ISO/IEC 39794-4:2019

INTERNATIONAL ISO/IEC
STANDARD 39794-4
First edition
2019-12
Information technology — Extensible
biometric data interchange formats —
Part 4:
Finger image data
Reference number
©
ISO/IEC 2019
© ISO/IEC 2019
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ii © ISO/IEC 2019 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 5
5 Conformance . 6
6 Modality specific information . 6
6.1 Capture recommendations . 6
6.1.1 Fingerprint image . 6
6.1.2 Palm image . 6
6.2 Image coordinate system considerations . 7
6.3 Image representation requirements . 7
6.3.1 General. 7
6.3.2 Colorspace . 7
6.3.3 Pixel aspect ratio . 7
6.3.4 Bit-depth . 8
6.3.5 Image spatial sampling rate . 8
7 Abstract data elements . 8
7.1 Purpose and overall structure . 8
7.2 Finger image data block . 9
7.3 Version block . 9
7.4 Representation blocks .10
7.5 Position .10
7.6 Impression .10
7.7 Image data format .11
7.7.1 Supported data format .11
7.7.2 PGM encoding definition .11
7.8 Image data .12
7.9 Capture date/time block . .12
7.10 Capture device block .12
7.10.1 Model identifier block .12
7.10.2 Capture device technology identifier .12
7.10.3 Certification identifier blocks .13
7.11 Quality blocks .14
7.12 Spatial sampling rate block .14
7.13 Position computed by capture device .14
7.14 Original rotation .14
7.15 Image rotated to vertical .14
7.16 Image has been lossily compressed .14
7.17 Segmentation blocks .15
7.18 Annotation blocks .15
7.19 PAD data block.15
7.20 Comment blocks .16
7.21 Vendor specific data blocks .16
8 Encoding .16
8.1 Tagged binary encoding .16
8.2 XML encoding .16
9 Registered BDB format identifiers .16
Annex A (normative) Formal specifications .17
© ISO/IEC 2019 – All rights reserved iii

Annex B (informative) Encoding examples .29
Annex C (normative) Conformance testing methodology .33
Annex D (normative) Capture device certifications .38
Annex E (informative) Conditions for capturing fingerprint image data .62
Annex F (normative) WSQ greyscale finger image compression specification .71
Bibliography .97
iv © ISO/IEC 2019 – All rights reserved

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).
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. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see http:// patents .iec .ch).
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.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 37, Biometrics.
A list of all parts in the ISO/IEC 39794 series can be found on the ISO website.
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.
The purchase of this ISO/IEC document carries a copyright licence for the purchaser to use ISO/IEC
copyright in the schemas in the annexes to this document for the purpose of developing, implementing,
installing and using software based on those schemas, subject to ISO/IEC licensing conditions set out in
the schemas.
© ISO/IEC 2019 – All rights reserved v

Introduction
Biometric data interchange formats enable the interoperability of different biometric systems. The first
generation of biometric data interchange formats has been published between 2005 and 2007 in the
first edition of the ISO/IEC 19794 series. From 2011 onwards, the second generation of biometric data
interchange formats was published in the second edition of the established parts and the first edition
of some new parts of the ISO/IEC 19794 series. In the second generation of biometric data interchange
formats, new useful data elements such as data elements related to biometric sample quality have been
added, the header data structures were harmonized across all parts of the ISO/IEC 19794 series, and
XML encoding has been added in addition to the binary encoding.
In anticipation of the future need for additional data elements and to avoid future compatibility issues,
ISO/IEC JTC 1/SC 37 has developed the ISO/IEC 39794 series as a third generation of biometric data
interchange formats, defining extensible biometric data interchange formats capable of including
future extensions in a defined way. Extensible specifications in ASN.1 (Abstract Syntax Notation One)
and the distinguished encoding rules of ASN.1 form the basis for encoding biometric data in binary
tag-length-value formats. XML schema definitions form the basis for encoding biometric data in XML
(eXtensible Markup Language).
This third generation of finger image data interchange formats complements ISO/IEC 19794-4 (both
the 2005 and 2011 editions). The first generation of biometric data interchange formats, which has been
adopted, e.g. by ICAO for the biometric data stored in machine readable travel documents, is expected
to be retained in the standards catalogue as long as needed.
This document is intended for those applications requiring the exchange of raw or processed fingerprint
and other friction ridge images (for example, palm images) that may not necessarily be limited in the
amount of resources available for data storage or transmitting time. It can be used for the exchange of
scanned fingerprints containing detailed image pixel information.
Use of the captured or processed image allows interoperability among biometric systems relying on
minutiae-based, pattern-based or other algorithms. Thus, 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 greyscale depths. Use of the finger image will allow each vendor to
implement their own algorithms to determine whether two fingerprint records are from the same finger.
This document supports both binary and XML encoding, to support a spectrum of user requirements.
With XML, this document meets the requirements of modern IT architectures. With binary encoding
this document is also able to be used in bandwidth or storage constrained environments.
vi © ISO/IEC 2019 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 39794-4:2019(E)
Information technology — Extensible biometric data
interchange formats —
Part 4:
Finger image data
1 Scope
This document specifies:
— generic extensible data interchange formats for the representation of friction ridge image data: a
tagged binary data format based on an extensible specification in ASN.1 and a textual data format
based on an XML schema definition that are both capable of holding the same information;
— examples of data record contents;
— application specific requirements, recommendations, and best practices in data acquisition; and
— conformance test assertions and conformance test procedures applicable to this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 2382-37, Information technology — Vocabulary — Part 37: Biometrics
ISO/IEC 8824-1, Information technology — Abstract Syntax Notation One (ASN.1): Specification of basic
notation — Part 1
ISO/IEC 8825-1, Information technology — ASN.1 encoding rules — Part 1: Specification of Basic Encoding
Rules (BER), Canonical Encoding Rules (CER), and Distinguished Encoding Rules (DER)
ISO/IEC 14495-1, Information technology — Lossless and near-lossless compression of continuous-tone still
images: Baseline
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 39794-1, Information technology — Extensible biometric data interchange formats — Part 1:
Framework
W3C Recommendation, XML Schema Part 1: Structures (Second Edition), 28 October 2004
W3C Recommendation, XML Schema Part 2: Datatypes (Second Edition), 28 October 2004
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 2382-37, ISO/IEC 39794-1
and the following apply.
© ISO/IEC 2019 – All rights reserved 1

ISO and IEC maintain terminological databases for use in standardisation at the following addresses:
— IEC Electropedia available at http:// www .electropedia .org/
— ISO Online Browsing Platform available at http:// www .iso .org/ obp.
3.1
spatial sampling rate
number of pixels per unit distance used by a sensor or scanning device to initially capture an image
3.2
coding model
procedure used to convert input data into symbols to be coded
3.3
coding process
general term for referring to an encoding process, a decoding process, or both
3.4
column
samples per line in an image
3.5
compressed data
either compressed image data or table specification data or both
3.6
compressed image data
coded representation of an image
Note 1 to entry: As specified in Annex F.
3.7
compression
reduction in the number of bits used to represent source image data
3.8
decoder
embodiment of a decoding process
3.9
decoding process
process which takes as its input compressed image data and outputs a continuous-tone image
3.10
dequantization
inverse procedure to quantization by which the decoder recovers a representation of the DWT
coefficients
3.11
reconstructed image
continuous-tone image which is the output of the decoder
Note 1 to entry: As defined in Annex F.
3.12
source image
continuous-tone image used as input to any encoder
Note 1 to entry: As defined in Annex F.
2 © ISO/IEC 2019 – All rights reserved

3.13
digital image
two-dimensional array of data
3.14
downsampling
procedure by which the spatial resolution of an image is reduced
3.15
DWT
discrete wavelet transform
linear transformation, implemented by a multirate filter bank, that maps a digital input signal to a
collection of output subbands
3.16
encoder
embodiment of an encoding process
3.17
encoding process
process which takes as its input a continuous-tone image and outputs compressed image data
3.18
entropy-coded data segment
independently decodable sequence of entropy encoded bytes of compressed image data
3.19
entropy decoder
embodiment of an entropy decoding procedure
3.20
entropy decoding
lossless procedure which recovers the sequence of symbols from the sequence of bits produced by the
entropy coder
3.21
entropy encoder
embodiment of an entropy encoding procedure
3.22
entropy encoding
lossless procedure which converts a sequence of input symbols into a sequence of bits such that the
average number of bits per symbol approaches the entropy of the input symbols
3.23
fingerprint image
representation of an 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 1 to entry: It contains a unique pattern of friction ridge and valley information commonly referred to as a
“fingerprint”.
3.24
Huffman decoder
embodiment of a Huffman decoding procedure
3.25
Huffman decoding
entropy decoding procedure which recovers the symbol from each variable length code produced by
the Huffman encoder
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3.26
Huffman encoder
embodiment of a Huffman encoding procedure
3.27
Huffman encoding
entropy encoding procedure which assigns a variable length code to each input symbol
3.28
Huffman table
set of variable length codes required in a Huffman encoder and Huffman decoder
3.29
image data
either source image data or reconstructed image data
3.30
image spatial sampling rate
number of pixels per unit distance in the image
Note 1 to entry: This may be the result of processing a captured image. The original captured scanned image may
have been subsampled, scaled, downsampled, or otherwise processed.
3.31
interchange format
representation of compressed image data for exchange between application environments
3.32
lossless
descriptive term for encoding and decoding processes and procedures in which the output of the
decoding procedure(s) is identical to the input to the encoding procedure(s)
3.33
marker
two-byte code in which the first byte is FF and the second byte is a value between 1 and FE
Hex Hex
3.34
marker segment
marker and associated set of parameters
3.35
palm
friction ridge skin on the side and underside of the hand
3.36
parameter
fixed length integers 8, 16, or 32 bits in length, used in the compressed data format
3.37
plain fingerprint image
image captured from a finger placed on a platen without any rolling movement
3.38
procedure
set of steps which accomplishes one of the tasks which comprise an encoding or decoding process
3.39
progressive
separation of data segments into blocks that can be transmitted successively to allow the
compressed image data to be decoded at successively higher levels of resolution
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3.40
quantization table
set of quantization values (i.e., bin widths) used to quantize DWT coefficients within the subbands
3.41
quantize
act of performing the quantization procedure for a DWT coefficient
3.42
restart interval
number of coefficients processed as an independent sequence within an image
3.43
restart marker
marker that separates two restart intervals in an image
3.44
rolled fingerprint image
image captured that is located between the two edges of the fingernail
Note 1 to entry: This type of image is typically acquired using a rolling motion from one edge of the fingernail to
the other.
3.45
run length
number of consecutive symbols of the same value
3.46
SWT
symmetric wavelet transform
linear transform implemented by applying a DWT to a periodized symmetric extension of the input signal
3.47
sample
one element in the two-dimensional array which comprises a finger image
3.48
table specification data
coded representation from which the tables, used in the encoder and decoder, are generated
3.49
upsampling
procedure by which the spatial resolution of an image is increased
4 Abbreviated terms
For the purposes of this document, the abbreviated terms given in ISO/IEC 39794-1 and the
following apply.
ppcm pixels per centimetre
ppi pixels per inch
CTF contrast transfer function
JPEG joint photographic experts group
MTF modulation transfer function
PGM portable gray map
© ISO/IEC 2019 – All rights reserved 5

PNG portable network graphics
TIR total internal reflection
WSQ wavelet scalar quantization
5 Conformance
A biometric data block (BDB) conforms to this document if it satisfies all of the requirements related to:
— its data structure, data values and the relationships between its data elements as specified
throughout Clauses 6, 7, 8, and Annex A, and
— the relationship between its data values and the input biometric data from which the biometric data
record was generated as specified throughout Clauses 6, 7, 8, and Annex A.
A system that produces biometric data records conforms to this document if all biometric data
records that it outputs conform to this document (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 document, but only those that
are claimed to be supported by the system in the ICS.
A system that uses biometric data records conforms to this document if it can read, and use for the
purpose intended by that system, all biometric data records that conform to this document (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 document, but only those that are claimed
to be supported by the system in an ICS.
6 Modality specific information
6.1 Capture recommendations
6.1.1 Fingerprint image
This document is designed to accommodate both plain (flat) or rolled fingerprint images. Biometric
systems perform better if the volar pad of the finger is centred both horizontally and vertically in the
image capture area. Therefore, when capturing a fingerprint image, the centre of the fingerprint image
should be located in the approximate centre of the image capture area.
For multiple finger verification and/or identification purposes, there exist fingerprint capture 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 would 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
centre and the other half of the fingers to the right of the image centre.
6.1.2 Palm image
This document 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 centred both horizontally and vertically in
the image capture area. Therefore, when capturing a palmprint image, the centre of the palm or writer’s
palm image area should be located in the approximate centre 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
6 © ISO/IEC 2019 – All rights reserved

thenar (fleshy part behind the thumb), hypothenar (fleshy area opposite the thumb), or interdigital
(area of the palm directly beneath the four fingers).
6.2 Image coordinate system considerations
The recorded image data shall appear to be the result of a scanning of an impression of a friction ridge
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.
To assure that friction ridge images are interoperable with existing fingerprint images in legacy
datasets, care shall be taken to assure that the orientation of the fingerprint is correct. Figure 1 shows
how this shall be achieved.
Figure 1 — Illustration of fingerprint orientation
6.3 Image representation requirements
6.3.1 General
Image representation requirements are dependent on various factors including the application, the
available amount of raw pixel information to retain or exchange, and targeted performance metrics.
Because of these factors, the images represented will have characteristics based on the aspects
described in 6.3.2 through 6.3.5.
6.3.2 Colorspace
Finger images shall be represented as greyscale image data.
6.3.3 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 %,
i.e. the ratio of horizontal to vertical pixel dimensions should be between 0,99 and 1,01.
© ISO/IEC 2019 – All rights reserved 7

6.3.4 Bit-depth
The greyscale precision of the pixel data shall be specified in terms of the bit-depth or the number of
bits used to represent the greyscale value of a pixel. A bit-depth of 8 provides 256 levels of grey. For
greyscale 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 greyscale 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.
6.3.5 Image spatial sampling rate
The spatial sampling rate of the image data formatted and recorded for interchange establishes the
number of pixels for a given distance over the fingerprint object. A finger image may be represented
with a certain number of pixels per cm (ppcm) or pixels per inch (ppi). A finger image with a sampling
rate of 197 ppcm is practically equivalent to a finger image with a sampling rate of 500 ppi. For example,
if a spatial sampling rate of 500 ppi is established for a fingerprint sensor with a width of 0.635 cm
(corresponding to a quarter inch), there will be 125 pixels across the width of the image.
7 Abstract data elements
7.1 Purpose and overall structure
This clause describes the contents of data elements defined in this document. The description is
independent of the encoding of the data elements.
The full naming conventions for ASN.1 module components and component types definitions, naming
conventions for XML schema elements and element types definitions also ASN.1 and XML schema
definition extensions applied per the ISO/IEC 39794 series are specified in ISO/IEC 39794-1.
The tagged binary encoding as well as the XML encoding is given in Clause 8 and Annex A.
The structure of the abstract data elements is described in Figure 2.
8 © ISO/IEC 2019 – All rights reserved

Figure 2 — Fingerprint image data block
NOTE Figure 2 is not automatically generated and can only be viewed as an overview of the structure.
7.2 Finger image data block
Abstract values: See Figure 2 – Fingerprint image data block.
Contents: This data element is the container for all the data associated with the finger image.
7.3 Version block
Abstract values: See ISO/IEC 39794-1.
Contents: The generation number of this document shall be 3. The year shall be the year of the
publication of this document.
© ISO/IEC 2019 – All rights reserved 9

7.4 Representation blocks
Abstract values: See Figure 2 – Fingerprint image data block.
Contents: This data element is the container for all the data associated with the finger image,
except for the version block information.
7.5 Position
Abstract values: See Annex A. As the number of positions is long and duplicative, it is best to under-
stand the possible positions by examining the schema directly.
Contents: This data element establishes which friction ridge region is encoded in the image
data. For example, a right index finger image is described with a position of “right-
IndexFinger” in an ASN.1 encoding. Note that the position encodings are specified
to improve interoperability with existing standards, notably ANSI/NIST ITL stand-
[3]
ards .
7.6 Impression
Abstract values: See Table 1.
Contents: This data element establishes how the friction ridge interacted with the capture
system at the time of capture. Note that the impression encodings are specified to
improve interoperability with existing standards, notably ANSI/NIST ITL stand-
[3]
ards .
Table 1 — Description for finger impression values
Abstract value Description
plainContact A stationary subject’s friction ridge in contact with a fixed scanning sur-
face (or platen).
rolledContact A laterally rolled subject’s friction ridge in contact with a fixed scanning
surface (or platen).
latentImage A residue from a subject’s friction ridge left on a surface that has been
captured.
swipeContact A moving subject’s friction ridge (typically vertically) in contact with a
fixed thin scanning bar.
stationarySubjectContactlessPlain A subject’s friction ridge captured without contact in such a way that the
image is not representative of a roll or other 3D structure, and in which
the subject is expected to remain mostly motionless.
stationarySubjectContactlessRolled A subject’s friction ridge captured without contact in such a way that the
image is representative of a roll or other 3D structure, and in which the
subject is expected to remain mostly motionless. A multi-camera system
that captures many views of a fingerprint and stitches them together to
create a rolled image would fall into this category.
movingSubjectContactlessPlain A subject’s friction ridge captured without contact in such a way that the
image is not representative of a roll or other 3D structure, and in which
the subject is expected to move to perform an effective capture. A con-
tactless “swipe” sensor in which the subject slides their fingers above a
capture system would fall into this category.
movingSubjectContactlessRolled A subject’s friction ridge captured without contact in such a way that the
image is representative of a roll or other 3D structure, and in which the
subject is expected to move to perform an effective capture. A system in
which a subject performs a rolling action above or inside a capture sys-
tem (without platen contact) would fall into this category.
10 © ISO/IEC 2019 – All rights reserved

Table 1 (continued)
Abstract value Description
unknownImpression Impression information was not captured or has been lost.
otherImpression Impression information is known, but does not correspond to any speci-
fied values.
7.7 Image data format
7.7.1 Supported data format
Abstract values: See Table 2.
Contents: Finger images shall be encoded using uncompressed or compressed formats. The
format used to encode the finger image data shall match the format specified in this
data element. Table 2 lists the supported data formats and associated parameters
that may be used.
Table 2 — Image data format
Abstract Image data for- Normative Allowed spatial Maximum
value mat reference sampling compression ratio
pgm None None All None
wsq WSQ IAFIS_IC-0110, 197 ppcm 15:1
Annex F
Jpeg2000Lossy JPEG 2000 ISO/IEC 15444 394 ppcm 15:1
(lossy)
Jpeg2000Lossless JPEG 2000 ISO/IEC 14495-1 197 ppcm or None
(lossless) 394 ppcm
png PNG ISO/IEC 15948 All None
7.7.2 PGM encoding definition
A finger image may be encoded in the Netpbm portable grayscale binary image format. The format
[15]
definition is :
1) a "magic number" = “P5” for identifying the file type followed by:
2) any whitespace (blanks, TABs, CRs, LFs);
3) a width formatted as ASCII characters in decimal;
4) any whitespace (blanks, TABs, CRs, LFs);
5) a height in ASCII decimal;
6) any whitespace (blanks, TABs, CRs, LFs);
7) the maximum grayscale value (Maxval), again in ASCII decimal: the Maxval shall be less than
65536, and more than zero;
8) a single whitespace character (usually a newline);
9) a raster of height rows, in order from top to bottom. Each row consists of width grayscale values, in
order from left to right. Each grayscale value is a number from 0 through Maxval, with 0 being black
and Maxval being white. Each grayscale value is represented in pure binary by either 1 or 2 bytes. If
the Maxval is less than 256, it is 1 byte. Otherwise, it is 2 bytes. The most significant byte is first.
© ISO/IEC 2019 – All rights reserved 11

7.8 Image data
Contents: This data element contains the encoded friction ridge image data.
NOTE The finger image data does not necessarily represent a finger. In general, any position specified in 7.5
may be collected and would be encoded into the finger image data element.
7.9 Capture date/time block
See ISO/IEC 39794-1.
7.10 Capture device block
7.10.1 Model identifier block
See ISO/IEC 39794-1.
7.10.2 Capture device technology identifier
Abstract Values: See Table 3.
Contents: This data element establishes the class of capture device technology used to
acquire the captured biometric sample. Note that the technology encodings are
specified to improve interoperability with existing standards, notably ANSI/NIST
[3]
ITL standards .
Table 3 — Description for finger image capture device technology identifier
Abstract value Description
unknownTechnology Capture device technology information was not captured or has been lost.
otherTechnology Capture device technology information is known, but does not correspond
to any specified values.
scannedInkOnPaper Subjects ink their fingerprints and apply them to paper (cardstock) which
can then be imaged/scanned.
NOTE  Card scanners would encode their technology type as scanned-
InkOnPaper.
opticalTIRBrightField Contact prism such that ridges absorb light from the illumination system.
opticalTIRDarkField Contact prism such that ridges reflect light from the illumination system.
opticalImage Differences in the ridge detail are captured by an optical capture system.
opticalLowFrequency3DMapped A 3D model of the shape of the finger is used to project reflected light from
ridges onto a flattened (2D) model of the finger.
opticalHighFrequency3DMapped A 3D model that is sensitive to the 3D distances between ridges and valleys
is used to project reflected light from ridges onto a flattened (2D) model of
the finger.
capacitive A contact sensor that utilizes the difference in charge between touch-
ing ridges and non-touching valleys. The sensor acts as one plate of the
capacitor, the non-conducting epidermis as a dielectric, and the conduct-
ing dermis as the other plate. There are active and passive versions of the
technology.
capacitiveRF A low radio frequency (RF) signal is applied to the ridge detail and reflec-
tions are sensed by the detector array, with each pixel operating like a tiny
antenna.
electroLuminescence A contact technology in which the ridges and an alternating current (AC) sig-
nal cause an EL panel to emit light which is captured by an imaging system.
12 © ISO/IEC 2019 – All rights reserved

Table 3 (continued)
Abstract value Description
reflectedUltrasonic High frequency sound signals are applied to the ridge detail and the acous-
tic response is sensed by the detector array, with each pixel operating like a
tiny microphone.
impediographicUltrasonic A contact technology in which the absorption of ultrasonic energy is meas-
ured by changes in the impedance of a piezo-electric material.
thermal Thermal differences between contact ridges and ambient temperature in
valleys are used by a detector array, with each pixel operating like a tiny
thermometer.
directPressure These sensors operate by measuring the pressure difference between
ridges and valleys, as the valleys are not involved in any direct force on
the surface of the sensor. The pressure is measured by a detector array,
with each pixel operating like a tiny scale. In practice, these sensors are
electronic binary switches that use time and/or spatial diversity to achieve
grayscale detail.
indirectPressure A contact technology in which the pressure of the fingerprint ridge skin
against a deformable material is assessed optically to produce a friction
ridge image.
liveTape A technology in which one-time use tape is used on live friction ridge skin
to collect friction ridge detail and the tape is then subsequently imaged by
traditional photography.
latentImpression A powder is applied to a surface that a fingerprint has touched. The oil
residue of the finger attaches to the powder. This is then photographed and
post-processed to produce a latent finger image.
latentPhoto A printed photograph of a latent impression is subsequently imaged (with a
scanner or camer
...