PTQAT: A Hybrid Parameter-Efficient Quantization Algorithm for 3D Perception Tasks

TL;DR

PTQAT is a hybrid quantization algorithm that combines post-training and quantization-aware training to efficiently deploy 3D perception models with minimal performance loss and reduced training costs.

Contribution

The paper introduces PTQAT, a hybrid quantization method that selectively fine-tunes critical layers, achieving near-QAT performance with less training and supporting various models and bit widths.

Findings

Outperforms QAT baselines on 3D perception tasks.

Achieves 0.2%-1.0% improvements in key metrics.

Freezes nearly 50% of layers for efficiency.

Abstract

Post-Training Quantization (PTQ) and Quantization-Aware Training (QAT) represent two mainstream model quantization approaches. However, PTQ often leads to unacceptable performance degradation in quantized models, while QAT imposes substantial GPU memory requirements and extended training time due to weight fine-tuning. In this paper, we propose PTQAT, a novel general hybrid quantization algorithm for the efficient deployment of 3D perception networks. To address the speed accuracy trade-off between PTQ and QAT, our method selects critical layers for QAT fine-tuning and performs PTQ on the remaining layers. Contrary to intuition, fine-tuning the layers with smaller output discrepancies before and after quantization, rather than those with larger discrepancies, actually leads to greater improvements in the model's quantization accuracy. This means we better compensate for quantization errors during their propagation, rather than addressing them at the point where they occur. The proposed PTQAT achieves similar performance to QAT with more efficiency by freezing nearly 50% of quantifiable layers. Additionally, PTQAT is a universal quantization method that supports various quantization bit widths (4 bits) as well as different model architectures, including CNNs and Transformers. The experimental results on nuScenes across diverse 3D perception tasks, including object detection, semantic segmentation, and occupancy prediction, show that our method consistently outperforms QAT-only baselines. Notably, it achieves 0.2%-0.9% NDS and 0.3%-1.0% mAP gains in object detection, 0.3%-2.0% mIoU gains in semantic segmentation and occupancy prediction while fine-tuning fewer weights.