Inlier-Centric Post-Training Quantization for Object Detection Models

Object detection is pivotal in robotics, but its immense computational demands make the models slow and power-hungry, underscoring the need for quantization. However, when the quantization is applied in practice, cluttered backgrounds and irregular object morphologies cause redundant activations (or anomalies) that inflate precision requirements and waste bit capacity, hindering the preservation of informative features. Moreover, without a clear criterion for defining such anomalies, attempts to exclude or mitigate them often distort useful features. To address this problem, we present InlierQ, an inlier-centric post-training quantization approach that establishes a general criterion to differentiate anomalies from informative inliers. Specifically, InlierQ computes gradient-aware volume saliency scores, classifies each volume as an inlier or outlier, and fits a posterior distribution over these scores using the Expectation–Maximization (EM) algorithm. This design effectively suppresses the influence of outliers while preserving informative inlier features. InlierQ is a label-free, drop-in method and uses only 64 samples for calibration. Experiments on the COCO and nuScenes benchmarks demonstrate consistent reductions in quantization errors across camera-based (2D and 3D) and LiDAR-based (3D) object detection.