ically speed up alignment, and in general not
 degrade performance much. [sig] controls image smoothing, sig=2 gives
 good performance, setting sig too low causes loss of information and too
 high will violate the linearity assumption. [epsilon] defines the
 stopping criteria, use to adjust performance versus speed tradeoff.
 [lambda] is a regularization term that causes small transforms to be
 favored, in general any small non-zero setting of lambda works well.
 [outThr] is a threshold beyond which 