ISO/IEC 19794-4:2011
(Main)Information technology — Biometric data interchange formats — Part 4: Finger image data
Information technology — Biometric data interchange formats — Part 4: Finger image data
ISO/IEC 19794-4:2011 specifies a data record interchange format for storing, recording, and transmitting the information from one or more finger or palm image areas within an ISO/IEC 19785-1 data structure. This can be used for the exchange and comparison of finger image data. It defines the content, format, and units of measurement for the exchange of finger image data that may be used in the verification or identification process of a subject. The information consists of a variety of mandatory and optional items, including scanning parameters, compressed or uncompressed images and vendor-specific information. This information is intended for interchange among organizations that rely on automated devices and systems for identification or verification purposes based on the information from finger image areas. Information compiled and formatted in accordance with ISO/IEC 19794-4:2011 can be recorded on machine-readable media or may be transmitted by data communication facilities.
Technologies de l'information — Formats d'échange de données biométriques — Partie 4: Données d'image du doigt
General Information
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Standards Content (Sample)
INTERNATIONAL ISO/IEC
STANDARD 19794-4
Second edition
2011-12-15
Information technology — Biometric data
interchange formats —
Part 4:
Finger image data
Technologies de l'information — Formats d'échange de données
biométriques —
Partie 4: Données d'image du doigt
Reference number
ISO/IEC 19794-4:2011(E)
©
ISO/IEC 2011
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ISO/IEC 19794-4:2011(E)
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ISO/IEC 19794-4:2011(E)
Contents Page
Foreword .v
Introduction.vi
1 Scope.1
2 Conformance .1
3 Normative references.2
4 Terms and definitions .2
5 Abbreviated terms .3
6 Data conventions.3
6.1 Byte and bit ordering .3
6.2 Scan sequence .3
7 Image acquisition requirements .3
7.1 General .3
7.2 Pixel aspect ratio .4
7.3 Bit-depth.4
7.4 Grayscale data .4
7.5 Dynamic range.4
7.6 Capture device spatial sampling rate.4
7.7 Image spatial sampling rate .5
7.8 Fingerprint image location .5
7.9 Palm image location.5
8 Finger image record format.5
8.1 Record structure.5
8.2 Finger image general header .6
8.3 Finger/palm image representation header.9
8.4 Extended data .18
9 Registered format type identifiers .23
Annex A (normative) Conformance test methodology .24
Annex B (normative) Capture device certifications .25
Annex C (informative) Finger image data record example .49
Annex D (informative) Conditions for capturing finger image data.51
Annex E (normative) WSQ Gray-scale fingerprint image compression specification.60
Bibliography.91
Figures
Figure 1 — Order of scanned lines .4
Figure 2 — Finger image record structure .6
Figure 3 — Order and size of fields in the finger image record.7
Figure 4 — Image quality layout.13
Figure 5 — Finger orientation for segmentation.22
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ISO/IEC 19794-4:2011(E)
Tables
Table 1 — General record header. 8
Table 2 — Finger image representation header record. 9
Table 3 — Image and extended data . 11
Table 4 — Capture device technology. 12
Table 5 — Identifiers for certification schemes specified in the annexes. 14
Table 6 — Finger position codes . 15
Table 7 — Multiple finger position codes. 15
Table 8 — Palm codes. 16
Table 9 — Compression algorithm codes. 17
Table 10 — Finger and palm impression codes . 18
Table 11 — Extended data area type codes . 19
Table 12 — Segmentation data . 20
Table 13 — Annotation data . 22
Table 14 — Format Type Identifiers . 23
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ISO/IEC 19794-4:2011(E)
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. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75% of the national bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 19794-4 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 19794-4:2005). It reflects the
harmonization across the second generation of ISO/IEC 19794. Clause 8 has been technically revised and
contains descriptions of the harmonized general and representation headers. Annex A is under development
and will contain an amendment for conformance testing methodology for this part of ISO/IEC 19794. Annex B
contains capture device certifications for capturing finger image data. Annex B has been technically revised.
Annex D describes conditions for capturing finger image data, and Annex E contains the WSQ Gray-scale
fingerprint image compression specification. The former Annex A “Image Quality Specification” has been
removed.
ISO/IEC 19794 consists of the following parts, under the general title Information technology — Biometric data
interchange formats:
⎯ Part 1: Framework
⎯ Part 2: Finger minutiae data
⎯ Part 3: Finger pattern spectral data
⎯ Part 4: Finger image data
⎯ Part 5: Face image data
⎯ Part 6: Iris image data
⎯ Part 7: Signature/sign time series data
⎯ Part 8: Finger pattern skeletal data
⎯ Part 9: Vascular image data
⎯ Part 10: Hand geometry silhouette data
⎯ Part 11: Signature/sign processed dynamic data
⎯ Part 13: Voice data
⎯ Part 14: DNA data
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ISO/IEC 19794-4:2011(E)
Introduction
In the forensic community, the capture and transmission of fingerprint images has been a common choice for
the exchange of fingerprint information used by Automatic Fingerprint Identification Systems (AFIS) for the
identification of individuals. However, little to no fingerprint information is being exchanged between
equipment from different vendors in the biometric user verification and access community. This has been due
in part to the lack of agreement between vendors on the amount and type of information to capture, the
method of capture, and the information to be exchanged.
ISO/IEC 19794 is a series of International Standards being developed by ISO/IEC JTC 1/SC 37 that supports
interoperability and data interchange among biometric applications and systems. The series specifies
requirements that solve the complexities of applying biometrics to a wide variety of personal recognition
applications, whether such applications operate in an open systems environment or consist of a single, closed
system. Additional information regarding the series is provided in ISO/IEC 19794-1.
This part of ISO/IEC 19794 is intended for those applications requiring the exchange of raw or processed
fingerprint and palm images that may not necessarily be limited by the amount of resources required for data
storage or transmitting time. It can be used for the exchange of scanned fingerprints containing detailed image
pixel information. This part of ISO/IEC 19794 can also be used to exchange processed fingerprint image data
containing considerably fewer pixels per inch and/or a lesser number of grayscale levels. This is in contrast to
other parts of ISO/IEC 19794 used for exchanging lists of fingerprint characteristics such as minutiae, patterns,
or other variants. These formats require considerably less storage than a fingerprint image. However, by using
any of the other parts of ISO/IEC 19794, information recorded in one standard format cannot be used by
algorithms designed to operate with another type of information. In other words, minutiae data records cannot
be compared with pattern skeletal data comparison subsystems.
Although the minutiae, pattern, or other approaches produce different intermediate outputs, all shall initially
capture a reasonably high quality fingerprint image before reducing the size of the image (in bytes) or
developing a list of characteristic data from the image. Use of the captured or processed image can provide
interoperability among vendors relying on minutiae-based, pattern-based or other algorithms. As a result, data
from the captured finger image offers the developer more freedom in choosing or combining comparison
algorithms. For example, an enrolment image may be stored on a contactless chip located on an identification
document. This will allow future verification of the holder of the document with systems that rely on either
minutiae-based or pattern-based algorithms. Establishment of an image-based representation of fingerprint
information will not rely on pre-established definitions of minutiae, patterns or other types. It will provide
implementers with the flexibility to accommodate images captured from dissimilar devices, varying image
sizes, spatial sampling rates, and different grayscale depths. Use of the fingerprint image will allow each
vendor to implement their own algorithms to determine whether two fingerprint records are from the same
finger.
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INTERNATIONAL STANDARD ISO/IEC 19794-4:2011(E)
Information technology — Biometric data interchange
formats —
Part 4:
Finger image data
1 Scope
This part of ISO/IEC 19794 specifies a data record interchange format for storing, recording, and transmitting
the information from one or more finger or palm image areas. This can be used for the exchange and
comparison of finger image data. It defines the content, format, and units of measurement for the exchange of
finger image data that may be used for enrolment, verification, or identification of a subject. The information
consists of a variety of mandatory and optional items, including scanning parameters, compressed or
uncompressed images and vendor-specific information. This information is intended for interchange among
organizations that rely on automated devices and systems for identification or verification purposes based on
the information from finger image areas. Information compiled and formatted in accordance with this part of
ISO/IEC 19794 can be recorded on machine-readable media or may be transmitted by data communication
facilities.
2 Conformance
A biometric data record conforms to this part of ISO/IEC 19794 if it satisfies all of the normative requirements
related to:
a) its data structure, data values, and the relationships between its data elements, as specified throughout
Clause 8 for the finger image record format of this part of ISO/IEC 19794;
b) the relationship between its data values and the input biometric data from which the biometric data record
was generated, as specified throughout Clause 8 for the finger image record format of this part of
ISO/IEC 19794.
A system that produces biometric data records is conformant to this part of ISO/IEC 19794 if all biometric data
records that it outputs conform to this part of ISO/IEC 19794 (as defined above) as claimed in the
Implementation Conformance Statement (ICS) associated with that system. A system does not need to be
capable of producing biometric data records that cover all possible aspects of this part of ISO/IEC 19794, but
only those that are claimed to be supported by the system in the ICS.
A system that uses biometric data records is conformant to this part of ISO/IEC 19794 if it can read, and use
for the purpose intended by that system, all biometric data records that conform to this part of ISO/IEC 19794
(as defined above) as claimed in the ICS associated with that system. A system does not need to be capable
of using biometric data records that cover all possible aspects of this part of ISO/IEC 19794, but only those
that are claimed to be supported by the system in an ICS.
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ISO/IEC 19794-4:2011(E)
3 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC 10918-1, Information technology — Digital compression and coding of continuous-tone still images:
Requirements and guidelines
ISO/IEC 15444 (all parts), Information technology — JPEG 2000 image coding system
ISO/IEC 15948, Information technology — Computer graphics and image processing — Portable Network
Graphics (PNG): Functional specification
ISO/IEC 19794-1:2011, Information technology — Biometric data interchange formats — Part 1: Framework
ISO/IEC 29794-1, Information technology — Biometric sample quality — Part 1: Framework
4 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 19794-1 and the following apply.
4.1
capture device spatial sampling rate
number of pixels per unit distance used by a sensor or scanning device to initially capture an image
4.2
fingerprint image
area of friction skin on the fleshy surface of a finger located horizontally between the two edges of the
fingernail and vertically between the first joint and the tip of a finger
NOTE It contains a unique pattern of friction ridge and valley information commonly referred to as a “fingerprint”.
4.3
image spatial sampling rate
number of pixels per unit distance in the image
NOTE This may be the result of processing a captured image. The original captured scanned image may have been
subsampled, scaled, down-sampled, or otherwise processed.
4.4
palm
friction ridge skin on the side and underside of the hand
4.5
plain fingerprint image
image captured from a finger placed on a platen without any rolling movement
4.6
rolled fingerprint image
image captured that is located between the two edges of the fingernail
NOTE This type of image is typically acquired using a rolling motion from one edge of the fingernail to the other.
4.7
vertical rolls
fingerprint images that have been captured by rolling a finger vertically from the slap position over the finger
tip to the nail
NOTE This is in contrast to horizontal rolls, which are captured by horizontal rolling from the nail over the slap
position to the other side of the nail as described in the definition for “rolled fingerprint image”.
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ISO/IEC 19794-4:2011(E)
5 Abbreviated terms
For the purposes of this document the following abbreviations and those given in ISO/IEC 19794-1 apply.
ppcm pixels per centimetre
ppi pixels per inch
TIR Total Internal Reflection
6 Data conventions
6.1 Byte and bit ordering
Each item of information, field, or logical record shall contain one or more bytes of data. Within a record all
multibyte quantities are represented in Big-Endian format. That is, the more significant bytes of any multibyte
quantity are stored at lower addresses in memory than less significant bytes. The order for transmission shall
also be the most significant byte first and least significant byte last. Within a byte, the order of transmission
shall be the most significant bit first and the least significant bit last. All numeric values are fixed-length
unsigned integer quantities.
6.2 Scan sequence
It is not the purpose of this part of ISO/IEC 19794 to specify the orientation of the finger (or palm), the method
of scanning, or the order of scanning used to capture the image. However, each image as presented in
accordance with this format standard shall appear to have been captured in an upright position and
approximately centered horizontally in the field of view. The recorded image data shall appear to be the result
of a scanning of an impression of a fingerprint. The scanning sequence (and recorded data) shall appear to
have been captured from left-to-right, progressing from top-to-bottom of the fingerprint or palm print. Figure 1
illustrates the recording order for the scanned image. For the purpose of describing the position of each pixel
within an image to be exchanged, a pair of reference axes shall be used. The origin of the axes, pixel location
(0,0), shall be located at the upper left-hand corner of each image. The x-coordinate (horizontal) position shall
increase positively from the origin to the right side of the image. The y-coordinate (vertical) position shall
increase positively from the origin to the bottom of the image.
7 Image acquisition requirements
7.1 General
Image capture requirements are dependent on various factors including the application, the available amount
of raw pixel information to retain or exchange, and targeted performance metrics. As a result of these factors,
the image capture operation will be associated with a combination of image acquisition parameters settings
described below.
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ISO/IEC 19794-4:2011(E)
Figure 1 — Order of scanned lines
7.2 Pixel aspect ratio
The finger image shall be represented using square pixels, in which the horizontal and vertical dimensions of
the pixels are equal. Any difference between these two dimensions should be within 1%. That is, the ratio of
horizontal to vertical pixel dimensions should be between 0,99 and 1,01.
7.3 Bit-depth
The grayscale precision of the pixel data shall be specified in terms of the bit-depth or the number of bits used
to represent the grayscale value of a pixel. A bit-depth of 3 provides 8 levels of grayscale; a depth of 8
provides 256 levels of gray. For grayscale data, the minimum value that can be assigned to a "black" pixel
shall be zero. The maximum value that can be assigned to a "white" pixel shall be the grayscale value with all
of its bits of precision set to "1". However, the “blackest" pixel in an image may have a value greater than "0"
and the "whitest" pixel may have a value less than its maximum value. For example, the range of values for a
"white" pixel with 5 bits of precision shall be 31 or less. The range of values for a “white” pixel using 8 bits of
precision shall be 255 or less. The bit-depth may range from 1 to 16 bits.
7.4 Grayscale data
Grayscale finger image data shall be stored, recorded, or transmitted in either compressed or uncompressed
form. The image data portion of a record for an uncompressed grayscale image shall contain a set of raw
pixel information. Using a bit-depth of 8 bits (256 grayscale levels) each pixel shall be contained in a single
byte. Pixel values with a depth of less than eight bits shall be stored and transmitted in a packed binary format.
Increased precision for pixel values greater than 255 shall use two unsigned bytes to hold up to sixteen-bit
pixels with values in the range of 0-65535. The encoding of a compressed grayscale image shall be the output
of the appropriate grayscale compression algorithm specified in Table 9. Upon decompression the grayscale
value for each pixel shall be represented in the same manner as pixels in an uncompressed image.
7.5 Dynamic range
The image grayscale shall be encoded using the agreed precision necessary to meet the dynamic range
requirement for a specific application. It is assumed that the precise requirements of the application are known.
7.6 Capture device spatial sampling rate
Grayscale fingerprint images to be captured shall be acquired by an image capture device operating at a
specific scanning spatial sampling rate. As the spatial sampling rate used in the image capture process is
increased, more detailed ridge and structure information for processing becomes available. For minutiae and
small feature based algorithms, use of the higher spatial sampling rate enhances the detection of more closely
spaced features that may not be detected using the minimum spatial sampling rate.
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ISO/IEC 19794-4:2011(E)
7.7 Image spatial sampling rate
The spatial sampling rate of the image data formatted and recorded for interchange may be the scan spatial
sampling rate of the image or it may have been sub-sampled, scaled, down-sampled, or otherwise processed
to produce a form for representing the ridge and valley structure areas of the fingerprint.
7.8 Fingerprint image location
This part of ISO/IEC 19794 is designed to accommodate both plain (flat) or rolled fingerprint images. Biometric
systems perform better if the volar pad of the finger is centered both horizontally and vertically in the image
capture area. Therefore, when capturing a fingerprint image, the center of the fingerprint image should be
located in the approximate center of the image capture area.
For multiple finger verification and/or identification purposes, there are currently fingerprint scanner devices
that will acquire images of multiple fingers during a single capture cycle. These devices are capable of
capturing the plain impressions from two, three, or four adjacent fingers of either hand during a single
scanning. The plain impressions from the two thumbs or two index fingers can also be captured at one time.
Therefore, with three placements of the fingers on a device’s scanning surface all ten fingers from an
individual shall be acquired in three scans – right four fingers, left four fingers, and two thumbs. For these
multi-finger captures, half of the captured fingers should be located to the left of the image center and the
other half of the fingers to the right of the image center.
7.9 Palm image location
This part of ISO/IEC 19794 is also designed to accommodate images from the palm of the hand or from the
side of the hand opposite the thumb also known as the “writer’s palm”. Most comparison subsystems perform
better if the flat or fleshy part of the palm or writer’s palm is centered both horizontally and vertically in the
image capture area. Therefore, when capturing a palmprint image, the center of the palm or writer’s palm
image area should be located in the approximate center of the image capture area. The palm itself may be
captured as one entity, or various pieces of it can be captured as single images such as the thenar (fleshy part
behind the thumb), hyperthenar (fleshy area opposite the thumb), or interdigital (area of the palm directly
beneath the four fingers).
8 Finger image record format
8.1 Record structure
This part of ISO/IEC 19794 defines the composition of the finger image record. Each record shall pertain to a
single subject and shall contain at least one representation for each of one or more fingers, multiple fingers
(single image records), or palms. Figure 2 illustrates the record structure for the finger image record format.
Figure 3 details the order of fields in the record and the length of each field. The fields in white indicate
mandatory fields. Shaded fields indicate optional information.
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ISO/IEC 19794-4:2011(E)
ISO/IEC 19794-4
BDIR
Representation #1 Representation #2 Representation #X
. . .
General Header
(mandatory) (optional) (optional)
Fixed-length
Representation Header
Representation data
Variable-length Variable-length
Figure 2 — Finger image record structure
The organization of the record format is as follows:
• A single fixed-length (16-byte) general record header containing
...
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