Filtered specular reflection of linear light sources

• US 7,872,649 B1
• Filed: 06/08/2007
• Issued: 01/18/2011
• 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, PHU K
• Application Number:
  US11/760,504
• Time in Patent Office: 1,320 Days
• Field of Search: 345/426, 345/473, 345/474, 345/475, 356/133, 359/622, 703/2
• US Class Current: 345/426
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

An image rendering method for a computer system includes identifying a point in space to be illuminated from at least one line light for the point, and determining an illumination direction of the line light. The method further includes generating a plane passing through the point, and projecting the line light onto the plane. The method further includes determining a brightness contribution for the point responsive to a function characterizing the brightness contribution.

Claims

1. A computerized image rendering method for a computer system comprises:

identifying by the computer system a point in space to be illuminated from at least one line light for the point;

determining by the computer system an illumination direction of the line light;

generating by the computer system a plane passing through the point;

projecting by the computer system the line light onto the plane; and

determining by the computer system a brightness contribution for the point responsive to a function characterizing the brightness contribution.

2. The method of claim 1, wherein the step of projecting by the computer system includes projecting by the computer system the line light onto the plane based on the illumination direction.

3. The method of claim 2, wherein the function is pre-calculated.

4. The method of claim 2, wherein the illumination direction is based on a scattering function for the point.

5. The method of claim 2, wherein the orientation of the plane is based on the illumination direction.

6. The method of claim 2, wherein the function is a lookup table.

9. The method of claim 2, wherein the step of determining by the computer system the illumination direction includes determining by the computer system the reflection of a ray from the point to an observation point based on an observation angle of a viewer relative to the point.

10. The method of claim 9 further comprises generating by the computer system a cone from the point toward the line light, wherein a primary axis of the cone is the illumination direction and the point is the apex of the cone.

11. The method of claim 10, wherein the plane is perpendicular to the axis of the cone.

12. The method of claim 11 further comprises clipping by the computer system the projection of the line light against a circle as viewed through the cone from the point.

13. The method of claim 12, wherein the function is a lookup table, and the step of determining by the computer system the brightness contribution includes determining by the computer system the brightness contribution of the clipped two-dimensional projection via a parameterized look up in the lookup table.

14. The method of claim 13, wherein the at least one line light is a member of a plurality of line lights, and the method steps are repeated for each line light of the plurality.

15. The method of claim 14 further comprises determining by the computer system a subset of the plurality of line lights that intersect the cone via a hierarchy of bounding spheres technique.

16. The method of claim 2 further comprises storing by the computer system an image for a fuzzy-specular reflection from the line light on the point responsive to the brightness contribution.

17. The method of claim 2 further comprises:

repeating by the computer system the method steps for a plurality of points on a surface; and

storing in a computer memory by the computer system an image for a fuzzy-specular reflection from the line light on the point responsive to the brightness contribution.

7. The method of clam 6, wherein the lookup table is parameterized for identifying the line light and the brightness contributions and is associated with at least one filter function that is configured to spread the brightness of a reflection at the point to generate a fuzzy-specular reflection.

8. The method of claim 7 further comprises retrieving by the computer system the lookup table from computer memory.

18. A computer non-transitory medium storing a computer program executable by a computer system for image rendering wherein the computer program comprises:

code for identifying a point in space to be illuminated from at least one line light for the point;

code for determining an illumination direction of the line light;

code for generating a plane passing through the point;

code for projecting the line light onto the plane; and

code for determining a brightness contribution for the point responsive to a function characterizing the brightness contribution.

19. The non-transitory medium of claim 18, wherein the code for projecting includes code for projecting the line light onto the plane based on to the illumination direction.

20. The non-transitory medium of claim 19, wherein the function is pre-calculated.

21. The non-transitory medium of claim 19, wherein the illumination direction is based on a scattering function for the point.

22. The non-transitory medium of claim 19, wherein the orientation of the plane is based on the illumination direction.

23. The non-transitory medium of claim 19, wherein the function is a lookup table.

26. The non-transitory medium of claim 19, wherein the code for determining the illumination direction includes code for determining the reflection of a ray from the point to an observation point based on an observation angle of a viewer relative to the point.

27. The non-transitory medium of claim 26 further comprises code for generating a cone from the point toward the line light, wherein a primary axis of the cone is the illumination direction and the point is the apex of the cone.

28. The non-transitory medium of claim 27, wherein the plane is perpendicular to the axis of the cone.

29. The non-transitory medium of claim 27 further comprises code for clipping the projection of the line light against a circle as viewed through the cone from the point.

30. The non-transitory medium of claim 29, wherein the function is a lookup table, and the code for of determining the brightness contribution includes code for determining the brightness contribution of the clipped two-dimensional projection via a parameterized look up in the lookup table.

24. The non-transitory medium of clam 23, wherein the lookup table is parameterized for identifying the line light and the brightness contributions and is associated with at least one filter function that is configured to spread the brightness of a reflection at the point to generate a fuzzy-specular reflection.

25. The non-transitory medium of claim 24 further comprises code for retrieving the lookup table from memory.

31. A computer system for image rendering 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 identifying a point in space to be illuminated from at least one line light for the point;

code for determining an illumination direction of the line light;

code for generating a plane passing through the point;

code for projecting the line light onto the plane; and

code for determining a brightness contribution for the point responsive to a function characterizing the brightness contribution.

32. The computer system of claim 31, wherein the code for projecting includes code for projecting the line light onto the plane based on to the illumination direction.

33. The computer system of claim 32, wherein the function is pre-calculated.

34. The computer system of claim 32, wherein the illumination direction is based on a scattering function for the point.

35. The computer system of claim 32, wherein the orientation of the plane is based on the illumination direction.

36. The computer system of claim 32, wherein the function is a lookup table.

37. The computer system of clam 36, wherein the lookup table is parameterized for identifying the line light and the brightness contributions and is associated with at least one filter function that is configured to spread the brightness of a reflection at the point to generate a fuzzy-specular reflection.

38. The computer system of claim 37, wherein the code further comprises code for retrieving the lookup table from memory.

39. The computer system of claim 38, wherein the code further comprises code for determining the illumination direction includes code for determining the reflection of a ray from the point to an observation point based on an observation angle of a viewer relative to the point.

40. The computer system of claim 39, wherein the code further comprises code for generating a cone from the point toward the line light, wherein a primary axis of the cone is the illumination direction and the point is the apex of the cone.

41. The computer system of claim 40, wherein the plane is perpendicular to the axis of the cone.

42. The computer system of claim 41, wherein the code further comprises code for clipping the projection of the line light against a circle as viewed through the cone from the point.

43. The computer system of claim 41, wherein the function is a lookup table, and the code for of determining the brightness contribution includes code for determining the brightness contribution of the clipped two-dimensional projection via a parameterized look up in the lookup table.

44. A computer method of generating a computer lookup table, which includes brightness contributions to a reflection of a set of line lights from a surface, the method comprising for each line light:

determining by a computer a pair of coordinates to uniquely specify the line light in the table including;

determining by the computer a first coordinate that is a distance from a center of a unit circle surrounding the line light to a chord of the circle on which the line light lies, and

determining by the computer a second coordinate that is a fraction of the chord covered by the line light;

numerically integrating by the computer the brightness contribution along the line light with a filter function, which is configured to spread the light from the line light for generating a fuzzy-specular reflection of the line light on the surface;

storing by the computer in a computer memory in the table the brightness contribution of the line light at a location in the table associated with the pair of coordinates for line light; and

storing the table on a computer readable medium.

45. The computer method of claim 44, wherein the filter function is a symmetric function.

46. The computer method of claim 45, wherein the filter function is a Gaussian or a polynomial.

47. The computer method of claim 46, wherein the numerical integration step includes applying by the computer Simpson'"'"'s rule to the line light.