Higher Resolution Stages

Following the 4mm scale the single best candidate transformation is chosen, and it is only this transformation which is worked with from here on. At the 2mm scale the skews and anisotropic scalings start to become significant. Consequently, these extra Degrees of Freedom (DOF) are progressively introduced by calling the local optimisation method three times: first using only 7 DOF (rigid-body + global scale), then with 9 DOF (rigid-body + independent scalings), then with the full 12 DOF (rigid-body + scales + skews). Since the cost function evaluations take 8 times longer at the 1mm scale than at the 2mm scale, and 512 times longer than at the 8mm scale, only a single pass of the local optimisation is done at the 1mm scale. The result of this single pass is returned as the registration solution, $T^*$.