Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Patent
1998-05-13
2000-10-10
Nguyen, Phu K.
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
G06F 1500
Patent
active
06130669&
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to an image-processing method for simulating a structure in relief in representing objects that particularly comprise at least one polygon surface, as defined in the preamble to claim 1, and an image-processing apparatus, as defined in the preamble to claim 11, for executing the image-processing method.
In computer-graphics systems, bodies are usually simulated by grid models. Each body is described by the spatial coordinates of the node points of the grid model. For display on a screen, the spatial coordinates from the three-dimensional coordinate system are converted, for example through central projection, into a two-dimensional screen-coordinate system.
The surface elements between the node points are usually represented as ideally smooth surfaces without uneven areas. Natural surfaces are, however, not smooth, but are relatively uneven and structured. For example, the surface of human skin has a fine porous structure. The surfaces represented with conventional computer-graphics systems are therefore perceived as unnatural by the viewer. To create a natural surface impression, the grid model would have to be refined so extensively that the spacing between the node points would be smaller than the uneven areas to be modeled. This would place significantly more demanding requirements on the storage capacity and computing capability of the computer-graphics system.
A method of simulating a relief structure in representing such surfaces is known from CATMULL, E. E.: Computer Display of Curved Surfaces, Proc. IEEE Conf. on Computer Graphics, Pattern Recognition and Data Structures, Los Angeles (May 1975), 11. In this case, a two-dimensional image of the desired relief structure--hereinafter referred to as texture image--is superposed over each surface element of the grid model. The brightness of a surface element is not consistent, but varies within the surface element corresponding to the texture image.
If the viewer looks at the surface element from the same direction from which the texture image was also received, and if the illumination is also the same as in the receiving of the texture image, the viewer obtains a natural visual impression of the relief structure of the surface.
In this case, the viewer always perceives the same texture image, regardless of the perspective and the illumination direction. The dependencies on the angle and direction of the reflection behavior of the relief structure of a natural surface are therefore not simulated in this method. The surface thus appears as a smooth surface onto which only a type of photo is placed. Such representations have an unnatural effect similar to that of objects to which a decorative sheet is affixed to give the appearance of a surface structure.
A method of simulating a relief structure in representing surfaces, which also takes into consideration the perspective of the viewer and the illumination direction, is further known from BLINN, J. F.: Simulation of Wrinkled Surfaces, Computer Graphics, 12(3), pp. 286-292, Proc. SIGGRAPH '78.
In this method, the surface normal that is decisive for the reflection behavior of the surface element is first calculated for each surface element. Furthermore, a relief function is defined, which defines the elevations and depressions--in other words, the relief structure of the surface--at each point of the surface element. The local normal vector for each point of the surface element is then calculated from the surface normal and the relief function through partial derivations. Because of the dependency of the reflection behavior on angle and direction, the brightness varies within the surface element as a function of the position of the local surface normals. Consequently, the relief structure of the surface can be simulated with consideration of the locally-alternating illumination and viewing directions and the resulting, different reflection behavior of the surface.
This method creates a relatively natural impression of the surface for all positions of the object. However,
REFERENCES:
patent: 5761401 (1998-06-01), Kobayashi et al.
IBM Technical Disc. Bulletin, Bd. 36, "Rendering of 3D Image Via Interpolated Z-buffer Gradient", Seiten 35-38, Sep. 1993.
Jackel et al. "A Real Time Rendering System With Normal Vector Shading" 9th EP Workshop on Graphics Hardware, Sep. 1994.
Heckbert et al., "Interpolation for Polygon Texture Mapping and Shading" State Of Art Computer Graphics: Visualization and Modelling, pp. 101-111, 1991.
Ernst Ines
Jackel Dietmar
Wittig Oliver
GMD - Forschungszentrum Informationstechnik GmbH
Kinberg Robert
Nguyen Phu K.
Spencer George H.
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