Touchless fingerprint recognition represents a rapidly growing field of research which has been studied for more than a decade. Through a touchless acquisition process, many issues of touch-based systems are circumvented, e.g., the presence of latent fingerprints or distortions caused by pressing fingers on a sensor surface. However, touchless fingerprint recognition systems reveal new challenges. In particular, a reliable detection and focusing of a presented finger as well as an appropriate preprocessing of the acquired finger image represent the most crucial tasks. Also, further issues, e.g., interoperability between touchless and touch-based fingerprints or presentation attack detection, are currently investigated by different research groups. Many works have been proposed so far to put touchless fingerprint recognition into practice. Published approaches range from self identification scenarios with commodity devices, e.g., smartphones, to high performance on-the-move deployments paving the way for new fingerprint recognition application scenarios.This work summarizes the state-of-the-art in the field of touchless 2D fingerprint recognition at each stage of the recognition process. Additionally, technical considerations and trade-offs of the presented methods are discussed along with open issues and challenges. An overview of available research resources completes the work.

非接触式指纹识别代表了一个快速发展的研究领域，已经研究了十多年。通过非接触式采集过程，避免了许多基于触摸的系统问题，例如，潜在的指纹的存在或由于将手指按在传感器表面上而导致的变形。然而，非接触式指纹识别系统揭示了新的挑战。特别是，对所显示手指的可靠检测和聚焦以及对所获取手指图像的适当预处理代表了最关键的任务。同样，其他研究小组目前正在研究其他问题，例如非接触式和基于接触式指纹之间的互操作性或呈现攻击检测。迄今为止，已经提出了许多将非接触式指纹识别付诸实践的工作。已发布的方法涵盖了从带有智能手机等商品设备的自我识别场景到高性能的移动部署，为新的指纹识别应用场景铺平了道路。这项工作总结了非接触式领域的最新技术在识别过程的每个阶段进行2D指纹识别。此外，还讨论了所提出方法的技术考虑因素和权衡取舍以及未解决的问题和挑战。可用研究资源的概述完成了这项工作。这项工作总结了在识别过程的每个阶段非接触式2D指纹识别领域的最新技术。此外，还讨论了所提出方法的技术考虑因素和权衡取舍以及未解决的问题和挑战。可用研究资源的概述完成了这项工作。这项工作总结了在识别过程的每个阶段非接触式2D指纹识别领域的最新技术。此外，还讨论了所提出方法的技术考虑因素和权衡取舍以及未解决的问题和挑战。可用研究资源的概述完成了这项工作。