Graphics Reference
In-Depth Information
Hery figured out a way to do this, and the implemented shader has been used in
production since the film
The Spiderwick Chronicles
.
Regarding future work, Hery notes that it would be desirable to enable the
dynamic control of the realism adaptively. As mentioned above, ILM improved
the efficiency of the subsurface scattering shader by employing Jensen and Buh-
ler's “fast translucency” method. However, movie production involves animation:
the scene objects move between frames. It is problematic that the parts of the
scene where realism is desired often changes according to the animation of the
objects and the camera position. Precomputation, such as that employed in the
fast translucency algorithm, may become useless within a few frames. What is
needed is a way to adaptively improve efficiency based on the factors that affect
the final visual quality the most. The solution to this problem will likely need
ideas from both practitioners and academic researchers.
Hery also mentions that even when subsurface scattering is implemented cor-
rectly “something is still missing.” For example, when GI was included to com-
pensate for the lacking realism of the baby's skin, Hery found that the absence of
skin microstructure was a significant missing element. Consequently, vellus hair
(peach fuzz) was added. In Hery's opinion, missing details like this reveal unnat-
ural visual qualities that audiences may notice without being aware of the actual
cause. Discovering such missing qualities and learning how to compensate for
them is what currently fuels the competition to enhance the simulated appearance
of skin. Novel techniques in movie production arise from the tireless curiosity of
the minds involved; higher quality images come only from endless trials.
4.4 Recent Progress in Subsurface Scattering
Another significant accomplishment in subsurface scattering was published in the
2007 paper entitled
Efficient Rendering of Human Skin
by Eugene d'Eon, David
Luebke and Eric Enderton [d'Eon et al. 07]. Regarding multiple scattering as a
kind of filter of the incident light led the authors to investigate whether a simple
Gaussian filter could be used in place of the multipole reflectance profiles. A
Gaussian filter has the form
1
√
2
v
e
−
r
2
/
2
v
G
(
r
,
v
)=
,
(4.21)
π
where
r
is the distance from the point of incidence and
v
is the Gaussian
variance
or width. Gaussian filters are fast to compute, and have the additional property
that the Fourier transform of a Gaussian is itself a Gaussian. This makes Gaussian
reflectance and transmission profiles ideal for multilayer materials because the
