objects, as viewed from one of a plurality of possible viewing positions and illuminated in a known manner, from information on the co-ordinates of the surfaces of the objects, on the optical characteristics of all the points on those surfaces and on the particular illumination, which information is stored in a computer memory, the method comprising:
A. Projecting from the viewing position a plurality of straight line paths and storing data describing all said paths;
B. For one of the objects, determining which, if any, of the straight line paths intersect a surface of the object or a zone of illumination and for each intersecting path determining the co-ordinates of the intersection nearest the viewing position and storing all said intersections;
C. Repeating step B above for the other object or for each other object in turn;
D. Determining, for each path, the nearest intersection to the viewing position and storing same with data on the object surface at that intersection;
E. Determining, for the stored surface data, the light which will pass along the path to the viewing position for each said nearest intersection and storing same as light intensity and position data; and
F. Reading out the stored light intensity and position data to produce a picture signal display on a visual display.
Since all of said plurality of the straight line paths are considered in relation to the or each subset in turn, details of the surfaces in each subset only have to be retrieved from the memory once in order to determine all the intersections of those straight line paths with those surfaces. Consequently the number of times that details of surfaces have to be retrieved from the memory and hence the associated time delay, is minimised, as a result of which the ray tracing method can be performed more rapidly than known methods in which details of each surface have to be retrieved at least once per path.
Said plurality of straight line paths might be just some, but preferably constitute all, of the straight line paths needed to construct the image.
Preferably, each subset contains the surfaces of a respective one of the objects.
Preferably step E above involves projecting a set of one or more secondary straight line paths from the intersection, if the characteristics of the object surface at the intersection are such that light, if incident on the interface along a direction defined by the/or each secondary path, would be at le
REFERENCES:
patent: 4928250 (1990-05-01), Greenberg et al.
patent: 5485556 (1996-01-01), Takagi et al.
patent: 5583975 (1996-12-01), Naka et al.
Advanced Rendering Technology Limited
Cao Huedung X.
Powell Mark R.
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