Ambiguity-aware Point Cloud Segmentation by Adaptive Margin Contrastive Learning

TL;DR

This paper introduces AMContrast3D, an adaptive contrastive learning approach for 3D point cloud segmentation that accounts for point ambiguities, improving accuracy and robustness in indoor scene datasets.

Contribution

It proposes an ambiguity-aware contrastive learning framework with adaptive objectives and a joint training scheme to handle ambiguous points more effectively.

Findings

Significant improvement on S3DIS and ScanNet datasets

Enhanced robustness to ambiguous point labels

Effective ambiguity estimation and refinement mechanisms

Abstract

This paper proposes an adaptive margin contrastive learning method for 3D semantic segmentation on point clouds. Most existing methods use equally penalized objectives, which ignore the per-point ambiguities and less discriminated features stemming from transition regions. However, as highly ambiguous points may be indistinguishable even for humans, their manually annotated labels are less reliable, and hard constraints over these points would lead to sub-optimal models. To address this, we first design AMContrast3D, a method comprising contrastive learning into an ambiguity estimation framework, tailored to adaptive objectives for individual points based on ambiguity levels. As a result, our method promotes model training, which ensures the correctness of low-ambiguity points while allowing mistakes for high-ambiguity points. As ambiguities are formulated based on position discrepancies across labels, optimization during inference is constrained by the assumption that all unlabeled points are uniformly unambiguous, lacking ambiguity awareness. Inspired by the insight of joint training, we further propose AMContrast3D++ integrating with two branches trained in parallel, where a novel ambiguity prediction module concurrently learns point ambiguities from generated embeddings. To this end, we design a masked refinement mechanism that leverages predicted ambiguities to enable the ambiguous embeddings to be more reliable, thereby boosting segmentation performance and enhancing robustness. Experimental results on 3D indoor scene datasets, S3DIS and ScanNet, demonstrate the effectiveness of the proposed method. Code is available at https://github.com/YangChenApril/AMContrast3D.