Graphics Reference
In-Depth Information
Figure 8.55
Scattering in the normal plane from an elliptical blond hair fiber. Illumination comes from
the right. The dark lines show the measured reflectance; the gray regions illustrate the
results of Monte Carlo simulation in the Marschner model. The glints are significant for
this fiber. (From [Marschner et al. 03] c
2003 ACM, Inc. Included here by permission.)
surement set, as a function of
, in the normal plane. The azimuthal functions
N
are constructed to match these measurements. Figure 8.54 contains a sequence
of plots of normal-plane measurements for an increasing incident angle
φ
θ
i
.The
off-specular peaks visible in the first several plots are known as
glints
,andarean
important visual aspect of hair reflection that earlier models did not include. More
dramatic examples of glints can be observed in an elliptical hair fiber, as show in
Figure 8.55.
Glints are caused by caustic effects inside the hair fiber. These secondary
highlights come from “TRT” scattering, and the effect is similar to the reflection
inside water droplets that causes rainbows (
Figure 8.56
)
. Glints are more notice-
able in lighter hair, as there is less pigment to interfere with the transmission of
light. The particular hair fiber used for the normal-plane measurements was more
circular, as is the fiber cross section in Figure 8.56. For fibers with a more ellipti-
cal cross section, which better models real hair, the strength and location of glints
depends on the orientation of the ellipse around the hair-fiber axis. This varies
significantly, especially in “curly” hair, which has a more elliptical cross section,
and is what gives a hair fiber its “distinctive sparkling appearance” according to
the authors. Note that glints normally have the color of the hair, while the primary
specular highlight has the color of the light.
