Graphics image rendering with radiance self-transfer for low-frequency lighting environments

• US 20030179197A1
• Filed: 03/14/2003
• Published: 09/25/2003
• Est. Priority Date: 03/21/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Sloan, Peter-Pike J., Snyder, John M., Kautz, Jan
• Granted Patent: US 7,262,770 B2
• Time in Patent Office: Days
• US Class Current: 345/426
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

Real-time image rendering of diffuse and glossy objects in low-frequency lighting environments captures soft shadows, interreflections, and caustics. As a preprocess, a global transport simulator creates functions over the object'"'"'s surface representing transfer of arbitrary, low-frequency source lighting into exiting radiance, but including global effects like shadowing and interreflection from the object onto itself. At run-time, these transfer functions are applied to the actual source lighting. Dynamic, local lighting is handled by sampling close to the object at every frame; the object can also be rigidly rotated with respect to the lighting and vice versa. Lighting and transfer functions are represented using low-order spherical harmonics. Functions for radiance transfer from a dynamic lighting environment through a preprocessed object to neighboring points in space further allow cast soft shadows and caustics from rigidly moving casters onto arbitrary, dynamic receivers.

Claims

1. A method performed by a computer of rendering a computer graphics image of a geometrically modeled object, the method comprising:

simulating self-shadowing and inter-reflections for a plurality of locations on the modeled object to produce radiance transfer data representing the objects radiant response, including global transport effects, at the locations to a linear combination of area-supported lighting basis functions;

based on the radiance transfer data, evaluating radiance transfer at the locations of the modeled object in a lighting environment for a view direction; and

producing an image of the modeled object as shaded according to the radiance transfer evaluation.

2. The method of claim 1 wherein the simulating comprises simulating the modeled object as illuminated in a reference low frequency lighting environment.

3. The method of claim 1 wherein the radiance transfer data represents transfer of source radiance to exit radiance for the modeled object at the locations.

4. The method of claim 1 wherein the radiance transfer data represents transfer of source radiance to transferred incident radiance for the modeled object at the locations.

5. The method of claim 1 wherein the simulating lighting is performed as a pre-process and the evaluating and the producing is performed in real-time.

6. The method of claim 1 wherein the evaluating radiance transfer comprises:

calculating source lighting data for at least one sampling point in the lighting environment; and

performing a linear transformation on the calculated source lighting data according to pre-computed radiance transfer data for a plurality of locations on a surface of the modeled object to obtain data of exit radiance from the locations for a view, the radiance transfer data representing radiance response including global transport effects of the modeled object at the locations to source light under the reference lighting environment.

7. The method of claim 1 wherein the radiance transfer data comprises a radiance transfer vector representing radiance response for a location on a diffuse surface of the modeled object and wherein the evaluating radiance transfer comprises, for the diffuse surface of the modeled object:

calculating a source radiance vector for at least one sampling point in a lighting environment; and

calculating a dot-product of the source radiance vector and the radiance transfer vector.

8. The method of claim 1 wherein the radiance transfer data comprises data representing radiance response for a location on a glossy surface of the modeled object and wherein the evaluating radiance transfer comprises, for the glossy surface of the modeled object:

calculating a source radiance vector for at least one sampling point in a lighting environment;

determining exiting radiance for a viewing direction from the location as a function of the source radiance vector, the data representing radiance response for the location, and a bi-directional reflectance distribution function for the location.

9. The method of claim 1 wherein the radiance transfer data comprises data representing radiance response for a location on a glossy surface of the modeled object and wherein the evaluating radiance transfer comprises, for the glossy surface of the modeled object:

calculating a source radiance vector for at least one sampling point in a lighting environment;

determining transferred radiance for the location based on the source radiance vector and the data representing radiance response for the location; and

determining exiting radiance for a viewing direction from the location based on the transferred radiance and a bi-directional reflectance distribution function for the location.

10. The method of claim 1 wherein the radiance transfer data comprises a radiance transfer matrix representing radiance response for a location on a glossy surface of the modeled object and wherein the evaluating radiance transfer comprises, for the glossy surface of the modeled object:

calculating a source radiance vector for at least one sampling point in a lighting environment;

performing a matrix-vector multiplication of the source radiance vector and the radiance transfer matrix;

convolving a resulting product of the matrix-vector multiplication with a bi-directional reflectance distribution function for the location on the glossy surface of the modeled object; and

evaluating a result of the convolving for a viewing direction.

11. A method performed by a computer for real-time rendering of computer graphics images of a surface on a geometrically modeled object, the method comprising:

calculating source lighting data for at least one sampling point in a lighting environment;

performing a linear transformation on the calculated source lighting data according to pre-computed radiance transfer data for a plurality of locations on a surface of the modeled object to obtain data of exit radiance from the locations for a viewing direction, the radiance transfer data representing radiance response including global transport effects of the modeled object at the locations to source light under a reference lighting environment;

producing an image of the modeled object in the lighting environment for the viewing direction with shading according to the exit radiance from the locations.

12. The method of claim 11 wherein performing the linear transformation in case of a diffuse surface of the modeled object comprises calculating a dot-product of a source radiance vector and a pre-computed radiance transfer vector, the source radiance vector representing source light at a sampling point and the pre-computed radiance transfer vector representing radiance response for a location on the diffuse surface of the modeled object.

13. The method of claim 11 wherein performing the linear transformation in case of a glossy surface of the modeled object comprises:

calculating a source radiance vector for at least one sampling point in a lighting environment;

determining exiting radiance for a viewing direction from the location as a function of the source radiance vector, the data representing radiance response for the location, and a bi-directional reflectance distribution function for the location.

14. The method of claim 11 wherein performing the linear transformation in case of a glossy surface of the modeled object comprises:

calculating a source radiance vector for at least one sampling point in a lighting environment;

determining transferred radiance for the location based on the source radiance vector and the data representing radiance response for the location; and

determining exiting radiance for a viewing direction from the location based on the transferred radiance and a bi-directional reflectance distribution function for the location.

15. The method of claim 11 wherein performing the linear transformation in case of a glossy surface of the modeled object comprises:

performing a matrix-vector multiplication of a source radiance vector representing source light at a sampling point and a pre-computed radiance transfer matrix representing radiance response for a location on the glossy surface of the modeled object;

convolving a resulting product of the matrix-vector multiplication with a bi-directional reflectance distribution function for the location on the glossy surface of the modeled object; and

evaluating a result of the convolving for a viewing direction.

16. A method performed by a computer for real-time rendering of computer graphics images of a diffuse surface on a geometrically modeled object, the method comprising:

projecting radiance under a lighting environment to a spherical harmonic basis to produce a lighting coefficient vector for at least one location of the modeled object;

calculating a dot-product of the lighting coefficient vector with a pre-computed radiance transfer vector for at least one location on the diffuse surface to produce exit radiance at the at least one location on the diffuse surface of the modeled object for the lighting environment and view direction, the pre-computed radiance transfer vector representing radiance response including global transport effects of the diffuse surface. at the at least one location to source light under a reference low-frequency lighting environment;

calculating shading of the diffuse surface of the modeled object at the at least one location;

producing an image of the diffuse surface of the modeled object with the shading.

17. A method performed by a computer for real-time rendering of computer graphics images of a glossy surface on a geometrically modeled object, the method comprising:

projecting radiance under a lighting environment to a spherical harmonic basis to produce a lighting coefficient vector for at least one location of the modeled object;

determining exiting radiance for a viewing direction from at least one location on the glossy surface as a function of the lighting coefficient vector, a pre-computed radiance transfer matrix data representing radiance response including global transport effects of the glossy surface at the at least one location to source light under a reference low-frequency lighting environment, and a bi-directional reflectance distribution function for the at least one location;

calculating shading of the glossy surface of the modeled object at the at least one location;

producing an image of the glossy surface of the modeled object with the shading.

18. The method of claim 17 wherein determining exiting radiance for a viewing direction comprises:

performing a matrix-vector multiplication of the lighting coefficient vector with a pre-computed radiance transfer matrix for at least one location on the glossy surface, the pre-computed radiance transfer matrix representing radiance response including global transport effects of the glossy surface at the at least one location to source light under the reference low-frequency lighting environment;

convolving a resulting product of the matrix-vector multiplication with a bi-directional reflectance distribution function for the location on the glossy surface of the modeled object; and

evaluating a result of the convolving for a viewing direction.

19. The method of claim 17 wherein determining exiting radiance for a viewing direction comprises:

computing the exiting radiance based on a matrix-vector multiplication of the lighting coefficient vector with a pre-computed radiance transfer matrix for at least one location on the glossy surface, the pre-computed radiance transfer matrix representing radiance response including global transport effects of the glossy surface at the at least one location to source light under the reference low-frequency lighting environment.

20. A method performed by a computer of producing radiance self transfer data for use in real-time rendering and display of computer graphics images of a modeled object, the method comprising:

performing a global illumination simulation over the modeled object for a reference lighting environment represented as a linear combination of area-supported basis functions, the simulation calculating radiance transfer for a plurality of sample points on the modeled object, the simulation incorporating self-shadowing and inter-reflections of the modeled object; and

recording the global illumination simulation for the plurality of sample points as a linear transformation of the area-supported basis functions'"'"' coefficients for use in rendering radiance transfer over the modeled object to produce graphical images of the modeled object.

21. The method of claim 20 wherein the reference lighting environment is parameterized as a spherical harmonic basis projection of a sphere of incident light.

22. The method of claim 20 comprising:

performing the global illumination simulation in multiple passes over the modeled object;

in a first shadowing pass, simulating direct illumination of a plurality of sample points on the modeled object including self-shadowing of the modeled object, the direct illumination simulating comprising, for a sample point,

evaluating a plurality of directions from the sample point within a hemisphere about a normal direction to a surface of the modeled object at the sample point;

tagging those directions from the sample point that intersect the modeled object as being occluded;

accumulating radiance transfer from direct illumination of the sample point in the directions to produce radiance transfer data for the sample point; and

in subsequent interreflection passes, simulating interreflection illumination of the sample points on the modeled object, the interreflection illumination simulating comprising, for a sample point,

accumulating radiance transfer from interreflected illumination of the sample point in the directions tagged as occluded to produce radiance transfer data for the sample point;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

23. The method of claim 20 wherein the criteria is the total interreflection illumination energy of the current interreflection pass falls below a threshold level.

24. The method of claim 20 further comprising representing the radiance transfer data for a sample point on a diffuse surface of the modeled object as a vector of spherical harmonic basis coefficients.

25. The method of claim 20 further comprising representing the radiance transfer data for a sample point on a glossy surface of the modeled object as a matrix of spherical harmonic basis coefficients.

26. A method for real-time rendering of computer graphics images of a surface on a geometrically modeled object, the method comprising:

in a radiance transfer pre-computation phase performed on a first computer;

performing an illumination simulation of the modeled object in a reference low-frequency lighting environment to calculate radiance transfer for a plurality of sample points on the modeled object, the simulation incorporating self-shadowing and inter-reflections of the modeled object; and

in the case of a sample point on a diffuse surface of the modeled object, recording the calculated radiance transfer as a radiance transfer vector of spherical harmonic basis coefficients;

in the case of a sample point on a glossy surface of the modeled object, recording the calculated radiance transfer as a radiance transfer matrix of spherical harmonic coefficients;

in an image rendering phase performed on a second computer, rendering an image of the modeled object, said rendering comprising;

sampling source light for the modeled object in a rendering-time lighting environment to yield source radiance vectors in spherical harmonic basis coefficients for the sample points on the modeled object;

in the case of a sample point on a diffuse surface of the modeled object, performing a dot-product of the source radiance vector and the radiance transfer vector to yield exit radiance in a viewing direction;

in the case of a sample point on a glossy surface of the modeled object,

determining exit radiance for a viewing direction based on the source radiance vector, the radiance transfer matrix and a bi-directional reflectance distribution function for the glossy surface;

shading the modeled object at the sample points based on the exit radiance in the viewing direction for the respective sample points.

27. The method of claim 26 wherein determining exit radiance for the viewing direction comprises:

multiplying the source radiance vector and the radiance transfer matrix; and

evaluating a convolution of the product of the source radiance vector and the radiance transfer matrix with a bi-directional reflectance distribution function for the glossy surface at the sample point for the viewing direction to yield exit radiance in the viewing direction.

28. The method of claim 26 further comprising, in an image rendering phase performed on a second computer:

selecting the rendering-time lighting environment under user control; and

rendering further images of the modeled object for various user control-selected lighting environments.

29. The method of claim 26 further comprising, in an image rendering phase performed on a second computer:

varying the viewing direction under user control; and

rendering further images of the modeled object for various user-controlled viewing directions.

30. A computer graphics image rendering system comprising:

a memory for storing a geometric model of an object;

an illumination simulator for simulating lighting self-shadowing and inter-reflections for a plurality of locations on the modeled object to produce radiance transfer data representing the object'"'"'s radiant response, including global transport effects, at the locations to a linear combination of area-supporting lighting basis functions;

a real-time image rendering engine for evaluating radiance transfer at the locations of the modeled object in a lighting environment for a view based on the radiance transfer data, and for producing an image of the modeled object as shaded according to the radiance transfer evaluation; and

an image output device for presenting the image.

31. The computer graphics image rendering system of claim 30 wherein the radiance transfer data represents transfer of source radiance to exit radiance for the modeled object at the locations.

32. The method of claim 30 wherein the radiance transfer data represents transfer of source radiance to transferred source radiance for the modeled object at the locations.

33. A computer graphics image rendering system comprising:

a memory for storing a geometric model of an object;

an illumination simulator for calculating radiance response parameterized on a spherical harmonics basis at a plurality of points on a surface of the object to a reference low-frequency lighting environment and inclusive of self-shadowing and inter-reflections by the object;

a real-time image rendering engine for computing source radiance at the points parameterized on the spherical harmonics basis, and for processing a transformation combining the source radiance and radiance response to yield exit radiance from the points for a view, and for producing an image of the object with the object shaded at the points according to the points'"'"' respective exit radiance for the view; and

an image output device for presenting the image.

34. A real-time graphics rendering system, comprising:

a memory for storing a geometric model of an object and radiance response data for a plurality of points on a surface of the object as simulated in a reference lighting environment represented as a linear combination of area-supported basis functions and inclusive of self-shadowing and inter-reflection by the object;

a real-time image rendering engine for computing source radiance at the points, and for processing a transformation combining the source radiance and radiance response to yield exit radiance from the points for a view, and for producing an image of the object with the object shaded at the points according to the points'"'"' respective exit radiance for the view; and

an image output device for presenting the image.

35. The real-time graphics rendering system of claim 34 wherein the radiance response data is parameterized on a spherical harmonics basis.

36. The real-time graphics rendering system of claim 34 wherein the incident radiance is parameterized on a spherical harmonics basis.

37. A computer-readable data carrying medium having program code carried thereon for processing data comprising a geometric model of an object and radiance self-transfer response for a plurality of points on the object to thereby render images of a geometrically modeled object, the program code comprising:

program code means for computing source lighting at one or more sample points near the object in a lighting environment represented as a linear combination of area-supported basis functions; and

program code means for combining data of the source lighting with the radiance self-transfer response to yield exit radiance from the point on the object in a viewing direction.

38. The computer-readable data carrying medium of claim 37 wherein the radiance self-transfer response data comprises, for a point on a diffuse surface of the object, a radiance self-transfer response vector on an area-supported lighting basis, and the program code further comprises program code means for, in case of the point on the diffuse surface of the object, performing a dot-product of a source light vector with the radiance self-transfer response vector to yield the exit radiance from the point on the object in the viewing direction.

39. The computer-readable data carrying medium of claim 38 wherein the area-supported lighting basis is a spherical harmonic basis.

40. The computer-readable data carrying medium of claim 37 wherein the radiance self-transfer response data comprises, for a point on a glossy surface of the object, a radiance self-transfer response matrix on a spherical harmonics basis, and the program code further comprises program code means for, in case of the point on the glossy surface of the object, determining the exit radiance from the point on the object in a viewing direction based on a source light vector, the radiance self-transfer response matrix, and a bi-directional reflectance distribution function.

41. The computer-readable data carrying medium of claim 40 wherein determining the exit radiance comprises:

performing a matrix-vector multiplication of the source light vector with the radiance self-transfer response matrix;

42. The computer-readable data carrying medium of claim 41 wherein determining the exit radiance further comprises:

convolving the product of the matrix-vector multiplication with a bi-directional reflectance distribution function evaluated for the viewing direction to yield the exit radiance from the point on the object in the viewing direction.

43. The computer-readable data carrying medium of claim 37 wherein the radiance self-transfer response data comprises a radiance self-transfer response matrix, and the program code further comprises program code means for determining the exit radiance from a point on the object for a viewing direction by performing a matrix-vector multiplication of the source light vector with the radiance self-transfer response matrix.

44. A method performed by a computer of evaluating an incident radiance field in a low frequency lighting environment for use in rendering and display of computer graphics images of a modeled object in the lighting environment, the method comprising:

producing images of source radiance at a plurality of directions from a point in the lighting environment;

converting the images to a representation as a linear combination of area-supported lighting basis functions of the source radiance field at the point in the lighting environment;

using the lighting basis representation to shade the modeled object at the point in rendering an image of the modeled object in the lighting environment; and

visually presenting the image of the modeled object in the lighting environment.

45. The method of claim 44 wherein the lighting basis representation is a spherical harmonic basis representation.

46. A method using graphics hardware on a computer to capture radiance samples in a dynamic scene with a lighting environment for use in rendering and display of computer graphics images of a modeled object in the scene, the method comprising:

storing a set of precomputed texture images representing area-supported lighting basis functions;

on the graphics hardware, rendering a set of images from a sample point in the dynamic scene, the images representing source light from the lighting environment in the dynamic scene;

on the graphics hardware, projecting the source radiance at the sample point as a function of the set of source light images and the set of precomputed texture images to yield the source radiance at the sample point in the area-supported lighting basis;

using the source radiance at the sample point to shade the modeled object at the point in rendering an image of the modeled object in the lighting environment; and

visually presenting the image of the modeled object in the lighting environment.

47. The method of claim 46 wherein the precomputed texture images represent a set of spherical harmonics (SH) basis functions.

48. The method of claim 47 wherein the set of spherical harmonics basis functions are weighted by differential solid angle and evaluated over a cube map spherical parameterization of the angle.

49. The method of claim 46 wherein the rendered images correspond to faces of a cube map spherical parameterization of incident light from the low frequency lighting environment in the dynamic scene.

50. A method using graphics hardware on a computer to capture radiance samples in a dynamic scene with a lighting environment for use in rendering and display of computer graphics images of a modeled object in the scene, the method comprising:

storing a set of precomputed texture images for a set of spherical harmonics (SH) basis functions weighted by differential solid angle and evaluated over a cube map spherical parameterization of the angle;

on the graphics hardware, rendering a set of images from a sample point in the dynamic scene, the images corresponding to faces of a cube map spherical parameterization of source light from the lighting environment in the dynamic scene;

on the graphics hardware, projecting the source radiance at the sample point into spherical harmonics coefficients as a dot product of the set of source light images and the set of SH basis functions texture images to yield the source radiance at the sample point on the SH basis;

using the source radiance on the SH basis at the sample point to shade the modeled object at the point in rendering an image of the modeled object in the lighting environment; and

visually presenting the image of the modeled object in the lighting environment.

51. The method of claim 50 further comprising repeating the acts of rendering and projecting for a plurality of spatially disparate sample points in the dynamic scene.

52. The method of claim 50 further comprising, prior to projecting into SH coefficients, super-sampling and box-filter decimating the source light images, whereby aliasing is reduced.

53. The method of claim 50 further comprising, prior to projecting into SH coefficients, super-sampling and box-filter decimating the SH basis functions texture images.

54. A computer system for graphics rendering, comprising:

a memory for storing a set of precomputed texture images for a set of spherical harmonics (SH) basis functions weighted by differential solid angle and evaluated over a cube map spherical parameterization of the angle;

a graphics processing board operating to render a set of images from a sample point in a dynamic scene having a lighting environment, the images corresponding to faces of a cube map spherical parameterization of source light from the lighting environment in the dynamic scene, and further operating to project the source radiance at the sample point into spherical harmonics coefficients as a dot product of the set of source light images and the set of SH basis functions texture images to yield the source radiance at the sample point on the SH basis;

a system processor executing a real-time image rendering engine operating to use the source radiance on the SH basis at the sample point to shade the modeled object at the point in rendering an image of the modeled object in the lighting environment;

an image output device for presenting the image.

55. A computer-readable data carrying medium having program code carried thereon for using graphics hardware on a computer to capture radiance samples in a dynamic scene with a lighting environment for use in rendering and display of computer graphics images of a modeled object in the scene, the program code comprising:

program code means for causing the graphics hardware to render a set of images from a sample point in the dynamic scene, the images corresponding to faces of a cube map spherical parameterization of source light from the low frequency lighting environment in the dynamic scene;

program code means for causing the graphics hardware to project the source radiance at the sample point into spherical harmonics coefficients as a dot product of the set of source light images and a set of precomputed SH basis functions texture images for a set of spherical harmonics (SH) basis functions weighted by differential solid angle and evaluated over a cube map spherical parameterization of the angle to yield the source radiance at the sample point on the SH basis;

program code means for using the source radiance on the SH basis at the sample point to shade the modeled object at the point in rendering an image of the modeled object in the lighting environment; and

program code means for visually presenting the image of the modeled object in the lighting environment.

56. A method performed by a computer of producing radiance self transfer data for use in real-time rendering and display of computer graphics images of a volumetric model, the method comprising:

simulating lighting self-shadowing and inter-reflections over the volume as illuminated to produce radiance transfer data representing radiance response including global transport effects to a linear combination of area-supported lighting basis functions for a plurality of volume elements of the volumetric model;

based on the radiance transfer data, evaluating radiance transfer for the plurality of volume elements in a lighting environment for a view; and

producing an image of the volumetric model as shaded according to the radiance transfer evaluation.

57. A method performed by a computer of producing radiance self transfer data for use in real-time rendering and display of computer graphics images of a volumetric model, the method comprising:

performing a global illumination simulation over the volume for a reference lighting environment represented as a linear combination of area-supported basis functions, the simulation calculating radiance transfer for a plurality of volume elements of the volumetric model, the simulation incorporating self-shadowing and inter-reflections of the volumetric model; and

recording the global illumination simulation for the plurality of volume elements as a linear transformation of the basis functions'"'"' coefficients for use in rendering radiance transfer over the volumetric model to produce graphical images of the volumetric model.

58. The method of claim 57 wherein the reference lighting environment is parameterized as a spherical harmonic basis projection of a sphere of incident light.

59. The method of claim 57 comprising:

performing the global illumination simulation in multiple passes over the volumetric model;

in a first shadowing pass, simulating direct illumination of a plurality of volume elements of the volumetric model in the reference lighting environment including attenuation along a path through the volumetric model;

in subsequent interreflection passes, simulating interreflection illumination of the volume elements of the volumetric model by other volume elements of the volumetric model, including attenuation through the volumetric model;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

60. A method performed by a computer for real-time rendering of computer graphics images of a volumetric model, the method comprising:

calculating source lighting data for at least one sampling point in a lighting environment;

performing a linear transformation on the calculated source lighting data according to pre-computed radiance transfer data for a plurality of volume elements in the volumetric model to obtain data of exit radiance from the volume elements for a view, the radiance transfer data representing radiance response including global transport effects of the volumetric model at the locations to source light under a reference lighting environment;

producing an image of the modeled object in the lighting environment for the viewing direction with shading according to the exit radiance from the locations.

61. The method of claim 60 comprising:

as a pre-computation, performing a global illumination simulation over the volume for a reference lighting environment parameterized as a spherical harmonic basis projection of a sphere of incident light, the projection having spherical harmonic coefficients, the simulation calculating radiance transfer for a plurality of volume elements of the volumetric model, the simulation incorporating self-shadowing and inter-reflections of the volumetric model; and

recording the global illumination simulation for the plurality of volume elements as a linear transformation of the spherical harmonic coefficients of the source light to form the radiance transfer data.

62. The method of claim 61 comprising:

performing the global illumination simulation in multiple passes over the volumetric model;

in a first shadowing pass, simulating direct illumination of a plurality of volume elements of the volumetric model in the reference lighting environment including attenuation along a path through the volumetric model;

in subsequent interreflection passes, simulating interreflection illumination of the volume elements of the volumetric model by other volume elements of the volumetric model, including attenuation through the volumetric model;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

63. A computer graphics image rendering system for real-time rendering of computer graphics images of a volumetric model, the system comprising:

a memory for storing a volumetric model;

an illumination simulator for simulating lighting self-shadowing and inter-reflections for a plurality of volume elements of the volumetric model as illuminated in a reference lighting environment to produce data representing radiance transfer of source-to-exit light for the volume elements of the volumetric model;

a real-time image rendering engine for evaluating radiance transfer at the volume elements of the volumetric model in a second lighting environment for a view based on the radiance transfer data, and for producing an image of the volumetric model as shaded according to the radiance transfer evaluation; and

an image output device for presenting the image.

64. A computer-readable program-carrying media having a program carried thereon, the program being executable on a computer to perform a method of producing radiance self transfer data for use in real-time rendering and display of computer graphics images of a volumetric model, the method comprising:

performing a global illumination simulation over the volume for a reference low-frequency lighting environment parameterized as a spherical harmonic basis projection of a sphere of source light, the projection having spherical harmonic coefficients, the simulation calculating radiance transfer for a plurality of volume elements of the volumetric model, the simulation incorporating self-shadowing and inter-reflections of the volumetric model; and

recording the global illumination simulation for the plurality of volume elements as a linear transformation of the spherical harmonic coefficients of the source light for use in rendering radiance transfer over the volumetric model to produce graphical images of the volumetric model.

65. The media of claim 64 wherein the method further comprises:

performing the global illumination simulation in multiple passes over the volumetric model;

in a first shadowing pass, simulating direct illumination of a plurality of volume elements of the volumetric model in the reference low-frequency lighting environment including attenuation along a path through the volumetric model;

in subsequent interreflection passes, simulating interreflection illumination of the volume elements of the volumetric model by other volume elements of the volumetric model, including attenuation through the volumetric model;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

66. A computer-readable program-carrying media having a program carried thereon, the program being executable on a computer to perform a method for real-time rendering of computer graphics images of a volumetric model, the method comprising:

calculating source lighting data for at least one sampling point in a lighting environment;

performing a linear transformation on the calculated source lighting data according to pre-computed radiance transfer data for a plurality of volume elements in the volumetric model to obtain data of exit radiance from the volume elements for a view, the radiance transfer data representing radiance response including global transport effects to a linear combination of area-supported lighting basis functions of the volume elements in the volumetric model;

producing an image of the modeled object in the lighting environment for the view with shading according to the exit radiance from the locations.

67. The media of claim 66 wherein the method further comprises:

as a pre-computation, performing a global illumination simulation over the volume for a reference low-frequency lighting environment parameterized as a spherical harmonic basis projection of a sphere of source light, the projection having spherical harmonic coefficients, the simulation calculating radiance transfer for a plurality of volume elements of the volumetric model, the simulation incorporating self-shadowing and inter-reflections of the volumetric model; and

recording the global illumination simulation for the plurality of volume elements as a linear transformation of the spherical harmonic coefficients of the source light to form the radiance transfer data.

68. The media of claim 67 wherein the method further comprises:

performing the global illumination simulation in multiple passes over the volumetric model;

in a first shadowing pass, simulating direct illumination of a plurality of volume elements of the volumetric model in the reference low-frequency lighting environment including attenuation along a path through the volumetric model;

in subsequent interreflection passes, simulating interreflection illumination of the volume elements of the volumetric model by other volume elements of the volumetric model, including attenuation through the volumetric model;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

69. A method performed by a computer of producing radiance neighborhood transfer data from a modeled object in a scene for use in real-time rendering and display of computer graphics images of a modeled receiver in the scene, the method comprising:

performing a global illumination simulation over the modeled object for a reference lighting environment represented as a linear combination of basis functions, the simulation calculating radiance transfer for a plurality of sample points in a neighboring space about the modeled object, the simulation incorporating self-shadowing and inter-reflections cast from the modeled object on the sample points; and

recording the global illumination simulation for the plurality of sample points as a linear transformation of-the basis functions'"'"' coefficients for use in rendering radiance transfer over the volumetric model to produce graphical images of the volumetric model.

70. The method of claim 69 comprising:

performing the global illumination simulation in multiple passes over the modeled object;

in a first shadowing pass, simulating direct illumination of the sample points in the neighboring space about the modeled object in the reference low-frequency lighting environment including shadowing of the sample points from the modeled object;

in subsequent interreflection passes, simulating reflection illumination of the sample points in the neighboring space about the modeled object from the modeled object;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

71. The method of claim 69 wherein the recording the global illumination simulation for the plurality of sample points as a linear transformation of the spherical harmonic coefficients of the source light is in the form of a transfer matrix for a plurality of points in a 3 dimensional grid about the modeled object.

72. A method performed by a computer for real-time rendering of computer graphics images of a modeled receiver in a scene with a modeled object, the method comprising:

calculating source lighting data for at least one sampling point in a lighting environment;

performing a linear transformation on the calculated source lighting data according to pre-computed radiance neighborhood transfer data for a plurality of sample points in a neighboring space about the modeled object to obtain data of transferred radiance at locations on the modeled receiver for a view, the radiance transfer data representing radiance response including global transport effects of the modeled object at the sample points in the neighboring space about the modeled object to source light under a reference lighting environment;

producing an image of the modeled receiver in the lighting environment for the view with shading according to the transferred radiance from the locations.

73. The method of claim 72 wherein the act of performing the linear transformation comprises performing a dynamic rotation to align a coordinate system orientation of the sample points with that of the modeled receiver.

74. The method of claim 72 comprising:

as a pre-computation, performing a global illumination simulation of the modeled object for the reference lighting environment parameterized as a spherical harmonic basis projection of a sphere of source light, the projection having spherical harmonic coefficients, the simulation calculating radiance transfer for the plurality of sample points in the neighboring space about the modeled object, the simulation incorporating shadowing and reflections from the modeled object; and

recording the global illumination simulation for the plurality of sample points as a linear transformation of the spherical harmonic coefficients of the source light to form;

the radiance transfer data.

75. The method of claim 74 wherein the recording the global illumination simulation for the plurality of sample points as a linear transformation of the spherical harmonic coefficients of the source light is in the form of a transfer matrix for a plurality of points in a 3 dimensional grid about the modeled object.

76. The method of claim 74 comprising:

performing the global illumination simulation in multiple passes;

in a first shadowing pass, simulating direct illumination of the plurality of sample points in the neighboring space about the modeled object in the reference lighting environment including shadowing from the modeled object;

in subsequent reflection passes, simulating reflection illumination of the sample points by the modeled object;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

77. A computer graphics image rendering system for real-time rendering of computer graphics images of a modeled receiver in a scene with a modeled object, the system comprising:

a memory for storing models of the receiver and object;

an illumination simulator for simulating lighting self-shadowing and inter-reflections for a plurality of sample points in a neighboring space about the modeled object as illuminated in a reference lighting environment to produce data representing radiance transfer of source-to-transferred incident light for the sample points from the modeled object;

a real-time image rendering engine for evaluating radiance transfer at the sample points from the modeled object onto the modeled receiver in a second lighting environment for a view based on the radiance transfer data, and for producing an image of the modeled receiver as shaded according to the radiance transfer evaluation; and

an image output device for presenting the image.

78. A computer-readable program-carrying media having a program carried thereon for programming a computer to execute a method of producing radiance neighborhood transfer data from a modeled object in a scene for use in real-time rendering and display of computer graphics images of a modeled receiver in the scene, the method comprising:

performing a global illumination simulation over the modeled object for a reference lighting environment represented as a linear combination of basis functions, the simulation calculating radiance transfer for a plurality of sample points in a neighboring space about the modeled object, the simulation incorporating self-shadowing and inter-reflections cast from the modeled object on the sample points; and

recording the global illumination simulation for the plurality of sample points as a linear transformation of the basis functions'"'"' coefficients for use in rendering radiance transfer over the volumetric model to produce graphical images of the volumetric model.

79. The media of claim 78 wherein the method comprises:

performing the global illumination simulation in multiple passes over the modeled object;

in a first shadowing pass, simulating direct illumination of the sample points in the neighboring space about the modeled object in the reference lighting environment including shadowing of the sample points from the modeled object;

in subsequent interreflection passes, simulating reflection illumination of the sample points in the neighboring space about the modeled object from the modeled object;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.

80. The media of claim 79 wherein the recording the global illumination simulation for the plurality of sample points as a linear transformation is in the form of a transfer matrix for a plurality of points in a 3 dimensional grid about the modeled object.

81. A computer-readable program-carrying media having a program carried thereon for programming a computer to execute a method for real-time rendering of computer graphics images of a modeled receiver in a scene with a modeled object, the method comprising:

calculating source lighting data for at least one sampling point in a lighting environment;

performing a linear transformation on the calculated source lighting data according to pre-computed radiance neighborhood transfer data for a plurality of sample points in a neighboring space about the modeled object to obtain data of exit radiance at locations on the modeled receiver for a view, the radiance transfer data representing radiance response including global transport effects of the modeled object at the sample points in the neighboring space about the modeled object to source light under a reference lighting environment;

producing an image of the modeled receiver in the lighting environment for the viewing direction with shading according to the exit radiance from the locations.

82. The media of claim 81 wherein the act of performing the linear transformation comprises performing a dynamic rotation to align a coordinate system orientation of the sample points with that of the modeled receiver.

83. The media of claim 81 wherein the method comprises:

as a pre-computation, performing a global illumination simulation of the modeled object for the reference lighting environment parameterized as a spherical harmonic basis projection of a sphere of source light, the projection having spherical harmonic coefficients, the simulation calculating radiance transfer for the plurality of sample points in the neighboring space about the modeled object, the simulation incorporating shadowing and reflections from the modeled object; and

recording the global illumination simulation for the plurality of sample points as a linear transformation of the spherical harmonic coefficients of the source light to form the radiance transfer data.

84. The media of claim 83 wherein the recording the global illumination simulation for the plurality of sample points as a linear transformation of the spherical harmonic coefficients of the incident light is in the form of a transfer matrix for a plurality of points in a 3 dimensional grid about the modeled object.

85. The media of claim 83 wherein the method comprises:

performing the global illumination simulation in multiple passes;

in a first shadowing pass, simulating direct illumination of the plurality of sample points in the neighboring space about the modeled object in the reference lighting environment including shadowing from the modeled object;

in subsequent reflection passes, simulating reflection illumination of the sample points by the modeled object;

repeating interreflection passes until a criteria is met; and

summing for a sample point the radiance transfer data accumulated in the first shadowing pass and subsequent interreflection passes to produce total radiance transfer for the sample point.