Structured Feature Similarity With Explicit Feature Map

Feature matching is a fundamental process in a variety of computer vision tasks. Beyond the standard L2 metric, various methods to measure similarity between features have been proposed mainly on the assumption that the features are defined in a histogram form. On the other hand, in a field of image quality assessment, SSIM produces effective similarity between images, taking the place of L2 metric. In this paper, we propose a feature similarity measurement method based on the SSIM. Unlike the previous methods, the proposed method is built on not a histogram form but a tensor structure of a feature array extracted such as on spatial grids, in order to construct effective SSIM-based similarity measure of high robustness which is a key requirement in feature matching. In addition, we provide the explicit feature map such that the proposed similarity metric is embedded as a dot product. It contributes to significant speedup in similarity measurement as well as to feature transformation toward an effective vector form to which linear classifiers are directly applicable. In the experiments on various tasks, the proposed method exhibits favorable performance in both feature matching and classification.