This document details efforts undertaken by the National Institute of Standards and Technology (NIST) to develop measurements and a protocol for the evaluation of contactless (touchless) fingerprint acquisition devices. Contactless fingerprint capture differs fundamentally from legacy contact fingerprinting methods, and poses novel problems for image quality evaluation and challenges relative to interoperability with contact fingerprints that populate large repositories maintained by law enforcement and Federal Government organizations. For contact acquisition, the fingerprint impression is a first-order transfer of the 3D friction ridge structure to the recording surface. The third dimension of the curved finger surface is effectively removed by pressure against the planar recording surface. The 3D topography of the ridges and furrows are transferred with low ambiguity to the recording surface as dark ridges (points of contact) and lighter furrows (lesser or no contact). Contactless images by comparison, in most cases, are third-order renderings of an original photographic representation, itself a 2D optical projection of the 3D structure of the finger. The appearance of this projection is subject to variability as low- or moderately-controlled lighting interacts with the 3D geometry of the finger, the friction ridge structure superimposed on the finger, and the geometry of the presentation of the finger to the contactless device. The photograph must then be subjected to various image processing methods to infer the ridge structure for rendering as a fingerprint similar in appearance to legacy contact captures. The rendering process is the source of numerous errors relative to contact captures. Despite problems with image quality, this early study finds contactless fingerprints of the devices examined to be usable in some applications, with qualifications, including one- to-many matching against small databases.
Special Publication (NIST SP) - 500-305
contactless fingerprinting, friction ridge, fingerprint device interoperability