1. An Artist Friendly Hair Shading System
Stefan Kinauer
KAIST (Korea Advanced Institute of Science and Technology) 1

2. Overview Physical based hair shading models
Reformulation for better artist controllability and Application to a Single Scattering Model
Results

3. Shading of Hair Very complex in general Kajiya and Kay’s model
real hair
result of Marschner (03)
+ multiple scattering effects
especially in bright hair there are translucent features
from [marschner03]

4. Physical Based Models Single Scattering Marschner et al. (2003)
Longitudinal scattering functions M(θ)
Azimuthal scattering functions N(Φ)

5. Physical Based Models final result primary highlight
secondary highlight
transmission component
backscattering
forward scattering
final result
primary highlight
secondary highlight
transmission component
backscattering
forward scattering

6. Physical Based Models Single Scattering Multiple Scattering
Marschner et al. (2003)
Multiple Scattering
Dual Scattering by Zinke (08)
Determined by a lot of Parameters
can be measured
there are a lot of other hair shading models

7. Controllability physical parameters are unintuitive
change of visual features affect other features
changing 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
top row: influences several features
middle row: energy preserving causes the highlight to go down
bottom row: increasing width of highlight doesn‘t influence the brightness of the highlight

8. 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

9. Reformulation Examination Decomposition
Defining AFCs (Artist Friendly Controls)
Reproduction
Recombination

10. a unit-area Gaussian function
Examination
General Approach
applied to Marschner‘s model
with
a unit-area Gaussian function
β: the longitudinal width
θh : the half angle between incoming and outgoing light
α: the longitudinal shift
and the NX functions in the normal plane to the hair fibre

11. Decomposition General Approach
applied to Marschner‘s model (artist-specifical)
visual distinctive components to control
primary highlight (R)
secondary highlight (TRT)
glints (TRT)
rim light (TT)

12. Defining Artist Friendly Controls
General Approach
applied to Marschner‘s model (artist-specifical)
the rim light:
color
intensity
azimuthal width
longitudinal width
longitudinal position
rim light

13. a unit-height Gaussian function
Reproduction
General Approach
applied to Marschner‘s model
longitudinal controls
azimuthal controls
combining
a unit-height Gaussian function

14. Recombination General Approach applied to Marschner‘s model
summing up all terms

15. What is missing here? Multiple Scattering Effects
basically the same steps
for details please have a look at the main paper
BUT: they are important!
if dual scattering relies on single scattering -> single scattering needs to be normalized for multiple scattering , otherwise either scattering vanishes or blurres up
[moon&marschner]

16. 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

17. Results Walt Disney‘s Tangled
pay attention to primary and secundary highlights
scattering effects
Walt Disney‘s Tangled

18. 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