ISO/IEC 29794-4:2024
(Main)Information technology — Biometric sample quality — Part 4: Finger image data
Information technology — Biometric sample quality — Part 4: Finger image data
ISO/IEC 29794-4:2017 establishes - terms and definitions for quantifying finger image quality, - methods used to quantify the quality of finger images, and - standardized encoding of finger image quality, for finger images at 196,85 px/cm spatial sampling rate scanned or captured using optical sensors with capture dimension (width, height) of at least 1,27 cm × 1,651 cm.
Technologies de l'information — Qualité d'échantillon biométrique — Partie 4: Données d'image de doigt
General Information
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Standards Content (Sample)
International
Standard
ISO/IEC 29794-4
Second edition
Information technology —
2024-09
Biometric sample quality —
Part 4:
Finger image data
Technologies de l'information — Qualité d'échantillon
biométrique —
Partie 4: Données d'image de doigt
Reference number
© ISO/IEC 2024
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© ISO/IEC 2024 – All rights reserved
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Conformance . 2
6 Finger image quality measures . 3
6.1 Overview .3
6.1.1 General .3
6.1.2 Methods for mapping to the desired value range .3
6.1.3 Constituent of local quality measures .4
6.1.4 Constituent of global quality measures .4
6.1.5 Image preprocessing .4
6.1.6 Image examples .7
6.2 Normative contributive quality components .7
6.2.1 General .7
6.2.2 Orientation certainty level .7
6.2.3 Local clarity .9
6.2.4 Frequency domain analysis (FDA) .14
6.2.5 Ridge valley uniformity . 15
6.2.6 Orientation flow .17
6.2.7 MU .19
6.2.8 MMB .19
6.2.9 Minutiae count in finger image .19
6.2.10 Minutiae count in centre of mass region . 20
6.2.11 Minutiae quality based on local image mean . 20
6.2.12 Minutiae quality based on local orientation certainty level.21
6.2.13 Region of interest image mean . 22
6.2.14 Region of interest orientation map coherence sum .24
6.2.15 Region of interest relative orientation map coherence sum . 25
6.2.16 Quality feature vector composition . 25
6.3 Non-normative quality measures . 28
6.3.1 General . 28
6.3.2 Radial power spectrum . 29
6.3.3 Gabor filter bank. 30
6.4 Unified quality score .32
6.4.1 Methodology for combining quality components .32
6.4.2 Training method .32
7 Finger image quality block . .33
7.1 Binary encoding . 33
7.2 XML encoding . 33
7.3 Quality algorithm identifiers . 33
Annex A (normative) Conformance test assertions .35
Annex B (informative) Factors influencing fingerprint image quality.57
Annex C (informative) Area consideration .59
Bibliography .60
© ISO/IEC 2024 – All rights reserved
iii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations,
governmental and non-governmental, in liaison with ISO and IEC, also take part in the work.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of document should be noted. This document was drafted in accordance with the editorial rules of the ISO/
IEC Directives, Part 2 (see www.iso.org/directives or www.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any
claimed patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had not
received notice of (a) patent(s) which may be required to implement this document. However, implementers
are cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents and https://patents.iec.ch. ISO and IEC shall not be held
responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 37, Biometrics.
This second edition cancels and replaces the first edition (ISO/IEC 29794-4:2017), which has been technically
revised.
The main changes are as follows:
— algorithms for normalization of finger image quality components have been added, along with new quality
algorithm identifiers for the unique identification of the quality measures defined in this document;
— Annex A has been technically revised to reflect a new conformance test set.
A list of all parts in the ISO/IEC 29794 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
www.iec.ch/national-committees.
© ISO/IEC 2024 – All rights reserved
iv
Introduction
This document specifies finger image quality measures. A reference implementation of the normative
measures — NFIQ 2 — is available at Reference [16], which is described in more detail by the developers in
Reference [1].
The quality of finger image data is determined by the degree to which the finger image data fulfils
specified requirements for the targeted application. Information on quality is therefore useful in many
applications. ISO/IEC 19784-1 allocates a quality field and specifies the allowable range for the scores, with
a recommendation that the score be divided into four categories with a qualitative interpretation for each
category. Finger image quality fields are provided in the finger image data interchange formats standardized
in ISO/IEC 19794-4 and ISO/IEC 39794-4. Finger feature data interchange formats standardized in
ISO/IEC 19794-2, ISO/IEC 19794-3, ISO/IEC 19794-8 and ISO/IEC 39794-2 provide finger image quality
fields for the source image. To facilitate the interpretation and interchange of finger image quality scores,
this document specifies how to calculate the finger image quality score of plain finger images with a spatial
sampling rate of 196,85 px/cm and a bit depth of 8 bit for the greyscale pixel intensity values scanned from
inked fingerprint cards or captu
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