Pseudo area lights

Abstract

Computer animators have, till now, largely relegated themselves to using point light sources when simulating directional light sources in computer graphics and animation. The illumination achieved is computationally feasible but not totally realistic. While it is possible to use a finite light source of given size and shape to achieve a more realistic effect, the radiosity analysis required to calculate the illumination effect of such a light source is so cumbersome that it cannot be used for real-time computer animation. The described invention allows the animator to approximate the illumination effect of a finite light source by using a point source of varying location and intensity. Another embodiment of the invention allows the animator to realistically simulate ambient light by a similar method. The resulting illumination effects are comparable to those achieved with full radiosity analyses at much lower computational loads.

1. A method for illuminating surfaces in computer graphics comprising the steps of:
 constructing a plurality of finite light sources within a computer animated scene, each of the finite light sources having a finite size and a center;  
 constructing a plurality of surfaces within the scene, each surface consisting of a plurality of points; and  
 approximating an illumination effect of each of the finite light sources by the use of a single point light source of varying intensity and location, taking into account the the  finite size and center of each of the finite light sources.  
 
     
     
       2. The method of  claim 1  wherein a portion of each of the light sources illuminates each of the points. 
     
     
       3. The method of  claim 2  comprising the further step of approximately calculating a light intensity and a light vector direction as a function of the portion of each of the light sources which illuminates each of the points. 
     
     
       4. The method of  claim 3  comprising the further step of calculating the light intensity as a function of the portion of the light source which illuminates each of the points. 
     
     
       5. The method of  claim 4  comprising the further step of approximating the light vector direction as a function of the portion of the light source shines upon the point. 
     
     
       6. The method of  claim 1  wherein said finite light source is a sphere. 
     
     
       7. A method for illuminating surfaces in a computer-modeled scene comprising the steps of:
 constructing a plurality of hemispherical light source of finite radius;  
 constructing a plurality of surfaces with said scene, said surfaces consisting of a plurality of points; and  
 approximating an illumination effect of each of the hemispherical light source by the use of a plurality of point light sources.  
 
     
     
       8. The method of  claim 7 , comprising the further step of calculating a light intensity and a light vector direction as a function of a portion of the light source which illuminates each of the points. 
     
     
       9. The method of  claim 8  wherein said light vector direction is a function of the portion of said hemispherical light source which shines upon said point. 
     
     
       10. The method of  claim 9  wherein said light intensity is a function of the portion of said hemispherical light source which shines upon said point. 
     
     
       11. An apparatus for illuminating surfaces in computer graphics, the apparatus comprising:
   a memory configured to store information for a computer animated scene; and        a processor coupled to the memory, the processor configured to:      construct a plurality of finite light sources within the computer animated scene, each of the finite light sources having a finite size and a center;        construct a plurality of surfaces within the scene, each surface comprising a plurality of points; and        approximate an illumination effect of each of the finite light sources by the use of a single point light source of varying intensity and location, taking into account the finite size and center of each of the finite light sources.       
     
     
       12. The apparatus of  claim 11  wherein a portion of each of the light sources illuminates each of the points. 
     
     
       13. The apparatus of  claim 12  wherein, for each point, the processor is configured to approximately calculate a light intensity and a light vector direction as a function of the portion of each of the light sources which illuminates the point. 
     
     
       14. The apparatus of  claim 13  wherein, for each point, the processor is configured to calculate the light intensity as a function of the portion of the light source which illuminates the point. 
     
     
       15. The apparatus of  claim 14  wherein the processor is configured to approximate the light vector direction as a function of the portion of the light source that shines upon the point. 
     
     
       16. The apparatus of  claim 11  wherein at least one finite light source from the plurality of finite light sources is a sphere. 
     
     
       17. An apparatus for illuminating surfaces in a computer- modeled scene, the apparatus comprising:      a memory configured to store information for the scene; and        a processor coupled to the memory, the processor configured to:      construct a hemispherical light source;        construct a plurality of surfaces within said scene, said surfaces comprising a plurality of points; and        approximate an illumination effect of the hemispherical light source for each point in the plurality of points by use of a single point light source.       
     
     
       18. The apparatus of  claim 17  wherein the processor is configured to calculate a light intensity and a light vector direction for a point from a plurality of points as a function of a portion of the light source which illuminates the point. 
     
     
       19. The apparatus of  claim 18  wherein said light vector direction is a function of the portion of said hemispherical light source which shines upon said point. 
     
     
       20. The apparatus of  claim 19  wherein said light intensity is a function of the portion of said hemispherical light source which sines upon said point. 
     
     
       21. A method of determining an illumination effect of a finite light source using a computer system, the method comprising:
   providing a computer - animated scene comprising a finite light source having a position and a shape;        providing a surface within the computer - animated scene, the surface comprising a plurality of points; and        approximating, for each point in the plurality of points of the surface, an illumination effect of the finite light source for the point by using a point light source whose location and intensity is determined based upon a position of the point on the surface, the position of the finite light source, and the shape of the finite light source.     
     
     
       22. The method of  claim 21  wherein the approximating comprises determining the location and intensity of a point light source for a point based upon a portion of the finite light source that illuminates the point. 
     
     
       23. The method of  claim 21  wherein the shape of the finite light source is substantially a sphere. 
     
     
       24. A method of approximating an illumination effect of a finite light source using a computer system, the method comprising:
   providing a computer - animated scene comprising a finite light source having a position and a shape;        providing a surface within the computer - animated scene, the surface comprising a first point and a second point;        approximating the illumination effect of the finite light source for the first point by using a point light source whose location and intensity is determined based upon a position of the first point on the surface, the position of the finite light source, and the shape of the finite light source; and        approximating the illumination effect of the finite light source for the second point by using a point light source whose location and intensity is determined based upon a position of the second point on the surface, the position of the finite light source, and the shape of the finite light source;        wherein the location and intensity of the point light source determined for approximating the illumination effect for the second point are different from the location and intensity of the point light source determined for approximating the illumination effect for the first point.     
     
     
       25. The method of  claim 24  wherein:
   approximating the illumination effect for the first point comprises determining the location and intensity of the point light source based upon a portion of the finite light source that illuminates the first point; and        approximating the illumination effect for the second point comprises determining the location and intensity of the point light source based upon a portion of the finite light source that illuminates the second point.     
     
     
       26. A method of determining an illumination effect of a finite light source using a computer system, the method comprising:
   providing a computer - animated scene comprising a finite light source having a position and a shape;        providing a surface within the computer - animated scene, the surface comprising a plurality of points; and        approximating, for each point in the plurality of points, an illumination effect of the finite light source for the point by using a point light source whose location and intensity is determined based upon a portion of the finite light source that illuminates the point.     
     
     
       27. A method of illuminating surfaces in a computer- modeled scene, the method comprising:      providing ambient light in the scene, the ambient light provided by a lighted sphere;        providing one or more surfaces in the scene, the one or more surfaces comprising a plurality of points; and        approximating an illumination effect of the ambient light for each point in the plurality of points using a point light source, wherein the location and intensity of the point light source used for a point are determined based upon a portion of the lighted sphere illuminating the point.     
     
     
       28. The method of  claim 27  wherein the ambient light is skylight. 
     
     
       29. An apparatus for determining an illumination effect of a finite light source, the apparatus comprising:
   a memory configured to store a computer - animated scene comprising a finite light source having a position and a shape, the scene comprising a surface comprising a plurality of points; and        a processor coupled to the memory, the processor configured to approximate, for each point in the plurality of points, an illumination effect of the finite light source for the point by using a point light source whose location and intensity is determined based upon a position of the point on the surface, the position of the finite light source, and the shape of the finite light source.     
     
     
       30. An apparatus for illuminating surfaces in a computer- modeled scene, the apparatus comprising:      a memory configured to store information for the computer - modeled scene, the scene comprising an ambient light provided by a lighted sphere and a plurality of surfaces comprising a plurality of points; and        a processor coupled to the memory, the processor configured to approximate an illumination effect of the ambient light on the surfaces by approximating an illumination effect of the ambient light for each point in the plurality of points using a point light source, wherein the location and intensity of the point light source used for a point are determined based upon a portion of the lighted sphere illuminating the point.