In recent years, 3D deformable surface reconstruction
from single images has attracted renewed interest. It has
been shown that preventing the surface from either shrinking
or stretching is an effective way to resolve the ambiguities
inherent to this problem. However, while the geodesic
distances on the surface may not change, the Euclidean
ones decrease when folds appear. Therefore, when applied
to discrete surface representations, such constant-distance
constraints are only effective for smoothly deforming surfaces,
and become inaccurate for more exible ones that
can exhibit sharp folds. In such cases, surface points must
be allowed to come closer to each other.
In this paper, we show that replacing the equality constraints
of earlier approaches by inequality constraints that
let the mesh representation of the surface shrink but not expand
yields not only a more faithful representation, but also
a convex formulation of the reconstruction problem. As a
result, we can...