  We propose a 3-D material style transfer framework for reconstructing
invisible (or faded) appearance properties in complex natural materials. Our
algorithm addresses the technical challenge of transferring appearance
properties from one object to another of the same material when both objects
have intricate, noncorresponding color patterns. Eggshells, exoskeletons, and
minerals, for example, have patterns composed of highly randomized layers of
organic and inorganic compounds. These materials pose a challenge as the
distribution of compounds that determine surface color changes from object to
object and within local pattern regions. Our solution adapts appearance
observations from a material property distribution in an exemplar to the
material property distribution of a target object to reconstruct its unknown
appearance. We use measured reflectance in 3-D bispectral textures to record
changing material property distributions. Our novel implementation of spherical
harmonics uses principles from chemistry and biology to learn relationships
between color (hue and saturation) and material composition and concentration
in an exemplar. The encoded relationships are transformed to the property
distribution of a target for color recovery and material assignment.
Quantitative and qualitative evaluation methods show that we replicate color
patterns more accurately than methods that only rely on shape correspondences
and coarse-level perceptual differences. We demonstrate applications of our
work for reconstructing color in extinct fossils, restoring faded artifacts and
generating synthetic textures.
