扩充车牌可读性数据集,提升真实场景识别准确率。
LPLCv2: An Expanded Dataset for Fine-Grained License Plate Legibility Classification

- 扩展原数据集至三倍以上规模,新增标注信息。
- 新方法使模型测试集F1达89.5%,显著优于旧版。
- 支持细粒度标注,适合真实交通场景研究者使用。
现代自动车牌识别(ALPR)系统在受控环境下表现优异,但在真实场景中仍面临成像质量差、压缩伪影和摄像头安装不当等问题。尽管已有专门基准用于识别不可读车牌,但其影响受限于数据量小和标注误差。本文将原始基准扩展至三倍以上规模,新增两天采集数据,修正标注并引入新标签。车牌级标注包括边界框、文本内容及可读性等级,车辆级标注包含品牌、型号、类型和颜色,图像级标注涵盖摄像头身份、拍摄条件(如雨天、故障摄像头)、获取时间与日期编号。我们提出基于指数移动平均的损失函数与优化学习率调度策略,有效纠正测试常见错误。该基线模型在测试集上达到89.5%的F1分数,大幅超越先前最佳水平。此外,我们设计新评估协议以明确处理训练与测试集间的摄像头污染问题,结果显示影响较小。数据集与代码已公开于https://github.com/lmlwojcik/LPLCv2-Dataset。
原文摘要 · Abstract (English)
Modern Automatic License Plate Recognition (ALPR) systems achieve outstanding performance in controlled, well-defined scenarios. However, large-scale real-world usage remains challenging due to low-quality imaging devices, compression artifacts, and suboptimal camera installation. Identifying illegible license plates (LPs) has recently become feasible through a dedicated benchmark; however, its impact has been limited by its small size and annotation errors. In this work, we expand the original benchmark to over three times the size with two extra capture days, revise its annotations and introduce novel labels. LP-level annotations include bounding boxes, text, and legibility level, while vehicle-level annotations comprise make, model, type, and color. Image-level annotations feature camera identity, capture conditions (e.g., rain and faulty cameras), acquisition time, and day ID. We present a novel training procedure featuring an Exponential Moving Average-based loss function and a refined learning rate scheduler, addressing common mistakes in testing. These improvements enable a baseline model to achieve an 89.5% F1-score on the test set, considerably surpassing the previous state of the art. We further introduce a novel protocol to explicitly addresses camera contamination between training and evaluation splits, where results show a small impact. Dataset and code are publicly available at https://github.com/lmlwojcik/LPLCv2-Dataset.
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