  It is common to have to process signals or images whose values are cyclic and
can be represented as points on the complex circle, like wrapped phases,
angles, orientations, or color hues. We consider a Tikhonov-type regularization
model to smoothen or interpolate circle-valued signals defined on arbitrary
graphs. We propose a convex relaxation of this nonconvex problem as a
semidefinite program, and an efficient algorithm to solve it.
