Generalizations of the Normalized Radon Cumulative Distribution Transform for Limited Data Recognition
This work addresses the challenge of small data recognition in fields like filigranology, offering incremental improvements to existing normalization methods.
The paper tackles the problem of recognizing patterns in limited data, such as watermarks, by developing generalized normalizations of the Radon cumulative distribution transform to handle affine transformations, achieving near-perfect classification accuracies in experiments with 2D images, 3D shapes, and 3D rotation matrices.
The Radon cumulative distribution transform (R-CDT) exploits one-dimensional Wasserstein transport and the Radon transform to represent prominent features in images. It is closely related to the sliced Wasserstein distance and facilitates classification tasks, especially in the small data regime, like the recognition of watermarks in filigranology. Here, a typical issue is that the given data may be subject to affine transformations caused by the measuring process. To make the R-CDT invariant under arbitrary affine transformations, a two-step normalization of the R-CDT has been proposed in our earlier works. The aim of this paper is twofold. First, we propose a family of generalized normalizations to enhance flexibility for applications. Second, we study multi-dimensional and non-Euclidean settings by making use of generalized Radon transforms. We prove that our novel feature representations are invariant under certain transformations and allow for linear separation in feature space. Our theoretical results are supported by numerical experiments based on 2d images, 3d shapes and 3d rotation matrices, showing near perfect classification accuracies and clustering results.