Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1999-03-26
2001-11-20
Zimmerman, Mark (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
C345S423000, C345S442000, C345S581000, C345S589000
Reexamination Certificate
active
06320581
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to simulated illumination of planar, two-dimensional shapes, and in particular to generating an illusion of solidity associated with such shapes.
The invention has been developed primarily to provide individual tiles within a tessellated pattern with a simulated three-dimensional appearance, and shall be described hereinafter with reference to this application. However, it, will be appreciated that the invention is not limited to this field of use.
BACKGROUND OF THE INVENTION
There exists a number of standard illumination models for rendering three-dimensional graphical models with photorealistic results. Such models typically are composed of three-dimensional surfaces defined by geometrical primitives such as surface patches or meshes of polygonal facets. These models may also take into account a number of illuminating light sources.
The main illumination model used in three-dimensional computer graphics is based on the physical characteristics of incident rays of light illuminating a given scene or object. The model generates a variety of illumination components based upon the varying reflective properties of the surfaces being illuminated. These components include:
1. Ambient light, which illuminates all surfaces equally. The intensity of light reflected by a given primitive is dependent only upon the intensity of ambient light and the reflective coefficient of the surface. This results in relatively constant shading across the primitive.
2. Diffuse reflection, in which reflection across the surface varies according to the relationship between the angle to the light source and the surface normal at each point. Intensity increases as the two angles approach each other, and correspondingly decreases as the angles diverge, according to Lambert's Cosine Law. This results in smooth shading across the primitive that includes highlight and shadow regions. Gouraud shading produces this result.
3. Specular reflection, which is one or more sharply focussed highlight regions, typically exhibited by a “glossy” surface. Specular reflection is calculated from the relationship between the angle to the light source, the angle to the view point, and the surface normal. Phong shading produces this result.
The illumination of any point within a three-dimensional scene, relative to a view point, may be determined by adding the red, green and blue reflective contributions for each of the above reflective components, for each light source.
Unfortunately, to provide an accurate representation of a three-dimensional object, it is necessary to calculate intensity for the various colours and components on a per-pixel basis. This, and the accompanying three-dimensional geometry calculations, can place a relatively high load on a computer processor. This in turn limits the speed with which the appearance of a scene may be calculated. For the purposes of interaction, such as for games or multimedia applications, such speed restrictions are undesirable at best.
Accordingly, it is an object of the present invention to provide a method of applying various highlight and/or shadow components to a planar shape to suggest a three-dimensional interpretation thereof without requiring the complex, per-pixel intensity calculations of true three-dimension illumination modelling.
SUMMARY OF INVENTION
Accordingly, in a first aspect, the invention provides a method for simulating three-dimensional illumination of a planar shape element defined by a closed curve, the method including the steps of:
(a) providing a planar shape element having a colour Co;
(b) defining a colour Cw between Co and white;
(c) defining a maximum opacity Oh;
(d) generating a diffuse highlight element based on a first curve portion of the closed curve, the colour and opacity of the diffuse highlight element graduating from Cw,Oh at a first edge portion thereof to Co, 0 at a generally opposite second edge portion thereof;
(e) rendering the planar shape element and the diffuse highlight element for printing or display, such that the diffuse highlight element is layered on top of the planar shape element, thereby to simulate three-dimensional illumination thereof;
wherein steps (a) to (e) may be performed in any suitable order.
In a second aspect, the invention provides a method for simulating three-dimensional illumination of a planar shape element defined by a closed curve, the method including the steps of:
(a) providing a planar shape element having a colour Co;
(b) defining a colour Cb between Co and black;
(c) defining a maximum opacity Ol;
(d) generating a diffuse shadow element based on a first curve portion of the closed curve, the colour and opacity of the diffuse shadow element graduating from Cb,Ol at a first edge portion thereof to Co,0 at a generally opposite second edge portion thereof; and
(e) rendering the planar shape element and the diffuse shadow element for printing or display, such that the diffuse element is layered on top of the planar shape element, thereby to simulate three-dimensional illumination thereof;
wherein steps (a) to (e) may be performed in any suitable order.
In a third aspect, there is provided a method for simulating three-dimensional illumination of a planar shape element defined by a closed curve, the method including the steps of:
(a) providing a planar shape element having a colour Co;
(b) defining a colour Cw between Co and white;
(c) defining a colour Cb between Co and black;
(d) defining a maximum opacity Oh;
(e) defining a maximum opacity Ol;
(f) generating a diffuse highlight element based on a first curve portion of the closed curve, the colour and opacity of the diffuse highlight element graduating from Cw,Oh at a first edge portion thereof to Co, 0 at a generally opposite second edge portion thereof;
(g) generating a diffuse shadow element based on a second curve portion of the closed curve generally opposite the first curve thereof, the colour and opacity of the diffuse shadow element graduating from Cb,Ol at a first edge portion thereof to Co,0 at a generally opposite second edge portion thereof; and
(h) rendering the planar shape element, the diffuse highlight element and the diffuse shadow element for printing or display, such that the diffuse elements are layered on top of the planar shape element, thereby to simulate three-dimensional illumination thereof;
wherein steps (a) to (h) may be performed in any suitable order.
Preferably, the first edge portions of the diffuse highlight and shadow elements overlie the first and second curve portions of the closed curve upon which they are respectively based. It is also preferred that the respective second edge portions of the diffuse highlight and shadow elements are based on the first and second curve portions of the closed curve respectively. Desirably, the diffuse highlight and shadow elements are generated on the basis of preselected lighting parameters, which may include a light direction and a light elevation.
Preferably, the method further includes the steps of:
defining a plurality of normals extending outwardly from a corresponding plurality of points on the closed curve;
calculating an angle between the light direction and each of the plurality of outwardly extending normals;
using a section of the closed curve for which the calculated cosines are within a predetermined range, and for which the normals are generally opposed to the light direction, as the first curve portion; and
using a section of the closed curve for which the calculated cosines are within a predetermined range, and for which the normals are generally aligned with the light direction, as the second curve portion;
wherein the steps may be performed in any suitable order.
In a particularly preferred embodiment, the method further includes the steps of:
generating a specular element; and
during the rendering step, rendering the specular element such that it substantially overlaps the diffuse highlight element.
Throughout the specification, there appear a number of terms, which are defined as follows:
Cx—designates
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Kimbinh T.
Zimmerman Mark
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