ICON: Learning Regular Maps Through Inverse Consistency

TL;DR

This paper demonstrates that deep learning models can produce regular, diffeomorphic spatial transformations for image registration using only an inverse consistency loss, without explicit regularizers.

Contribution

It introduces a method leveraging inverse consistency loss and off-grid interpolation to achieve regular maps, challenging the need for explicit regularizers in spatial transformation learning.

Findings

Deep networks with inverse consistency loss produce well-behaved transformations.

The approach achieves competitive registration performance on synthetic and real data.

Regular maps can be learned without explicit regularizers.

Abstract

Learning maps between data samples is fundamental. Applications range from representation learning, image translation and generative modeling, to the estimation of spatial deformations. Such maps relate feature vectors, or map between feature spaces. Well-behaved maps should be regular, which can be imposed explicitly or may emanate from the data itself. We explore what induces regularity for spatial transformations, e.g., when computing image registrations. Classical optimization-based models compute maps between pairs of samples and rely on an appropriate regularizer for well-posedness. Recent deep learning approaches have attempted to avoid using such regularizers altogether by relying on the sample population instead. We explore if it is possible to obtain spatial regularity using an inverse consistency loss only and elucidate what explains map regularity in such a context. We find that deep networks combined with an inverse consistency loss and randomized off-grid interpolation yield well behaved, approximately diffeomorphic, spatial transformations. Despite the simplicity of this approach, our experiments present compelling evidence, on both synthetic and real data, that regular maps can be obtained without carefully tuned explicit regularizers, while achieving competitive registration performance.