Symmetric multi-scale image registration

It is known that the transformations estimated in most of the non-rigid image registration methods are not invertible. This means that the transformation is not one-to-one and also it defines the deformation only in one direction making the registration methods become inconsistent. The symmetric image registration method is a solution to constrain the estimated transformation to become more consistent. This technique promotes the quality of registration significantly. In this paper we present symmetric non-rigid image registration method using multi-scale approach, defining the registration progressively in four different image scales which used result of the previous level as the initial condition for the next level. Our proposed algorithm uses a symmetric cost function which includes forward and backward transformations. Regularization term is used for both forward and reverse deformation fields to control the spatial behavior of the transformation. The results show improving the image similarity and consistency compared to asymmetric methods.