In this paper we pursue the task of aligning an ensemble
of images in an unsupervised manner. This task has
been commonly referred to as “congealing” in literature.
A form of congealing, using a least-squares criteria, has
been recently demonstrated to have desirable properties
over conventional congealing. Least-squares congealing
can be viewed as an extension of the Lucas & Kanade (LK)
image alignment algorithm. It is well understood that the
alignment performance for the LK algorithm, when aligning
a single image with another, is theoretically and empirically
equivalent for additive and compositional warps. In this paper
we: (i) demonstrate that this equivalence does not hold
for the extended case of congealing, (ii) characterize the
inherent drawbacks associated with least-squares congealing
when dealing with large numbers of images, and (iii)
propose a novel method for circumventing these limitations
through the application of an inverse-compositional strat...