self-shadowing attributes are matched nicely and generalize
well to the second illumination condition. One limitation for
this material is that it has substantial low-frequency content
in its texture, which our small sample area did not capture in
the CT imaging, leading to a slightly more uniform appearance in our tiled material. Figure 6(d) demonstrates the
ability of our volumetric appearance model to capture the
material’s thick, fuzzy appearance.
A 3D, physically based model also allows more meaningful editing than image-based methods. In Figure 7, we extend
the gabardine model with a spatially varying albedo value.
The albedo is computed as a function of orientation, so that
fibers in the warp and weft are assigned different colors.
With blue warp and white weft a fabric similar to denim is
produced, though made of wool rather than cotton.
We have demonstrated a new, multimodal approach to making realistic volume models of cloth that capture both the 3D
structure evident in close-up renderings and the reflectance
evident in farther-away views. Unlike previous methods for
capturing cloth appearance using BTFs, our method explicitly models the 3D structure of the material and, interestingly,
is able to capture the directional reflectance of the material
automatically because of this structure.
Our modeling approach uses CT imaging where it is
strongest, in measuring 3D structure, and it uses photo-
graphs where they are strongest, in measuring color and
with a low-frequency environment map. The validation pair
accurately predicts the texture under a different lighting condi-
tion, which involves a strong luminaire at the top. In the draped
configuration in Figure 6(b), the volume model captures sub-
tle foreshortening effects and the silhouette appearance, as
well as the subtle variations in texture across the surface. The
appearance at the cut edge gives the proper impression of the
thickness of the fabric (compare to the very thin satin material),
which is a perennial difficulty with surface models.
Velvet, a material with a cut pile (like a carpet), has a visible
surface composed of fibers that stick up from the base material. It has a very distinctive appearance, with a characteristic
grazing-angle highlight. The appearance of velvet depends
on how the fibers are brushed, and our random tile rotation
method produces randomly brushed velvet. In Figure 6(c), we
demonstrate how our model reproduces the characteristic
velvet highlights. Further, the edges and silhouettes convey
the considerable thickness and weight of this material.
Felt is a nonwoven textile consisting of a disorganized
layer of matted fibers. The thickness and fuzziness of this
material are important appearance attributes that are generally difficult to model and render. Since felt does not exhibit
an overall specular highlight, we used a flat patch for appearance matching; because of limited depth of field, we limited
the matching region to a thin rectangle where the photograph is in good focus. The illumination conditions for the
appearance matching and the validation are the same as
those for the gabardine. The color and the contrast due to
Figure 6. Fabrics in draped configurations with our volumetric appearance model: (a) silk satin, (b) gabardine, (c) velvet, and (d) felt.