Distributed Ray Tracing

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

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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

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Distributed Ray Tracing
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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

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DRT Gloss/Translucency

• Blurry reflections and refractions are produced
  by randomly perturbing the reflection and
  refraction rays from their "true" directions.

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Distributed Ray Tracing
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Reflection
4 rays
64 rays
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Transparency
4 rays
16 rays
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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

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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.

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CG Camera Models

• Pinhole ideal camera
• All rays go through single point
• Everything in focus -- unrealistic

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More Realistic Model

• Lenses with spherical surfaces
• Depth of field control

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DRT Depth of Field

• Each point in the scene appears as a circle on
  the image plane.

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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

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DRT Depth of field
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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
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Depth of Field
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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

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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

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Cook (1986)
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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

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Motion Blur
Post-process blurring can get some effects, but
consider

• Two objects moving so that one always obscures
  the other
• Cant render and blur objects separately
• A spinning top with texture blurred but
  highlights sharp
• Cant post-process blur a rendered object
• The blades of a fan creating a blurred shadow
• Must consider the movement of other objects time

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Temporal Jittering Sampling
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Motion Blur
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Cook (1986)
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Cook (1986)
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Distributed Ray Tracing (Summary)