Robust Structured Declarative Classifiers for Point Clouds

Abstract

Deep neural networks for 3D point cloud classification, such as PointNet, have been demonstrated to be vulnerable to adversarial attacks. Current adversarial defenders often learn to denoise the (attacked) point clouds by reconstruction, and then feed them to the classifiers as input. In contrast to the literature, we propose a novel bilevel optimization framework for robust point cloud classification, where the internal optimization can effectively defend the adversarial attacks as denoising and the external optimization can learn the classifiers accordingly. As a demonstration, we further propose an effective and efficient instantiation of our approach, namely, Lattice Point Classifier (LPC), based on structured sparse coding in the permutohedral lattice and 2D convolutional neural networks (CNNs) that integrates both internal and external optimization problems into end-to-end trainable network architectures. We demonstrate state-of-the-art robust point cloud classification performance on ModelNet40 and ScanNet under seven different attackers. Our demo code is available at: https://github.com/Zhang-VISLab .