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Transcript of Ian Mallett (me), Cem Yuksel · PDF file Ian Mallett (me), Cem Yuksel University of Utah, USA....

  • Parameterization of Tabulated BRDFs Ian Mallett (me), Cem Yuksel

    University of Utah, USA

  • Background / Motivation

    ● BRDFs describe light scattering

    ● Extremely important to realism

    ● Measured data is realistic – e.g. Matusik et al. 2003

  • Background / Motivation

    BRDF Data Table BRDF

    Parameterization

    ● What parameterization (mapping of data to BRDF's angle space) should we use?

    θin

    φin

    θout

  • Background / Motivation

    ● Literature lacks general methods to compare and generate parameterizations!

  • Contributions

    1. Framework to generate and evaluate parameterizations

    2. Provide example parameterization and analysis

    3. Discuss related technical and theoretical issues

  • Mathematical Framework

    ● Want parameterization to importance-sample BRDF:

    γ is angle state vector (θin,φin,θout,φout) s is parameter vector (s inθ ,s inφ ,s outθ ,s outφ )

    ● We describe how to formulate this in the paper

    d γ d s

    ∝BRDF (γ)

    d γ d s

    ∝ BRDF (γ)

  • Example Parameterization

    ● Fit a quadratic Bézier curve for each table axis

    P1 P0

    P2

    Effect on BRDF data spacing: Higher density near specular plane (green/blue axes)

  • Example Parameterization

    0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

    1

    ch ro

    m e-

    st ee

    l tu

    ng st

    en -c

    ar bi

    de ss

    44 0

    st ee

    l ch

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    di an

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    in iu

    m br

    as s

    bl ue

    -m et

    al lic

    -p ai

    nt 2

    sp ec

    ul ar

    -b la

    ck -p

    he no

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    m at

    ite si

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    re d-

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    al lic

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    ld -m

    et al

    lic -p

    ai nt

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    gi ng

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    bl ac

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    -s te

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    09 da

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    35 sp

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    26 0

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    as tic

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    gr ay

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    iff us

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    al l

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    la st

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    r al

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    a- ox

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    sp ec

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    ph en

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    w hi

    te -m

    ar bl

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    flo n

    gr ee

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    te x

    ne op

    re ne

    -r ub

    be r

    ye llo

    w -p

    ai nt

    or an

    ge -p

    ai nt

    pi nk

    -f ab

    ric 2

    pi nk

    -fe lt

    ye llo

    w -p

    he no

    lic pi

    nk -p

    la st

    ic re

    d- fa

    br ic

    po ly

    et hy

    le ne

    w hi

    te -f

    ab ric

    2 pu

    re -r

    ub be

    r be

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    fa br

    ic w

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    -a cr

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    pi nk

    -fa br

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    hi te

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    ric

    Bezier Uniform Identity

  • Example Parameterization

    ● More examples in paper . . .

  • Higher-Order Reconstruction Filtering

    ● Important for measured data

    ● We suggest cubic B-spline – Good results

    – Efficient GPU implementation (Sigg and Hadwiger 2005)

  • Higher-Order Reconstruction Filtering

    Linear Filter Higher-Order Filter (Cubic B-spline)

  • Conclusion

    ● Propose new mathematical framework to generate and analyze parameterizations

    ● Validate our approach by generating and analyzing an example parameterization

    ● Discuss higher-order filtering for measured BRDFs

  • Questions

  • External Image Sources

    ● BRDF picture: Derived from https://en.wikipedia.org/wiki/Bidirectional_scattering _distribution_function#/media/File:BSDF05_800.png

    ● BRDF diagram: remade from http://cybertron.cg.tu-berlin.de/rapid_prototyping_1 1ws/rp_brdf/img/reflection_t.png

    ● University of Utah and CGI images adapted from respective websites

    http://cybertron.cg.tu-berlin.de/rapid_prototyping_11ws/rp_brdf/img/reflection_t.png http://cybertron.cg.tu-berlin.de/rapid_prototyping_11ws/rp_brdf/img/reflection_t.png

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