An Artist Friendly Hair Shading System Stefan Kinauer KAIST (Korea Advanced Institute of Science and Technology)
Jan 22, 2016
An Artist Friendly Hair Shading System
Stefan Kinauer
KAIST (Korea Advanced Institute of Science and Technology)
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Overview
● Physical based hair shading models
● Reformulation for better artist controllability
and
Application to a Single Scattering Model
● Results
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Shading of Hair
● Very complex in general
from [marschner03]
Kajiya and Kay’s model real hairresult of Marschner (03)
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Physical Based Models
● Single Scattering● Marschner et al. (2003)
●Longitudinal scattering functions M(θ)●Azimuthal scattering functions N(Φ)
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Physical Based Models
● final result
● primary highlight
● secondary highlight
● transmission component
● backscattering
● forward scattering
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Physical Based Models
● Single Scattering● Marschner et al. (2003)
● Multiple Scattering● Dual Scattering
by Zinke (08)
● Determined by a lot of Parameters● can be measured
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Controllability
● physical parameters are unintuitive● change of visual features affect other
featureschanging the refraction index influences other
optical features
increasing the width of the highlight depletes the brightness of the highlight
due to energy preservation
goal: decoupled behaviour
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Reformulation
● goal:● preserve the quality of hair shading● enable the artist to create non-physical
correct effects● provide controls for the artist to change
hair appearances●in exact the way the artist likes to●without influencing other features of the hair
● at least do not slow down the rendering process
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Reformulation
● Examination
● Decomposition
● Defining AFCs (Artist Friendly Controls)
● Reproduction
● Recombination
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ExaminationGeneral Approach applied to Marschner‘s
model
a unit-area Gaussian function
β: the longitudinal widthθh : the half angle between incoming and outgoing lightα: the longitudinal shift
with
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DecompositionGeneral Approach applied to Marschner‘s
model (artist-specifical)
● visual distinctive components to control
● primary highlight (R)
● secondary highlight (TRT)
● glints (TRT)
● rim light (TT)
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Defining Artist Friendly ControlsGeneral Approach applied to Marschner‘s
model (artist-specifical)
● the rim light:● color
● intensity
● azimuthal width
● longitudinal width
● longitudinal position
rim light
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ReproductionGeneral Approach applied to Marschner‘s
model
● longitudinal controls
● azimuthal controls
● combining
a unit-height Gaussian function
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RecombinationGeneral Approach applied to Marschner‘s
model
● summing up all terms
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What is missing here?
● Multiple Scattering Effects● basically the same steps● for details please have a look at the main
paper
● BUT: they areimportant!
[moon&marschner]
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Results
● In their tests it was significantly easier to produce wanted results
● The rendering is about 1.3 times faster than the corresponding physical shader
● Is currently used for Walt Disney Animation Studios
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Results
Walt Disney‘s Tangled
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Questions and Answers
● sources for this presentation:● [marschner03] Light Scattering from
Human Hair Fibers by Stephen R. Marschner et al.
● [moon&marschner] Simulating Multiple Scattering in Hair Using a Photon Mapping Approach by Jonathan T. Moon and Stephen R. Marschner
● The main paper: An Artist Friendly Hair Shading System by Iman Sadeghi, Heather Pritchett, Henrik Wann Jensen and Rasmus Tamstorf