FACIAL SOFT BIOMETRICS - Library of Ph.D. Theses | EURASIP

7– Not requiring the individual’s cooperation: Consent and contribution from the subject aregenerally not needed.– Preserving human privacy: The stored signatures are visually available to everyone andserve in this sense privacy.The plethora or utilities has motivated an increasing number of research activities related tosoft biometrics. We give an overview of scientific work gaining from the benefits related to softbiometrics.Related work We here outline work, pertinent to soft biometrics. This overview does not claimto be an exhaustive state of the art, but rather a highlight selection on performed scientific studies.Soft biometrics is a relatively novel topic and related work enfolds over several research fields.Recent work can be mainly classified in three research fields:1. The first and largest field includes the study and identification of traits and associated imageprocessing algorithms for classification and detection of such.2. The second fast growing field identifies operational scenarios for the aforementioned algorithmsand provides experimental results for such scenarios.3. The third and smallest field comprises of the global and theoretical investigation of theemployment of soft biometrics applications and related studies.Scientific works belonging to the first field cover algorithms for traits such as iris pattern, seein [SBS10], or facial marks, see in [JP09].The second field can be sub-classified in subgroups which differentiate the way soft biometricsare employed, as stand–alone systems, as pre-filtering mechanisms of bigger systems, or as fusedparallel systems. Related scenarios include continuous authentication [NPJ10], video surveillancesee [DFBS09], [FDL + 10], [MKS10], person verification [ZESH04] and moreover person identification[PJ10]. An interesting recent associated scenario for SBS based person identification isthe recognition of faces in triage images of mass disaster situations [CO11].Finally the third field involves studies on the placement of soft biometrics in applications suchas forensics [JKP11] and human metrology [ACPR10].Bag of facial soft biometrics for human identificationWe consider the case where a SBS can distinguish between a set of traits (categories), whichset is large enough to allow for the classification that achieves human identification. The conceptof person identification based on soft biometrics originates in the way humans perform face recognition.Specifically human minds decompose and hierarchically structure complex problems intofractions and those fractions into further sub-fractions, see [Ley96], [Sim96]. Consequently facerecognition performed by humans is the division of the face in parts, and subsequent classificationof those parts into categories. Those categories can be naturally of physical, adhered or behavioralnature and their palette includes colors, shapes or measurements, what we refer to here as softbiometrics. The key is that each individual can be categorized in terms of such characteristics,by both humans or by image processing algorithms. Although features such as hair, eye and skincolor, facial hair and shape, or body height and weight, gait, cloth color and human metrologyare generally non distinctive, a cumulative combination of such features provides an increasinglyrefined and explicit description of a human. SBSs for person identification have several advantagesover classical biometric systems, as of non intrusiveness, computational and time efficiency,human compliance, flexibility in pose- and expression-variance and furthermore an enrolment freeacquirement in the absence of consent and cooperation of the observed person. Soft biometricsallow for a reduced complexity determination of an identity. At the same time though, the named