Mid-field and far-field irradiance approximation

• US 7,952,582 B1
• Filed: 06/08/2007
• Issued: 05/31/2011
• Est. Priority Date: 06/09/2006
• Status: Active Grant

• Current Assignee: Pixar (The Walt Disney Company)
• Original Assignee: Pixar (The Walt Disney Company)
• Inventors: Arvo, Jim
• Primary Examiner(s): Nguyen; Kimbinh T
• Application Number:
  US11/760,532
• Time in Patent Office: 1,453 Days
• Field of Search: 345/419, 345/426, 345/473, 345/420, 345/427
• US Class Current: 345/426
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

A computerized method for computing an approximation for irradiance at a point in space from a plurality of distant lights sources includes determining a normal to a surface at a point on the surface being illuminated by the light sources, and determining a direction from the light sources to the point. The method further includes retrieving a function of the normal and the direction wherein the function is configured to provide an approximation of the irradiance, and combining the function with a function of distance, wherein the distance is from the light sources to the point. The method further includes determining an approximation for the irradiance at the point from the combined function with the function of distance based on the normal, the direction, and the distance.

Claims

1. A computerized method for computing an approximation for irradiance at a point in space from a plurality of distant lights sources comprising:

determining by a computer a normal to a surface at a point on the surface being illuminated by the light sources;

determining by the computer a direction from the light sources to the point;

retrieving by the computer from a non-transitory computer-readable memory a function of the normal and the direction wherein the function is configured to provide an approximation of the irradiance;

combining by the computer the function with a function of distance, wherein the distance is from the light sources to the point; and

determining by the computer an approximation for the irradiance at the point from the combined function with the function of distance based on the normal, the direction, and the distance.

2. The method of claim 1, wherein the determining step includes determining by the computer a direction from the center of the light sources to the point, and the distance is from the center to the point.

3. The method of claim 2, wherein the function is separable.

4. The method of claim 3, wherein each factor in the separation is a linear combination of basis functions.

5. The method of claim 2, wherein the function is a four-dimensional lookup table.

6. The method of claim 2, wherein the function is two two-dimensional lookup tables.

7. The method of claim 2, wherein the function is a linear combination of basis function.

8. The method of claim 7, wherein the basis functions are spherical wavelets.

9. The method of claim 8, wherein the spherical wavelets are four-dimensional wavelets.

10. The method of claim 8, wherein the basis functions are spherical harmonics.

11. The method of claim 2, wherein the function is a pre-computed function.

12. The method of claim 2, further comprising storing by the computer in the non-transitory computer-readable memory a value for the approximation for the irradiance for the point.

13. The method of claim 2, wherein the irradiance value represents a reflection of the light sources from the point.

14. The method of claim 2, further comprising repeating by the computer the steps of the method for a plurality of points on the surface to generate a reflection image of the light sources from the points.

15. The method of claim 14, further comprising storing by the computer in the non-transitory computer-readable memory values for the irradiance at the points.

16. The method of claim 15, wherein the values are configured for use to generate an image that is configured for use in a feature.

17. The method of claim 16, wherein the feature is an animated feature.

18. The method of claim 2, wherein the function of distance is an inverse function of the distance.

19. The method of claim 18, wherein the function is an inverse function of the distance squared.

33. The computer program product of claim 21, further comprising code for repeating the code steps of claim 2 for a plurality of points on the surface to generate a reflection image of the light sources from the points.

34. The computer program product of claim 33, further comprising code storing values for the irradiance at the points.

35. The computer program product of claim 34, wherein the values are configured for use to generate an image that is configured for use in a feature.

36. The computer program product of claim 35, wherein the feature is an animated feature.

52. The computer system of claim 40, further comprising code for repeating the code steps of claim 2 for a plurality of points on the surface to generate a reflection image of the light sources from the points.

53. The computer system of claim 52, further comprising code storing values for the irradiance at the points.

54. The computer system of claim 53, wherein the values are configured for use to generate an image that is configured for use in a feature.

55. The computer system of claim 54, wherein the feature is an animated feature.

20. A computer program product storable on a non-transitory memory for a computerized method for computing an approximation for irradiance at a point in space from a plurality of distant lights sources comprises:

code for determining a normal to a surface at a point on the surface being illuminated by the light sources;

code for determining a direction from the light sources to the point;

code for retrieving a function of the normal and the direction wherein the function is configured to provide an approximation of the irradiance;

code for combining the function with a function of distance, wherein the distance is from the light sources to the point; and

code for determining an approximation for the irradiance at the point from the combined function with the function of distance based on the normal, the direction, and the distance.

21. The computer program product of claim 20, wherein the code for the determining step includes code for determining a direction from the center of the light sources to the point, and the distance is from the center to the point.

22. The computer program product of claim 21, wherein the function is separable.

23. The computer program product of claim 22, wherein each factor in the separation is a linear combination of basis functions.

24. The computer program product of claim 21, wherein the function is a four-dimensional lookup table.

25. The computer program product of claim 21, wherein the function is two two-dimensional lookup tables.

26. The computer program product of claim 21, wherein the function is a linear combination of basis function.

27. The computer program product of claim 26, wherein the basis functions are spherical wavelets.

28. The computer program product of claim 27, wherein the spherical wavelets are four-dimensional wavelets.

29. The computer program product of claim 28, wherein the basis functions are spherical harmonics.

30. The computer program product of claim 21, wherein the function is a pre-computed function.

31. The computer program product of claim 21, further comprising code for storing a value for the approximation for the irradiance for the point.

32. The computer program product of claim 21, wherein the irradiance value represents a reflection of the light sources from the point.

37. The computer program product of claim 21, wherein the function of distance is an inverse function of the distance.

38. The computer program product of claim 37, wherein the function is an inverse function of the distance squared.

39. A computer system for running a computer program product for a computerized method for computing an approximation for irradiance at a point in space from a plurality of distant lights sources comprises:

a processor for executing computer code;

a memory for storing the computer code;

a bus system for transferring the computer code from the memory to the processor for processing,

wherein the computer code includes;

code for determining a normal to a surface at a point on the surface being illuminated by the light sources;

code for determining a direction from the light sources to the point;

code for retrieving a function of the normal and the direction wherein the function is configured to provide an approximation of the irradiance;

code for combining the function with a function of distance, wherein the distance is from the light sources to the point; and

code for determining an approximation for the irradiance at the point from the combined function with the function of distance based on the normal, the direction, and the distance.

40. The computer system of claim 39, wherein the code for the determining step includes code for determining a direction from the center of the light sources to the point, and the distance is from the center to the point.

41. The computer system of claim 40, wherein the function is separable.

42. The computer system of claim 41, wherein each factor in the separation is a linear combination of basis functions.

43. The computer system of claim 40, wherein the function is a four-dimensional lookup table.

44. The computer system of claim 40, wherein the function is two two-dimensional lookup tables.

45. The computer system of claim 40, wherein the function is a linear combination of basis function.

46. The computer system of claim 45, wherein the basis functions are spherical wavelets.

47. The computer system of claim 46, wherein the spherical wavelets are four-dimensional wavelets.

48. The computer system of claim 47, wherein the basis functions are spherical harmonics.

49. The computer system of claim 40, wherein the function is a pre-computed function.

50. The computer system of claim 40, further comprising code for storing a value for the approximation for the irradiance for the point.

51. The computer system of claim 40, wherein the irradiance value represents a reflection of the light sources from the point.

56. The computer system of claim 40, wherein the function of distance is an inverse function of the distance.

57. The computer system of claim 56, wherein the function is an inverse function of the distance squared.