Graphics Reference
In-Depth Information
(a) (b) (c)
Figure 8.48
Results of single-image separation of a human face. (a) Direct illumination. (b) Indirect
illumination. (c) Subsurface scattering in the skin. (From [Nayar et al. 06]
c
2006 ACM,
Inc. Included here by permission.)
tile. Otherwise the maximum and minimum values will measure to variation in
the object radiance rather than response to high frequency lighting.
A drawback of the single-image method is that the separation is performed as
if the tiles were the individual pixels, and this has the effect of producing lower
resolution separated images. In other words, it is difficult to create high resolu-
tion results. One way around this is to interpolate the values of
L
min
and
L
max
between the tiles, which results in full resolution images. However, the au-
thors advocate simply capturing the images at increased resolution, i.e., higher
than is neededfor the particular application. Figure 8.48 shows the results of
using this method to separate a human face into direct and global components.
The global component includes subsurface scattering. These results reaffirm
the importance of
subsurface scattering in the appearance of human
skin.
As mentioned earlier, the high frequency lighting technique developed by Na-
yar and his collaborators provided the opportunity to examine the effects of direct
and indirect illumination in real objects. For example, Figure 8.49 shows the
separation results of different human hands. The results indicate that the effect
subsurface scattering has on the appearance of skin depends on the concentration
of pigments. This is consistent with the subsurface scattering models developed
by other researchers, as described in Chapter 4. As pigment concentration also
varies in human hair, these results suggest that subsurface scattering is an impor-
tant part of the appearance of hair. Figure 8.50 shows some examples of direct
and global effects in hair.
The conceptual separation of local and global lighting effects were introduced
in Chapter 1 and have been a frequent theme throughout this work. The introduc-
tion of new concepts, such as image based BRDFs and reflectance fields as well
