Attention-Based Depth Distillation with 3D-Aware Positional Encoding for Monocular 3D Object Detection

TL;DR

This paper introduces ADD, a novel attention-based knowledge distillation framework with 3D-aware positional encoding, significantly improving monocular 3D object detection accuracy without extra inference costs.

Contribution

The paper proposes a new knowledge distillation method using a teacher with ground-truth depth, featuring 3D-aware self- and cross-attention modules for better 3D feature learning.

Findings

Achieves state-of-the-art results on KITTI benchmark

No additional inference cost over baseline models

Effective across multiple monocular detectors

Abstract

Monocular 3D object detection is a low-cost but challenging task, as it requires generating accurate 3D localization solely from a single image input. Recent developed depth-assisted methods show promising results by using explicit depth maps as intermediate features, which are either precomputed by monocular depth estimation networks or jointly evaluated with 3D object detection. However, inevitable errors from estimated depth priors may lead to misaligned semantic information and 3D localization, hence resulting in feature smearing and suboptimal predictions. To mitigate this issue, we propose ADD, an Attention-based Depth knowledge Distillation framework with 3D-aware positional encoding. Unlike previous knowledge distillation frameworks that adopt stereo- or LiDAR-based teachers, we build up our teacher with identical architecture as the student but with extra ground-truth depth as input. Credit to our teacher design, our framework is seamless, domain-gap free, easily implementable, and is compatible with object-wise ground-truth depth. Specifically, we leverage intermediate features and responses for knowledge distillation. Considering long-range 3D dependencies, we propose \emph{3D-aware self-attention} and \emph{target-aware cross-attention} modules for student adaptation. Extensive experiments are performed to verify the effectiveness of our framework on the challenging KITTI 3D object detection benchmark. We implement our framework on three representative monocular detectors, and we achieve state-of-the-art performance with no additional inference computational cost relative to baseline models. Our code is available at https://github.com/rockywind/ADD.