Using reflectance symmetries to reduce inherent photometric stereo ambiguity
Ondrej Drbohlav
CMP Prague, Czech Republic
Photometric stereo with uncalibrated lights determines surface
orientations ambiguously up to any regular transformation. If the
surface reflectance model is separable with respect to the
illumination and viewing directions, its inherent symmetries enable
to design two previously unrecognized constraints on normals that
reduce this ambiguity. The two constraints represent projections of
normals onto planes perpendicular to the viewing and illumination
directions, respectively. We identify the classes of transformations
that leave each constraint invariant.
We construct the constraints using polarization measurement under
the assumption of separable reflectance model for smooth
dielectrics.
We verify that applying the first constraint together with the
integrability constraint results in bas-relief ambiguity, while
application of the second constraint on integrable normals reduces
the ambiguity to convex/concave ambiguity. Importantly, the latter
result is also obtained when the first and second constraints alone
are combined.