photorealistic rendering. ray tracing v. photorealistic rendering what illumination effects are not...
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Photorealistic Rendering
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Photorealistic Rendering
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Ray tracing v. photorealistic rendering
What illumination effects are not captured by ray tracing?
What illumination effects are captured by ray tracing?
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AmbientLight
Ray tracing v. Photorealistic rendering
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Caustics
Ray tracing v. photorealistic rendering
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Color bleeding
Ray tracing v. photorealistic rendering
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Ray tracing v. photorealistic rendering
LDSE notation
L - LightD - DiffuseS - SpecularE - eye
LDELSEL[D|S]ELD+ELS*DEL[D|S]+E
Describe path 1/2/3 with path notation
Which is handled by ray tracing?
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Rendering samples the environment
How can the shading / illumination be modeled mathematically?
To understand how different graphics sampling strategies affect accuracy (or don’t)
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Shading as integration
Bidirectional Reflectance Distribution Function (BRDF)
Rendering Equation (also called the Transport Equation)
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Bidirectional Reflectance Distribution Function (BRDF)
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Light at a point incoming from all directions
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incoming - Field Radiance
Radiance - light at a point in a given direction
outgoing - Radiance exitance or surface radiance
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Integration estimation by sampling
Shading ‘equation’ not analytic
Need to estimate shading integral by sampling
Need to understand how best to control error
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Basic statistics
Probability density function (pdf)
Continuous random variable
Relative likelihood for the value of a continuous variable to occur at a point
Probability of a continuous random variable falling within a set is the integral of the pdf over the set
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Basic statistics
Expected value
Standard deviation
Variation
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Integration estimation by sampling
Monte Carlo Integration
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Average score by integration
p(x) - pdf of score at a point on target
f(x) - score at a point on target
if xi generated with p(x)
(dart throwing example)
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Integration estimation by sampling
How accurate is it?
How to estimate and reduce the error?
How to minimize the number of samples?
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Law of large numbers
In the limit, sampling is correct
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Stratified sampling
Sum of variances – break down into subproblems and get better estimate
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Law of diminishing returns
need 4x samples to get 2x better estimate
error related to standard deviation
standard deviation proportional to
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Non-uniform sampling distribution
Areas of high variability
Take more samples in those areas to reduce error
Give more weight to samples in sparse areas (value reflects more area)
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Importance sampling
sample non-uniform distribution
uniform sample & weigh by distribution
non-uniform sample & weigh evenly
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Alternatives to Ray Tracing
Trace rays from light source?
Trace more rays from eye?
Do both?
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Radiosity - Jim Kajiya
Propogate diffuse light around environment: LD*E
Break environment up into micro-patches
Not a ray tracing approach - usually combined with it
Determine pairwise visibility between each pair of micro-patches
From Heat Transfer Theory develped in the ‘50s
Precompute diffuse (viewer independent) illumination
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Radiosity - Form Factor
pairwise visibility of micropatches
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Radiosity - form factor
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Radiosity - form factor
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Radiosity
Solve large matrix equation
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Radiosity - progressive refinement
Initially
Itertively add emissions propogated around enviroment
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Radiosity
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Radiosity
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Path Tracing - Jim Kajiya
Extension of ray tracing
At every intersection, select random direction to generate secondary (and beyond) ray - Do this a lot
Until it hits a light sourceUntil a certain maximum depth
http://graphics.ucsd.edu/~iman/BDPT/Diagrams from:
Probabilistically terminate“Russian Roulette”
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Path Tracing
Improve by illuminating each intermediate point
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Path Tracing
Accurate - if enough rays are generated
Inefficient
Unbiased
Accurate in the limit
http://feeblemind.tuxfamily.org/dotclear/images/cimetiere-des-pixels/sunflow/sponza/sponza_SF-path_tracing-logo.png
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Path Tracing
http://graphics.ucsd.edu/~iman/BDPT/From:
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Path Tracing
http://sunflow.sourceforge.net/gallery/v0060/livingroom.png
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Light Tracing - Philip Dutre
Generate a bunch of ‘particles’ at light source
Trace each particle through environment
Every time a hitcalculate contribution to eyerandomly bounce particle into scene
Probabilistically terminate
unbiased
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Light Tracing
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Light Tracing
: www.graphics.cornell.edu/~eric/thesis/images.html
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Light Tracing
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Photon Mapping - Henrik Wann Jensen
2nd pass - ray tracing with indirect illumination coming from querying the photon map by shooting secondary rays
Biased - photon map is sparse, so at query point photon map is interpolated from close-by photon deposits
2 pass algorithm
1st pass - photons shot from light source and ‘deposited’ on surfaces as they bounce around the environment - probabalistically
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Photon Mapping
http://web.cs.wpi.edu/~emmanuel/courses/cs563/write_ups/zackw/photon_mapping/PhotonMapping.html
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Photon Map
http://jgt.akpeters.com/papers/Christensen99/Fig2a.jpg
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Photon Mapping
From
http://www.ypoart.com/tutorials/photon/index.php
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Photon Mapping
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Photon Mapping
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Bi-Directional Path Tracing
Generate paths from light
Generate paths from eye
Hook up vertices from one path to vertices of other path, to get multiple paths from eye to light
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Bi-Directional Path Tracing
http://graphics.ucsd.edu/~iman/BDPT/
From:
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Bi-Directional Path Tracing
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Bi-Directional Path Tracing
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Bi-Directional Path Tracing
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Consider
http://www.yafaray.org/documentation/userguide/lightingmethods#methods