Optimised coupling of hierarchies in image registration

Image registration algorithms rely on multilevel strategies in order to improve efficiency and robustness. Hierarchies in image resolution, the underlying grids for spline-based transformations, as well as the regularisation parameters are used. This paper deals with the optimisation of the coupling of these hierarchies.An image registration procedure – suitable for 2D polyacrylamide gel electrophoresis images – using piecewise bilinear transformations and an intensity based objective function with a regularisation term based on the elastic deformation energy is described. The resulting nonlinear least squares problem is solved by the Gauss–Newton method.Techniques reminiscent of dynamic programming are used to optimise the coupling of hierarchies in image and transformation resolution. Besides using these techniques to devise an advantageous fixed coupling of both hierarchies, we favour incorporating the dynamic programming ideas into the final registration algorithm. This leads to an adaptive and streamlined approach.Numerical experiments on 2D-PAGE images show that the adaptive registration algorithm is much more reliable than the same algorithm with a fixed coupling of hierarchies. The proposed optimisation procedure for the coupling of hierarchies presents a valuable tool to optimise other registration algorithms.