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Distributed Ray Tracing

Apply distribution-based sampling to various aspects of the ray-tracing method for realistic rendering effects such as gloss, depth of field, soft shadows, and motion blur.

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Distributed Ray Tracing

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  1. Distributed Ray Tracing Robert L. Cook Thomas Porter Loren Carpenter Computer Division Lucasfilm Ltd. SIGGRAPH 1984

  2. Distributed Ray Tracing Cook-Porter-Carpenter (1984) Apply distribution-based sampling to many parts of the ray-tracing algorithm Rays can also be stochastically distributed in object space to simulate Gloss/Translucency • Perturb directions reflection/transmission, with distribution based on angle from ideal ray Depth of field • Perturb eye position on lens Soft shadow • Perturb illumination rays across area light Motion blur • Perturb eye ray samples in time

  3. Distributed Ray Tracing Apply distribution-based sampling to many parts of the ray-tracing algorithm Rays can also be stochastically distributed in object space to simulate Gloss • rays are distributed reflections around reflection direction to simulate non-smooth surfaces Depth of field • origin of rays is distributed with respect to lens to get out-of-focus effect Soft shadow • rays are distributed around light direction to simulate area light sources Motion blur • rays are distributed in time to simulate object movement

  4. Distributed Ray Tracing

  5. Distributed Ray Tracing Rays can also be stochastically distributed in object space to simulate Gloss • rays are distributed reflections around reflection direction to simulate non-smooth surfaces Depth of field • origin of rays is distributed with respect to lens to get out-of-focus effect Soft shadow • rays are distributed around light direction to simulate area light sources Motion blur • rays are distributed in time to simulate object movement

  6. DRT: Gloss/Translucency • Blurry reflections and refractions are produced by randomly perturbing the reflection and refraction rays from their "true" directions.

  7. Distributed Ray Tracing

  8. Reflection 4 rays 64 rays

  9. Transparency 4 rays 16 rays

  10. Distributed Ray Tracing Rays can also be stochastically distributed in object space to simulate Gloss • rays are distributed reflections around reflection direction to simulate non-smooth surfaces Depth of field • origin of rays is distributed with respect to lens to get out-of-focus effect Soft shadow • rays are distributed around light direction to simulate area light sources Motion blur • rays are distributed in time to simulate object movement

  11. Depth of Field • The area in front of your camera where everything looks sharp and in focus. • objects falling within that area will be acceptably-sharp and in focus; • objects falling outside the area will be soft and out of focus.

  12. CG Camera Models • Pinhole – ideal camera • All rays go through single point • Everything in focus -- unrealistic

  13. More Realistic Model • Lenses with spherical surfaces • Depth of field control

  14. DRT: Depth of Field • Each point in the scene appears as a circle on the image plane.

  15. DRT: Depth of field • The lens has a diameter of F/n .The lens is focused at a distance P so that the image plane is at a distance Vp • Points on the plane that is a distance D from the lens will focus at

  16. DRT: Depth of field

  17. DRT: Depth of field For a point I on the image plane, the rays we trace lie inside the cone whose radius at D is

  18. Depth of Field

  19. Distributed Ray Tracing Rays can also be stochastically distributed in object space to simulate Gloss • rays are distributed reflections around reflection direction to simulate non-smooth surfaces Depth-of-view • origin of rays is distributed with respect to lens to get out-of-focus effect Soft shadow • rays are distributed around light direction to simulate area light sources Motion blur • rays are distributed in time to simulate object movement

  20. Soft Shadows • Consider the light source to be an area, not a point • Trace rays to random areas on the surface of the light source distribute rays according to areas of varying intensity of light source (if any) • Use the fraction of the light intensity equal to the fraction of rays which indicate an unobscured light source

  21. Cook (1986)

  22. Distributed Ray Tracing Rays can also be stochastically distributed in object space to simulate Gloss • rays are distributed reflections around reflection direction to simulate non-smooth surfaces Depth-of-view • origin of rays is distributed with respect to lens to get out-of-focus effect Soft shadow • rays are distributed around light direction to simulate area light sources Motion blur • rays are distributed in time to simulate object movement

  23. Motion Blur Post-process blurring can get some effects, but consider: • Two objects moving so that one always obscures the other • Can’t render and blur objects separately • A spinning top with texture blurred but highlights sharp • Can’t post-process blur a rendered object • The blades of a fan creating a blurred shadow • Must consider the movement of other objects time

  24. Temporal Jittering Sampling

  25. Motion Blur

  26. Cook (1986)

  27. Cook (1986)

  28. Distributed Ray Tracing (Summary)

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