Shape Reconstruction  of 3D  Bilaterally Symmetric Surfaces

                    Ilan Shimshoni 

               Technion, Haifa, Israel

The talk presents a new approach for shape recovery based on
integrating geometric and photometric information.  We consider 3D
bilaterally symmetric objects, that is, objects which are symmetric
with respect to a plane (e.g., faces), and their reconstruction from a
single image.  Both the viewpoint and the illumination are not
necessarily frontal.  Furthermore, no correspondence between symmetric
points is required.

The basic idea is that an image taken from a general, non frontal
viewpoint, under non-frontal illumination can be regarded as a pair of
images. Each image of the pair is one half of the object, taken from
different viewing positions and with different lighting directions.
Thus, one-image-variants of geometric stereo and of photometric stereo
can be used.  Unlike the separate invocation of these approaches,
which require point correspondence between the two images, we show
that integrating the photometric and geometric information suffice to
yield a dense correspondence between pairs of symmetric points, and as
a result, a dense shape recovery of the object. Furthermore, the
unknown lighting and viewing parameters, are also recovered in this
process.

Unknown distant point light source, Lambertian surfaces, unknown
constant albedo, and weak perspective projection are assumed.  The
method has been implemented and tested experimentally on simulated and
real data.

Joint work with: Yael Moses and Michael Lindenbaum.