Interactive Relighting with Dynamic Reflectance

• US 20080309667A1
• Filed: 06/15/2007
• Published: 12/18/2008
• Est. Priority Date: 06/15/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Zhou, Kun, Lin, Stephen S., Chen, Yanyun, Guo, Baining
• Granted Patent: US 7,884,820 B2
• Time in Patent Office: Days
• US Class Current: 345/426
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

Interactive relighting with dynamic reflectance involves relighting a graphical scene with dynamic changes to the reflectance(s) in the graphical scene. A graphical scene may include source radiance, regions having reflectances, a surface spot, incident radiation from the source radiance at the surface sport, an incident direction, a viewing direction, exit radiance, and so forth. In an example embodiment, a graphical scene is relighted based on at least one adjusted reflectance of the graphical scene using an incident radiance at a surface spot that is separated into respective incident radiance components corresponding to different respective numbers of interreflections in the graphical scene. In another example embodiment, a graphical scene is relighted based on at least one adjusted reflectance of the graphical scene using a tensor representation for a reflectance of a surface spot with the tensor representation being segmented into three adjustable factors for lighting, viewing, and reflectance.

Claims

1. A method comprising:

lighting a graphical scene based on a source radiance, one or more scene reflectances, and a view direction, the graphical scene including a surface spot having a reflectance;

adjusting at least one reflectance of the graphical scene;

relighting the graphical scene based on the at least one adjusted reflectance of the graphical scene using an incident radiance at the surface spot that is separated into respective incident radiance components corresponding to different respective numbers of interreflections in the graphical scene; and

displaying the relighted graphical scene having the at least one adjusted reflectance.

2. The method as recited in claim 1, wherein the respective incident radiance components comprise three incident radiance components corresponding to direct incident radiance, one-interreflection incident radiance, and two-interreflection incident radiance.

3. The method as recited in claim 2, wherein the act of relighting comprises:

modeling the direct incident radiance in terms of wavelets;

modeling the one-interreflection incident radiance by fourth-order spherical harmonics; and

modeling the two-interreflection incident radiance as a scalar.

4. The method as recited in claim 1, wherein the act of relighting comprises:

using precomputed transfer tensors (PTTs) to relate the incident radiance components along each path to (i) the source radiance and (ii) reflectance functions of the one or more scene reflectances.

5. The method as recited in claim 1, wherein each incident radiance component represents incident radiance with respect to a sequence of bidirectional reflectance distribution function (BRDF) basis functions for surfaces along a light path from the source radiance to the surface spot.

6. The method as recited in claim 1, wherein the act of relighting comprises:

bifurcating specular reflections of the graphical scene into mirror parts and remainder parts; and

processing the mirror parts separately from the remainder parts.

7. A method comprising:

lighting a graphical scene based on a source radiance, one or more scene reflectances, and a view direction, the graphical scene including a surface spot having a reflectance;

adjusting at least one reflectance of the graphical scene;

relighting the graphical scene based on the at least one adjusted reflectance of the graphical scene using a tensor representation for the reflectance of the surface spot that is segmented into three adjustable factors comprising a lighting factor, a viewing factor, and a reflectance factor; and

displaying the relighted graphical scene having the at least one adjusted reflectance.

8. The method as recited in claim 7, wherein the act of relighting comprises:

approximating the tensor representation of the reflectance of the surface spot using a third-order tensor and a tensor factorization algorithm.

9. The method as recited in claim 7, wherein the act of relighting comprises:

extracting a mirror part from at least one reflectance function;

evaluating visual effects for the graphical scene that are derived from the mirror part; and

computing the tensor representation independent of the extracted mirror part.

10. The method as recited in claim 7, wherein the lighting factor reflects an incident direction for the source radiance with respect to the surface spot, the viewing factor reflects a view direction with respect to the surface spot, and the reflectance factor reflects an index into a reflectance function for the reflectance of the surface spot.

11. The method as recited in claim 7, wherein the lighting factor comprises a lighting matrix based on a sampling resolution of an incident direction, the viewing factor comprises a viewing matrix based on a sampling resolution of a view direction, and the reflectance factor comprises a reflectance matrix based on a sampling resolution of a reflectance index.

12. A method comprising:

lighting a graphical scene based on a source radiance, one or more scene reflectances, and a view direction, the graphical scene including a surface spot having a reflectance;

adjusting at least one reflectance of the graphical scene;

relighting the graphical scene based on the at least one adjusted reflectance of the graphical scene (i) using an incident radiance at the surface spot that is separated into respective incident radiance components corresponding to different respective numbers of interreflections in the graphical scene and (ii) using a tensor representation for the reflectance of the surface spot that is segmented into three adjustable factors comprising a lighting factor, a viewing factor, and a reflectance factor; and

displaying the relighted graphical scene having the at least one adjusted reflectance.

13. The method as recited in claim 12, wherein the act of displaying the relighted graphical scene comprises displaying the relighted graphical scene on a display screen;

and wherein the method further comprises;

prior to the act of displaying the relighted graphical scene, displaying the lighted graphical scene on the display screen.

14. The method as recited in claim 12, wherein the act of relighting is performed in real-time.

15. The method as recited in claim 12, wherein the one or more scene reflectances comprise bidirectional reflectance distribution functions (BRDFs) that are generated from at least one of measurements of real materials or a given reflectance model.

16. The method as recited in claim 12, wherein the act of relighting comprises:

extracting a high-frequency mirror part of specular reflection from a reflectance function; and

processing the high-frequency mirror part using precomputed visibility.

17. The method as recited in claim 12, wherein the act of adjusting comprises adjusting any of the one or more scene reflectances, including the reflectance of the surface spot.

18. The method as recited in claim 12, wherein the incident radiance components comprise a direct incident radiance component;

and wherein the act of relighting comprises;

determining the direct incident radiance component responsive to one or more portions of the source radiance that are visible at the surface spot.

19. The method as recited in claim 12, wherein the incident radiance components comprise a one-bounce interreflection incident radiance component;

and wherein the act of relighting comprises;

determining the one-bounce interreflection incident radiance component by performing acts comprising;

computing inner products between a one-bounce precomputed transfer tensor and reflectance function coefficients of each region of the graphical scene;

adding the computed inner products together to obtain one-bounce incident radiance; and

calculating an inner product between the one-bounce incident radiance and a matrix based on the lighting factor.

20. The method as recited in claim 12, wherein the incident radiance components comprise a two-bounce interreflection incident radiance component;

and wherein the act of relighting comprises;

determining the two-bounce interreflection incident radiance component by processing the source radiance as transferred through ordered pairs of regions of the graphical scene using a five-dimensional two-bounce precomputed transfer tensor and reflectance function coefficients for each of the ordered pairs of regions.