How do biometric registration systems work

ISO / IEC exchange formats for biometric data

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1 ISO / IEC exchange formats for biometric data Olaf Henniger and Ulrich Waldmann Fraunhofer Institute for Secure Information Technology, Rheinstr. 75, Darmstadt {henniger summary. This article provides an overview of the standardization of exchange formats for biometric data in the multi-part standard ISO / IEC Standardized data exchange formats are intended to ensure the comparability of similar biometric data that have been recorded and processed with different biometric components. This is particularly relevant for the biometric reference and verification data in smartcard-based biometric systems (both off-card and on-card matching). 1 Overview This article provides an overview of the current state of development of ISO / IEC 19794, a multi-part standard for exchange formats for biometric data that is currently being developed by ISO / IEC JTC 1 / SC 37 / WG 3. ISO / IEC includes e.g. Z. the following parts: Part 1: Framework [ISO], Part 2: Finger Minutiae Data [ISO], Part 3: Finger Pattern Spectral Data [ISO], Part 4: Finger Image Data [ISO], Part 5: Face Image Data [ISO], Part 6: Iris Image Data [ISO], Part 7: Signature / Sign Time Series Data [ISO], Part 8: Finger Pattern Skeletal Data [ISO], Part 9: Vascular Image Data [ISO], Part 10: Hand Geometry Silhouette Data [ISO] and Part 11: Signature / Sign Processed Dynamic Data [ISO]. [ISO] defines the general properties and conditions of use for biometric data exchange formats. Each of the other parts defines (at least) one format type for a specific biometric technology. If necessary, additional parts can be added if the criteria for creating new parts specified in [ISO] are met. The development of the individual parts of ISO / IEC in recent years is shown in Figure 1 based on the level of standardization achieved in each case. The periods between the meetings are used to develop and comment on the drafts and to vote on the status quo. In 2005 could

2 Orlando Ottawa Rome Sydney Seoul Paris South Africa Part Title Framework FDIS? 2 finger minutiae data FDIS IS? 3 finger pattern spectral data FDIS? 4 finger image data FDIS IS? 5 Face image data FDIS IS? 6 Iris image data FDIS IS? 7 Signature / sign time series data? 8 finger pattern skeletal data? 9 Vascular image data? 10 hand geometry silhouette data? 11 Signature / sign processed dynamic data? = New Work Item Proposal, = Working Draft, = Committee Draft, = Final Committee Draft, FDIS = Final Draft International Standard, IS = International Standard Figure 1 Development of the parts of ISO / IEC some biometric data formats reach the status of international standards and finally to be published. [ISO] differentiates between the following three processing stages of biometric data (see Figure 2): The recorded (raw) data is data as it is supplied by biometric sensors. Intermediate (image or behavioral) data are data that have already been preprocessed and formatted for data exchange, but are not suitable for direct computer-aided comparison. Feature data are data that are preprocessed and formatted for data exchange and are also suitable for direct computer-aided comparison. In ISO / IEC formats are defined for intermediate data and for feature data with the aim that biometric data of the same type, which are recorded and processed with different biometric components, can be compared with one another in open systems. The standardized data formats can also be used in conjunction with proprietary data, which can accelerate or deepen the comparison of features if reference and verification data come from the same source. Limited storage and computing capacities can limit the application range of certain data exchange formats. Since most preprocessing and feature extraction methods require more computing resources than are available on smart cards today, sensor feature extraction Recorded (raw) data Intermediate (image or behavioral) data Data preprocessing Data acquisition Feature data Figure 2 Processing stages of biometric data 2

3, feature data are stored on the smart card as biometric reference data for on-card matching. In the case of off-card matching, the smart card only serves as a decentralized storage medium for the biometric reference data and either feature data or intermediate data, from which feature data must be extracted for comparison outside the smart card, are stored as reference data on the smart card. After this overview of the standardization of biometric data exchange formats in ISO / IEC, the article is further structured as follows: Section 2 deals with the possible embedding of biometric data in a CBEFF framework; Section 3 describes the exchange formats for biometric data in detail and Section 4 provides a summary. 2 Embedding in the CBEFF framework The Common Biometric Exchange Formats Framework (CBEFF) [ISO] defines general framework conditions for exchange formats for biometric data and describes an abstract framework format (Biometric Information Record) for biometric data. This frame format contains a header (Standard Biometric Header), a body (Biometric Data Block) and at the end an optional electronic signature block (see Figure 3). Abstract data elements are defined for the head part, which designate the biometric type (e.g. fingerprint), the format owner and format type of the biometric data contained in the body part and other attributes of the biometric data. The Biometric Data Block is intended for the actual biometric data, the structure of which is not further defined in the CBEFF specification. Standard Biometric Header Biometric Data Block Signature Block defines abstract data elements and undefined values ​​in CBEFF e.g. B. ISO / IEC data formats undefined in CBEFF optional Figure 3 Structure of a Biometric Information Record In [ISO] so-called cartridge formats are specified. These are concrete CBEFF formats that translate the abstract definitions of the CBEFF structure and the header elements for various areas of application. The exchange formats according to ISO / IEC can be embedded in the specified cartridge formats and take the place of the biometric data block in the biometric information record. The cartridge formats differ in the use and coding of the CBEFF header elements. The format owner and format type elements are stipulated in every cartridge format and serve to identify the format of the biometric data it contains. [ISO] defines the registration procedures for biometric organizations, data formats, products and patron formats. IBIA (International Biometric Industry Association) is defined as the CBEFF registration authority. A registered biometric organization can define both biometric data formats and its own patron formats and register them with IBIA. The organization ISO / IEC JTC 1 / SC 37 is registered with IBIA as the format owner and is the owner of both the data standardized in ISO / IEC 3

4 formats as well as the cartridge formats specified in ISO / IEC. The format owner identifier of SC 37 is The format type identifier for the individual data exchange formats are specified in the individual parts of ISO / IEC. The data formats according to ISO / IEC can also be used without the CBEFF framework. Some of the formats were developed as independent data structures and can contain all the necessary information about the biometric data in their data sets themselves. For this reason, information that can also be found in the CBEFF header is duplicated in some data exchange formats. 3 Exchange formats for biometric data 3.1 Fingerprints Finger Minutiae Data [ISO] describes data formats for encoding fingerprint minutiae. Fingerprint minutiae are feature data used in various fingerprint recognition systems, originally in proprietary formats. The standardized minutiae format is of great importance, since minute-based systems for fingerprint recognition have the largest market share in biometric products. The formats specified in [ANSI00] and [DIN66400] have been integrated into [ISO]. In addition to a general minute data format, [ISO] describes special compact minute data formats that are to be used in the case of on-card matching. The compact data formats are largely free of redundancy and concentrate on the most compact possible coding of the mathematical quantities required for a feature comparison. With the normal and the compact minutiae format, the user is given two different types of coding to choose from. [ISO] claims to ensure the interoperability of feature extraction and feature comparison algorithms from different manufacturers and the compatibility of reference and verification data generated with different feature extraction algorithms. Since feature extraction algorithms are viewed as intellectual property, in addition to the precise specification of the data formats, only general information on the position and angle of minutiae, but no calculation rules for their determination can be found in [ISO]. Different methods for determining position and angle can impair interoperability. A first comparative study of minute-based fingerprint recognition systems [ILO04] has shown that most of the tested combinations of minute products are not interoperable and lead to a loss in recognition performance, although the exchanged data all satisfied a draft by [ISO]. Obviously, there is a need to specify requirements for the data content more precisely in order to achieve the comparability of data sets from different sources. 4th

5 3.1.2 Finger Pattern Spectral Data Many, but not all, fingerprint recognition systems use minutiae as feature data to be compared, e.g. For example, in Bioscrypt products, pattern recognition algorithms are used to compare features. [ISO] defines a format for fingerprint data based on line patterns. The mathematical strategy for determining the parameters is as follows: division of the fingerprint into small cells within which the fingerprint lines run approximately straight and parallel, analysis of the gray level value change as a sine function perpendicular to the line pattern. On the one hand, the data format is much more space-saving than pixel images, but on the other hand (in contrast to minutiae) it still represents the entire fingerprint image. The format is also intended for simpler sensors with a lower image resolution of only 200 dpi and is suitable for fingerprint recognition systems with limited storage capacity for biometric data. In addition to the general data format, [ISO] defines a special compact data format for use in smart cards for off-card and on-card matching. Finger Pattern Skeletal Data [ISO] defines a feature data format based on the skeleton representation of the papillary lines. The data sets contain direction codes of line elements of the line skeleton. The start and end points of the line elements are marked as real or virtual minutiae, and the course of a line element from the start to the end point is coded by successive changes in direction. Each line in the line skeleton image is coded as a polygon. All line codes together form the skeletal description of the fingerprint pattern. The format offers a compact form of fingerprint feature data from which skeletal fingerprint images can still be reconstructed. The data record size can be up to 500 bytes. In addition to the general data format, [ISO] also defines two card-related data formats, a normal format and a compact format. The standard defines fixed values ​​for most elements in the header of the card formats Finger Image Data [ISO] defines a data format for complete images of prints of fingers or palms. Data records contain a header to identify the data they contain. The actual fingerprint images are pixel-oriented grayscale images in standard formats with or without compression. Use of JPEG 2000 as the compression algorithm is recommended. A normative annex contains requirements for image quality. The minimum resolution of the fingerprint sensor in the horizontal and vertical direction is 500 dpi. The fingerprint image data format is distinguished by an exact fingerprint identification and a high quality of the image data, so that any type of fingerprint feature data can later be extracted from stored image data sets. The 5th

6 format is not suitable for the direct computer-aided comparison of data sets. Before a comparison is possible, feature data must be extracted from the fingerprint images. Since this is not possible with smart cards at the current stage of development, the format is not suitable for fingerprint-on-card matching. This data format is used in the forensic field to capture fingerprint images e.g. B. for AFIS (Automated Fingerprint Identification System) systems to save, whereby the size of the data records is hardly subject to any restrictions. The image data format is currently considered to be the only interoperable exchange format for fingerprint data. ICAO (International Civil Aviation Organization) therefore recommends the image data format as the format for fingerprint data, which can optionally (in addition to the mandatory facial image data) be stored in machine-readable travel documents. 3.2 Face Image Data Uniform formats for face images are specified in [ISO]. The data records contain a header to identify the data they contain. The actual facial images are pixel-based grayscale images or colored facial images in standard formats such as JPEG or JPEG.There are two different image formats: Full Frontal: A format for frontal images (data record size approx. 11 kbyte) Token Frontal: A compact format for frontal images (data record size approx. 6 kbyte). The position of the eyes plays an important role for the Token Frontal format: The Token Frontal images are normalized to a uniform eye relief to reduce the image size. Both image formats are compressed with JPEG or JPEG. By choosing between the two image data formats, the user has the option of either prioritizing requirements for image quality or restrictions on storage space. [ISO] also defines optional feature points such as eye and nostril centers in facial images. This feature data can be used when comparing face data, but is not sufficient on its own for face recognition. In order to limit external interference, [ISO] also contains specifications for the conditions during image acquisition, such as B. for the positioning of the face and for the lighting conditions. [ISO] is relevant for all applications of facial image recognition in which complete facial image data is exchanged between hardware and software components in open systems via interfaces. It therefore plays an important role for ID cards with the appropriate storage capacity. The standard is relevant for smart cards if they are used as a data storage medium, while the further processing of the facial image data, in particular their comparison, takes place externally. The ICAO prefers the full frontal format as an interoperable face image format for ID cards and travel documents. 6th

7 3.3 Iris Image Data [ISO] defines data formats for iris images. The data records contain a header to identify the data they contain. The actual iris images are pixel-based grayscale images or colored images, possibly compressed according to JPEG or JPEG In order to save storage space, two different image formats are available: Rectilinear: an image with a straight line (data record size kbyte) Polar: a compact image with a round border Data record size approx. 2 KB). When determining the polar images, the boundary of the iris is first determined. Then only the part of the image within this boundary, i.e. the actual iris, is saved. When capturing iris images, much greater precision is required than with facial images, e.g. B. in the correct positioning of the relevant eye and in the lighting conditions. In order to keep incompatibilities of different systems due to disruptive effects during the recording as small as possible, the standard contains not only the actual data formats but also numerous specifications for the execution of the recordings. A standardization of an iris feature data format in addition to the iris image data format is opposed by the fact that the common iris feature data format is patented and is only used in Iridian products. 3.4 Handwritten signatures and identification marks Signature / Sign Time Series Data [ISO] defines a data format for signature time series, i. H. for sequences of chronologically consecutive values, such as those recorded with handwritten signing on graphics tablets or touch-sensitive screens or with special pens and which represent the signature dynamics. The sequences contain values ​​e.g. B. for the x and y coordinates of the pen position, the writing pressure and the pen orientation at the sampling times.The x and y coordinates of the pen position at the sampling times must be contained in every data record according to [ISO]. If the sampling does not take place at approximately constant time intervals, the sampling time must also be specified for each group of measured values. Signature data according to [ISO] are suitable both as intermediate data that are to be exchanged between different biometric components and from which other signature feature data are to be extracted later, as well as feature data, since the time series are directly computer-aided with the help of dynamic time warping algorithms can be compared. However, [ISO] does not yet contain any requirements for preprocessing the data content, e. B. in relation to the displacement, rotation and scaling of the signatures. This makes it difficult to exchange data in heterogeneous systems. Another problem that can affect interoperability is the lack of comparability of values, e.g. B. for writing pressure, which were recorded on different signature recording devices. 7th

8 The signature data format is described in an informative appendix to [ISO] also in ASN.1 (Abstract Syntax Notation 1). The Packed Encoding Rules of ASN.1 are used to encode the data records. [ISO] does not yet contain a compact format that is specially tailored for storage on smart cards. Since signature-on-card matching implementations can use signature time series as feature data [HF04], this would be desirable Signature / Sign Processed Dynamic Data In order to satisfy the desire for a more compact signature dynamic feature data format, the development of [ISO] was started . [ISO] contains a draft format for statistical signature data, which were previously included as optional data elements in [ISO]. However, the compact statistical signature data is not considered sufficient for the recognition of signatures. The national standardization bodies are therefore requested to submit contributions and to propose more suitable signature dynamics characteristic data. 3.5 Vascular Image Data [ISO] defines a generic image format that is intended to enable the interoperable exchange of images of different parts of the body in order to support biometric technologies that work with vascular images. At present, images of fingers, the back of the hand, the palm or the retina are of particular technological importance. This and other image content should be taken into account in the standard so that uniform image properties and recording conditions are ultimately defined for each technology. The current draft defines a suitable recording position and the associated position of the coordinate system for the recording of image data for fingers, back of the hand and palm. For the entire data record, the format provides a header with general information on format, data record length, recording device and number of images in the data record. The head part is followed by one or more vascular image data blocks. Each data block in turn consists of an image header and an (un) compressed vascular image. The picture header contains special information about the following picture, e.g. B. Information on the biometric type (back of the hand, palm, fingers, etc.), the deviation from the standard position, image dimensions, compression and the recording conditions. Additional fields for further vessel recognition technologies are planned. 3.6 Hand Geometry Silhouette Data [ISO] defines a format for feature data obtained from the presentation of the left or right hand. A proven, space-saving coding of outlines in black and white images is used to generate the hand contour feature data. [ISO] provides for two different hand contours: a top view and a side view. An informative appendix explains the use of a support surface with five upwardly protruding pegs, with which the hand and the individual fingers are positioned 8

9 can be. The position of the individual pins is fixed in order to enable reproducible recordings and thus interoperable feature data. The format sees a header among other things. with information about the presented hand, the position of the hand contour, the coding type and the sensor position, followed by the actual contour feature data and optionally manufacturer-specific data. 4 Summary The standardization of exchange formats for biometric data has made progress towards interoperable biometric systems. In order to be able to compare biometric data of the same type, which were recorded and processed with different biometric components, not only the form of the data records but also calculation rules for their content should be standardized. The parts of ISO / IEC 19794 that deal with formats for fingerprint minute data or for fingerprint, face and iris image data have already reached the stage of a Final Draft International Standard and are e.g. Some of them are already used in biometric products. Literature [ANSI00] Data Format for the Interchange of Fingerprint, Facial, & Scar Mark & ​​Tattoo (SMT) Information. American National Standard for Information Systems ANSI / NIST-ITL [DIN66400] Finger Minutiae Encoding Format and Parameters for On-Card Matching. Pre-standard DIN V July 2003 [HF04] O. Henniger, K. Franke: Biometric user authentication on smart cards by means of handwritten signatures. In D. Zhang, A.K. Jain, eds., Proceedings of the 1st International Conference on Biometric Authentication, Hong Kong, China, Springer (Lecture Notes in Computer Science, vol. 3072) [ILO04] ILO Seafarers Identity Documents Biometric Testing Campaign Report Part I. International Labor Organization , Geneva, Technical Report, Revision 2 [ISO] Information technology Common Biometric Exchange Formats Framework Part 1: Data element specification. Final Committee Draft ISO / IEC June 2004 [ISO] Information technology Common Biometric Exchange Formats Framework Part 2: Procedures for the operation of the biometrics registration authority. Final Draft International Standard ISO / IEC FDIS November 2004 [ISO] Information technology Common Biometric Exchange Formats Framework Part 3: Patron format specifications. Working Draft ISO / IEC January 2005 [ISO] Information technology Biometric data interchange formats Part 1: Framework. Final Committee Draft ISO / IEC November 2004 [ISO] Information technology Biometric data interchange formats Part 2: Finger minutiae data. Final Draft International Standard ISO / IEC FDIS January 2005 [ISO] Information technology Biometric data interchange formats Part 3: Finger pattern spectral data. Final Committee Draft ISO / IEC January

10 [ISO] Information technology Biometric data interchange formats Part 4: Finger image data. Final Draft International Standard ISO / IEC FDIS December 2004 [ISO] Information technology Biometric data interchange formats Part 5: Face image data. Final Draft International Standard ISO / IEC FDIS January 2005 [ISO] Information technology Biometric data interchange formats Part 6: Iris image data. Final Draft International Standard ISO / IEC FDIS November 2004 [ISO] Information technology Biometric data interchange formats Part 7: Signature / sign time series data. Committee Draft ISO / IEC January 2005 [ISO] Information technology Biometric data interchange formats Part 8: Finger pattern skeletal data. Committee Draft ISO / IEC January 2005 [ISO] Information technology Biometric data interchange formats Part 9: Vascular image data. Working Draft ISO / IEC January 2005 [ISO] Information technology Biometric data interchange formats Part 10: Hand geometry silhouette data. Working Draft ISO / IEC January 2005 [ISO] Information technology Biometric data interchange formats Part 11: Signature / sign processed dynamic data. Working Draft ISO / IEC January