ISO/IEC 19794-7:2014

INTERNATIONAL ISO/IEC
STANDARD 19794-7
Second edition
2014-02-01
Information technology — Biometric
data interchange formats —
Part 7:
Signature/sign time series data
Technologies de l’information — Formats d’échange de données
biométriques —
Partie 7: Données de série chronologique de signature/signe
Reference number
©
ISO/IEC 2014
© ISO/IEC 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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ii © ISO/IEC 2014 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Conformance . 1
3 Normative references . 2
4 Terms and definitions . 2
5 Abbreviated terms . 4
6 Conventions . 4
6.1 Coordinate system . 4
6.2 Octet and bit order . 4
6.3 Registered format type identifiers . 4
7 Channels . 5
7.1 General . 5
7.2 Pen tip position channels: X, Y, Z . 6
7.3 Pen tip velocity channels: VX, VY . 6
7.4 Pen tip acceleration channels: AX, AY . 6
7.5 Time channel: T . 6
7.6 Time difference channel: DT . 6
7.7 Pen tip force channel: F . 6
7.8 Pen tip switch state channel: S . 7
7.9 Pen orientation channels: TX, TY, A, E, R . 7
8 Full format . 8
8.1 Record organisation . 8
8.2 General header . 9
8.3 Record body .10
9 Compact format .16
9.1 Record organisation .16
9.2 Comparison algorithm parameters template .17
9.3 Embedment in a CBEFF data structure .18
9.4 Record body .19
10 Compression format .19
10.1 Record organisation .19
10.2 General header .20
10.3 Record body .20
Annex A (normative) Conformance testing methodology .23
Annex B (informative) Best practices .
Data acquisition.71
Annex C (informative) ASN.1 specification of the compact format
....................................................................................72
Annex D (informative) Signature/sign coding examples .75
Bibliography .77
© ISO/IEC 2014 – 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. 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 19794-7 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 37, Biometrics.
This second edition revises the first edition (ISO/IEC 19794-7:2007). Clauses 7 and 8 have been
technically revised and it has been amended by Clause 10 and Annex A. It also incorporates the Technical
Corrigendum ISO/IEC 19794-7:2007/Cor.1:2009.
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 14: DNA data
The following part is under preparation:
— Part 13:Voice data
iv © ISO/IEC 2014 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 19794-7:2014(E)
Information technology — Biometric data interchange
formats —
Part 7:
Signature/sign time series data
1 Scope
This part of ISO/IEC 19794 specifies data interchange formats for signature/sign behavioural data
captured in the form of a multi-dimensional time series using devices such as digitizing tablets or
advanced pen systems. The data interchange formats are generic, in that they may be applied and used
in a wide range of application areas where handwritten signs or signatures are involved. No application-
specific requirements or features are addressed in this part of ISO/IEC 19794.
This part of ISO/IEC 19794 contains
— a description of what data may be captured,
— three data formats for containing the data: a full format for general use, a compression format capable
of holding the same amount of information as the full format but in compressed form, and a compact
format for use with smart cards and other tokens that does not require compression/decompression
but conveys less information than the full format, and
— examples of data record contents and best practices in capture.
Specifying which of the format types and which options defined in this part of ISO/IEC 19794 are to
be applied in a particular application is out of scope; this needs to be defined in application-specific
requirements specifications or application profiles.
It is advisable that cryptographic techniques be used to protect the authenticity, integrity, and
confidentiality of stored and transmitted biometric data; yet such provisions are beyond the scope of
this part of ISO/IEC 19794.
This part of ISO/IEC 19794 also specifies elements of conformance testing methodology, test assertions,
and test procedures as applicable to this part of ISO/IEC 19794. It establishes test assertions on the
structure and internal consistency of the signature/sign time series data formats defined in this part
of ISO/IEC 19794 (type A level 1 and 2 as defined in ISO/IEC 19794-1:2011/Amd.1), and semantic test
assertions (type A level 3 as defined in ISO/IEC 19794-1:2011/Amd.1).
The conformance testing methodology specified in this part of ISO/IEC 19794 does not establish:
— tests of other characteristics of biometric products or other types of testing of biometric products
(e.g. acceptance, performance, robustness, security),
— tests of conformance of systems that do not produce data records claimed to conform to the
requirements of this part of ISO/IEC 19794.
2 Conformance
A biometric data record conforms to this part of ISO/IEC 19794 if it satisfies the format requirements with
respect to its structure, with respect to relations among its fields, and with respect to relations between
its fields and the underlying input that are specified within clauses 6–10 of this part of ISO/IEC 19794.
© ISO/IEC 2014 – All rights reserved 1

Biometric data interchange format conformance tests conform to this part of ISO/IEC 19794 if they
satisfy all of the normative requirements set forth in Annex A. Specifically, all level-1, level-2, and level-3
tests shall use the test assertions defined in Table A.2, Table A.3, and Table A.4 of clause A.2 in conformity
with the concept and rules set in ISO/IEC 19794-1:2011/Amd.1.
Implementations of this part of ISO/IEC 19794 tested according to the specified methodology shall be
able to claim conformance only to those biometric data record requirements specified in this part of
ISO/IEC 19794 that are tested by the test methods established by this methodology.
Implementations of this part of ISO/IEC 19794 do not necessarily need to conform to all possible aspects
of this part of ISO/IEC 19794, but only to those requirements that are claimed to be supported by the
implementation in an implementation conformance statement (ICS), filled out in accordance with
ISO/IEC 19794-1:2011/Amd.1 and Table A.1 of clause A.1 of this part of ISO/IEC 19794.
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 8825-1, Information technology — ASN.1 encoding rules: Specification of Basic Encoding Rules
(BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) — Part 1
ISO/IEC 19785-1, Information technology — Common Biometric Exchange Formats Framework — Part 1:
Data element specification
ISO/IEC 19785-2, Information technology — Common Biometric Exchange Formats Framework — Part 2:
Procedures for the operation of the Biometric Registration Authority
ISO/IEC 19785-3, Information technology — Common Biometric Exchange Formats Framework — Part 3:
Patron format specifications
ISO/IEC 19794-1:2011, Information technology — Biometric data interchange formats — Part 1: Framework
4 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 19794-1:2011 and the
following apply.
4.1
channel
data item (captured, intermediate, or processed) recorded in form of a time series
EXAMPLE pen tip position x and y coordinates, pen tip force, pen tilt along the x and y axes, pen azimuth, pen
elevation, pen rotation
4.2
compression
process that reduces the size of a digital file with or without loss of information
Note 1 to entry: The compression format defined in clause 10 includes data compressed by lossless compression
schemes.
4.3
pen azimuth
angle measured clockwise from the positive y axis to the perpendicular projection of the pen onto the
writing plane
Note 1 to entry: The pen azimuth may range from 0° to 360°.
2 © ISO/IEC 2014 – All rights reserved

4.4
pen-down event
event from which on the pen tip is touching the writing plane
4.5
pen elevation
angle between the perpendicular projection of the pen onto the writing plane and the pen
Note 1 to entry: The pen elevation may range from 0° to 90°.
4.6
pen rotation
angle of the rotation of the pen about its longitudinal axis measured counter-clockwise from a device-
specific rotational reference position
Note 1 to entry: The pen rotation may range from 0° to 360°.
4.7
pen tilt along the x axis
angle measured clockwise from the positive z axis to the perpendicular projection of the pen onto the
x,z plane
Note 1 to entry: The pen tilt along the x axis may range from –90° to +90°.
4.8
pen tilt along the y axis
angle measured clockwise from the positive z axis to the perpendicular projection of the pen onto the
y,z plane
Note 1 to entry: The pen tilt along the y axis may range from –90° to +90°.
4.9
pen-up event
event from which on the pen tip is not touching the writing plane, after a pen-down event
4.10
sampling rate
number of samples per second (or per other unit) taken from a continuous signal to make a discrete
signal
4.11
signature/sign representation
data recorded from a single signature/sign
4.12
X jitter
sample standard deviation of at least 100 x coordinate samples from a stationary pen
4.13
Y jitter
sample standard deviation of at least 100 y coordinate samples from a stationary pen
4.14
X pixel density
number of dots per millimetre that the capture device resolves in the x (horizontal) direction
4.15
Y pixel density
number of dots per millimetre that the capture device resolves in the y (vertical) direction
© ISO/IEC 2014 – All rights reserved 3

5 Abbreviated terms
lsb least significant bit
msb most significant bit
6 Conventions
6.1 Coordinate system
The coordinate system used to express the pen position shall be a three-dimensional Cartesian coordinate
system. The x axis shall be the horizontal axis of the writing plane, with x coordinates increasing to the
right. The y axis shall be the vertical axis of the writing plane, with y coordinates increasing upwards.
The z axis shall be the axis perpendicular to the writing plane, with z coordinates increasing upwards
out of the writing plane starting from 0. For an illustration see Figure 1.
z
y
Writing plane
x
Figure 1 — Coordinate system
NOTE The origin of x and y coordinates is not specified here. Depending on the used technology, it may be, for
instance, in the centre of the writing pad, at its lower left corner, or at the pen position at the first pen-down event.
6.2 Octet and bit order
The more significant bytes of any multi-byte quantity are stored at lower addresses in memory than
(and are transmitted before) less significant bytes.
Within a byte, the bits are numbered from 8 to 1, where bit 8 is the ‘most significant bit’ (msb) and bit 1
the ‘least significant bit’ (lsb).
6.3 Registered format type identifiers
The data records specified in this part of ISO/IEC 19794 may be embedded in a CBEFF- (ISO/IEC 19785-
1) compliant biometric information record (BIR). This clause lists the BDB (biometric data block) format
owner identifier and the BDB format type identifiers that shall be used if embedded in a CBEFF BIR.
These identifiers are registered with IBIA, the CBEFF Registration Authority (see ISO/IEC 19785-2).
The format owner of the formats defined in ISO/IEC 19794 is ISO/IEC JTC 1/SC 37. The format owner
identifier is 257 (0101 ). Table 1 lists the format type identifiers for the formats defined in this part
Hex
of ISO/IEC 19794.
4 © ISO/IEC 2014 – All rights reserved

Table 1 — Format type identifiers
CBEFF BDB format Short name Full object identifier
type identifier
14 (000e ) signature-sign-time- {iso(1) registration-authority(1) cbeff(19785) biometric-organization(0)
Hex
series-full jtc1-sc37(257) bdbs(0) signature-sign-time-series-full(14)}
15 (000f ) signature-sign-time- {iso(1) registration-authority(1) cbeff(19785) biometric-organization(0)
Hex
series-compact jtc1-sc37(257) bdbs(0) signature-sign-time-series-compact(15)}
30 (001e ) signature-sign-time- {iso(1) registration-authority(1) cbeff(19785) biometric-organization(0)
Hex
series-compression jtc1-sc37(257) bdbs(0) signature-sign-time-series-compression(30)}
NOTE 1 The format type identifier for the full format defined in this edition of ISO/IEC 19794-7 is the same
as the one for the full format defined in ISO/IEC 19794-7:2007. An indication of which version of the full format
applies can be determined from the version number included in the general header.
NOTE 2 The compact format defined in this edition of ISO/IEC 19794-7 is the same as the one defined in
ISO/IEC 19794-7:2007. Hence, the format type identifier for the compact format defined in this edition of
ISO/IEC 19794-7 is also the same as the one for the compact format defined in ISO/IEC 19794-7:2007.
7 Channels
7.1 General
Table 2 lists the channel names and their meanings. Signature/sign time series data captured with
different capture devices or used in different applications may contain data from different channels.
Either the T channel or the DT channel shall be present, or uniform sampling (constant time difference
between adjacent sample points) shall be indicated (see clause 7.6). Inclusion of at least one other channel
is mandatory.
Table 2 — Channels
Channel Description
name
X x coordinate (horizontal pen position)
Y y coordinate (vertical pen position)
Z z coordinate (height of pen above the writing plane)
VX velocity in x direction
VY velocity in y direction
AX acceleration in x direction
AY acceleration in y direction
T time
DT time difference
F pen tip force
S pen tip switch state (touching/not touching the writing plane)
TX pen tilt along the x axis
TY pen tilt along the y axis
A pen azimuth
E pen elevation
R pen rotation
© ISO/IEC 2014 – All rights reserved 5

7.2 Pen tip position channels: X, Y, Z
There are three channels defined for recording pen tip position data in the three-dimensional space.
The X channel is for recording the x coordinate of the projection of the pen tip on the writing plane. The
Y channel is for recording the y coordinate of the projection of the pen tip on the writing plane. The Z
channel is for recording the height of the pen tip above the writing plane.
The unit of measurement is millimetres (mm). To restore the actual values, the integer values given
in the record body are to be divided by a scaling value given in the channel description. By choosing
appropriate scaling values, different degrees of accuracy can be expressed.
7.3 Pen tip velocity channels: VX, VY
The VX channel is for recording the pen tip velocity along the x axis. The VY channel is for recording the
pen tip velocity along the y axis.
The unit of measurement is millimetres per second (mm/s). To restore the actual values, the integer
values given in the record body are to be divided by a scaling value given in the channel description. By
choosing appropriate scaling values, different degrees of accuracy can be expressed.
7.4 Pen tip acceleration channels: AX, AY
The AX channel is for recording the pen tip acceleration along the x axis. The AY channel is for recording
the pen tip acceleration along the y axis.
The unit of measurement is millimetres per square second (mm/s ). To restore the actual values,
the integer values given in the record body are to be divided by a scaling value given in the channel
description. By choosing appropriate scaling values, different degrees of accuracy can be expressed.
7.5 Time channel: T
The T channel is for recording the time elapsed since the first sample.
The unit of measurement is seconds (s). To restore the actual values, the integer values given in the
record body are to be divided by a scaling value given in the channel description. By choosing appropriate
scaling values, different degrees of accuracy can be expressed.
7.6 Time difference channel: DT
The DT channel is for recording the time elapsed since the previous sample point.
The unit of measurement is seconds (s). To restore the actual values, the integer values given in the
record body are to be divided by a scaling value given in the channel description. By choosing appropriate
scaling values, different degrees of accuracy can be expressed.
In case of uniform sampling, the channel inclusion field (see clause 8.3.2.8.1) in the representation
header should indicate the DT channel as present, but the DT channel values should be absent in the
representation body while the channel description preamble (see clause 8.3.2.8.2) for the DT channel
indicates the time differences between adjacent sample points as constant.
7.7 Pen tip force channel: F
The F channel is for recording the magnitude of the pen tip force.
6 © ISO/IEC 2014 – All rights reserved

The unit of measurement is Newton (N). To restore the actual values, the integer values given in the
record body are to be divided by a scaling value given in the channel description. By choosing appropriate
scaling values, different degrees of accuracy can be expressed.
NOTE The direction of the pen-tip force depends on the capture device technology, which is identified by the
capture device technology identifier.
7.8 Pen tip switch state channel: S
The S channel is for recording whether the pen tip touches the writing plane or not. The value shall be 0
in case that the pen tip does not touch the writing plane. In case of pen-down events, the value shall also
be 0. The value shall be 1 in case that the pen tip touches the writing plane. In case of pen-up events, the
value shall also be 1.
NOTE Temporarily maintaining a value of 0 when the pen tip starts touching the writing plane allows a
recognition of pen-down events even if the capture device provides no sample points for pen-up strokes.
7.9 Pen orientation channels: TX, TY, A, E, R
There are five channels defined for recording pen orientation data. The A channel is for recording the
pen azimuth. The E channel is for recording the pen elevation. The TX channel is for recording the pen
tilt along the x axis. The TY channel is for recording the pen tilt along the y axis. The R channel is for
recording the rotation of the pen about its longitudinal axis. It may be chosen to use
— pen azimuth and pen elevation or
— pen tilt along the x and y axes
with or without the pen rotation. For illustrations see Figure 2 and Figure 3.
The unit of measurement for the pen orientation angles is degree (°).To restore the actual values,
the integer values given in the record body are to be divided by a scaling value given in the channel
description. By choosing appropriate scaling values, different degrees of accuracy can be expressed.
Figure 2 — Pen orientation angles
© ISO/IEC 2014 – All rights reserved 7

Figure 3 — Pen rotation
8 Full format
8.1 Record organisation
A signature/sign time series data record in the full format shall consist of the following data elements
in the given order:
— a general header, containing descriptive information about the structure and contents of the data
record, and
— a record body, containing at least one signature/sign representation.
Figure 4 depicts a signature/sign time series data record in full format. The solid boxes indicate fields
that shall be present. The dashed boxes indicate optional fields. The length of each field in bytes is
indicated in parentheses at the bottom of the corresponding box. The ellipses indicate that more fields
of the same format may follow.
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General header Record body
(15) (variable)
Representation 1
Format identifier Version number Record length Number of Certifi- Representation m
representa- cation
……
tions flag
(4) (4) (4) (2) (1) (variable) (variable)
Representation Representation
header body
(variable) (variable)
Representation Capture date Capture Capture Capture Quality record Channel Number of Sequence of Extended Extended data
length and time device device device descriptions sample points sample points data
tech. ID vendor ID type ID n length
(9)
(4) (1) (2) (2) (variable) (variable) (3) (variable) (2) (variable)
X channel R channel Sample point 1 Sample point n
Number Quality block 1 Quality block q Channel 1
of qual. inclusion description description
…… …… ……
blocks field
(variable) (variable)
(1) (5) (5) (2) (variable) (variable)
Quality Quality Quality Pre- Scaling Minimum Maximum Average Standard X value R value
score algorithm algorithm amble value possible possible deviation
……
vendor ID ID value value
(1) (2) (2) (1) (2) (2) (2) (2) (2) (2) (2)
Figure 4 — Full format
8.2 General header
8.2.1 Structure
The general header shall contain information applicable to all signature/sign representations. The
general header shall consist of the following data elements in the given order:
— a format identifier,
— a version number,
— the length of the data record,
— a field indicating the number of subsequent signature/sign representations, and
— a certification flag.
8.2.2 Format identifier
The format identifier shall be recorded in four bytes. The format identifier shall consist of the three
ASCII characters “SDI” (534449 ) followed by Null (00 ) as a string terminator.
Hex Hex
8.2.3 Version number
The number of the version of this part of ISO/IEC 19794 shall be placed in four bytes. This version
number shall consist of three ASCII characters followed by Null (00 ) as a string terminator. The first
Hex
and second characters represent the major revision number and the third character represents the
minor revision number.
In a signature/sign time series data record following this second edition of this part of ISO/IEC 19794,
the version number shall be 3032 3000 , i.e. “020” (an ASCII ‘0’ followed by an ASCII ‘2’ and an ASCII
Hex
‘0’) followed by Null (00 ) as a string terminator.
Hex
© ISO/IEC 2014 – All rights reserved 9

8.2.4 Length of the data record
The length in bytes of the entire BDIR (biometric data interchange record) shall be recorded in four
bytes. This count shall be the total length of the BDIR including the general header and one or more
representation records.
8.2.5 Number of representations
The total number of representation records contained in the BDIR shall be recorded in two bytes. A
minimum of one representation is required.
8.2.6 Certification flag
The one-byte certification flag indicates whether each representation header includes a certification
record. Its value shall be 00 to indicate that no representation contains a certification record.
Hex
NOTE The certification flag has been added for upward compatibility with later versions of the full format in
which representation headers may contain certification records.
8.3 Record body
8.3.1 Structure
The record body shall consist of a sequence of at least one signature/sign representation. Each
signature/sign representation shall consist of the following data elements in the given order:
— a representation header and
— a representation body.
8.3.2 Representation header
8.3.2.1 Structure
A signature/sign representation header shall contain representation-specific descriptive information. A
representation header shall consist of the following data elements in the given order:
— a representation-length field,
— the capture date and time,
— a capture device technology identifier,
— a capture device vendor identifier,
— a capture device type identifier,
— a quality record,
— a sequence of channel descriptions, and
— a field indicating the number of sample points.
8.3.2.2 Length of the signature/sign representation
The four-byte representation-length field denotes the length in bytes of the representation including the
representation header.
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8.3.2.3 Capture date and time
The capture date and time field shall indicate when the capture of this representation started in
Coordinated Universal Time (UTC). The capture date and time field shall consist of 9 bytes. Its value
shall be encoded in the form given in ISO/IEC 19794-1:2011.
8.3.2.4 Capture device technology identifier
The capture device technology ID shall be encoded in one byte. This field shall indicate the class of
capture device technology used to acquire the captured biometric sample. A value of 00 indicates
Hex
unknown or unspecified technology. See Table 3 for the list of possible values.
Table 3 — Signature/sign capture device technology identifiers
Identifier Capture device technology
00 Unknown or unspecified
Hex
01 Electromagnetic
Hex
02 Semiconductor
Hex
04 Special pen with acceleration sensors
Hex
08 Special pen with optical sensors
Hex
all others Reserved by ISO/IEC JTC 1/SC 37 for future use
8.3.2.5 Capture device vendor identifier
The capture device vendor identifier shall identify the biometric organisation that owns the product
that created the BDIR. The capture device vendor identifier shall be encoded in two bytes carrying a
CBEFF biometric organization identifier (registered by IBIA or other approved registration authority).
A value of all zeros shall indicate that the capture device vendor is unreported.
8.3.2.6 Capture device type identifier
The capture device type identifier shall identify the product type that created the BDIR. It shall be
assigned by the registered product owner or other approved registration authority. Registered product
types shall include all valid combinations of writing tablet and pen as a single product where applicable.
A value of all zeros shall indicate that the capture device type is unreported. If the capture device vendor
identifier is 0000 , then also the capture device type identifier shall be 0000 .
Hex Hex
8.3.2.7 Quality record
The quality record shall consist of a length field followed by zero or more quality blocks. The length field
shall consist of one byte. It shall represent the number of quality blocks as an unsigned integer.
Each quality block shall consist of
— a quality score,
— a quality algorithm vendor identifier, and
— a quality algorithm identifier.
A quality score should express the predicted comparison performance of a representation. A quality
score shall be encoded in one byte as an unsigned integer. Allowed values are
— 0 to 100 with higher values indicating better quality,
— 255, i.e. ff , for indicating that an attempt to calculate a quality score failed.
Hex
© ISO/IEC 2014 – All rights reserved 11

The quality algorithm vendor identifier shall identify the provider of the quality algorithm. The quality
algorithm vendor identifier shall be encoded in two bytes carrying a CBEFF biometric organization
identifier (registered by IBIA or other approved registration authority). A value of all zeros shall indicate
that the quality algorithm vendor is unreported.
The quality algorithm identifier shall identify the vendor’s quality algorithm that created the quality
score. It shall be assigned by the provider of the quality algorithm or an approved registration authority.
The quality algorithm identifier shall be encoded in two bytes. A value of all zeros shall indicate that the
quality algorithm is unreported.
8.3.2.8 Channel descriptions
8.3.2.8.1 Channel inclusion field
The channel descriptions field shall begin with a channel inclusion field indicating the presence or
absence of channels.
The channel inclusion field shall consist of two bytes. Each bit shall correspond to a channel as shown
in Table 4. A bit value of 1 shall encode the presence of the corresponding channel; a bit value of 0 shall
encode the absence of the corresponding channel.
Table 4 — Format of the channel inclusion field
Channel name Octet Bit position
X 8 (msb)
Y 7
Z 6
VX 5
VY 4
AX 3
AY 2
T 1 (lsb)
DT 8 (msb)
F 7
S 6
TX 5
TY 4
A 3
E 2
R 1 (lsb)
The channel inclusion field shall be followed by a sequence of channel descriptions for the channels
indicated as present in the channel inclusion field. The order of the channel descriptions is determined
by the order of indicated inclusion within the channel inclusion field starting with the X channel. The
channel descriptions are mandatory for all channels present in the signature/sign time series data
record.
EXAMPLE Figure 5 shows the channel inclusion field for signature/sign time series data including the
channels X, Y, T, F, S, A, E and R.
12 © ISO/IEC 2014 – All rights reserved

Octet 1 Octet 2
1 1 0 0 0 0 0 1 0 1 1 0 0 1 1 1
Figure 5 — Example of a channel inclusion field
8.3.2.8.2 Channel description preamble
Each channel description shall begin with a preamble. Each channel description preamble shall consist
of one byte.
Each of the bits 4 through 8 of a channel description preamble shall correspond to a channel attribute as
shown in Table 5. A bit value of 1 shall encode the presence of the corresponding channel attribute; a bit
value of 0 shall encode the absence of the corresponding channel attribute. If any of the bits 4 through 8
of a channel description preamble are set to 1, the preamble shall be followed by a sequence of channel
attributes in the same order as indicated in the preamble starting with the scaling value.
Table 5 — Format of a channel description preamble
Channel attribute Bit position
Scaling value 8 (msb)
Minimum possible channel value 7
Maximum possible channel value 6
Average of the channel values 5
Standard deviation of the channel values 4
Constant value 3
Removal of the linear component with respect to time 2
Reserved by ISO/IEC JTC 1/SC 37 for future use 1 (lsb)
A value of 1 for bit 3 of a channel description preamble shall indicate that the value of this channel is
constant. If bit 3 of a channel description preamble is set to 1, then this channel shall be absent in the
representation body even though the representation header indicates the presence of the channel. If the
channel description contains a scaling value, then the constant value of this channel shall be 1 divided
by the scaling value.
EXAMPLE 1 Bit 3 of the DT channel description preamble can be used to indicate a uniform sampling rate.
NOTE 1 For all other channels except the DT channel, bit 3 of the channel description preamble should be 0.
A value of 1 for bit 2 of a channel description preamble shall indicate that the linear component of the
regression line for this channel has been removed from this channel.
EXAMPLE 2 Bit 2 of the X channel description preamble can be used to indicate that the linear component of
the X-on-T regression line (which may be present due to writing along a horizontal line) has been removed from
the X channel in order to map the X values to a smaller range.
NOTE 2 Since the removal of a linear trend with respect to time is not practically relevant for the time channel,
the value of 1 should not be used for bit 2 of the channel description preamble of the T channel.
The unused trailing bit of the preamble shall have value 0 and is reserved by ISO/IEC JTC 1/SC 37 for
future use.
8.3.2.8.3 Scaling value
If present, scaling values shall consist of two bytes. The five most significant bits of the first byte shall
constitute the exponent field E, and the remaining eleven bits shall constitute the fraction field F.
© ISO/IEC 2014 – All rights reserved 13

The exponent field E contains an unsigned integer representing the base 2 exponent of the scaling
value biased by 16. For the exponent, signed integer values in the range from –16 to 15 are possible.
For encoding the exponent value, 16 is to be added in order to get an unsigned value. For decoding the
exponent value, 16 is to be subtracted from the contents of E.
The fraction field F contains the bit field that lies, in binary notation, to the right of the leading bit and
the binary point of the scaling value’s coefficient lying in the range 1 ≤ coefficient < 2.
The scaling value s is calculated by
 F 
E−16
s =+1 ⋅2 .
 
 2 
EXAMPLE s = 1 is represented by a value of 00 in the fraction field F and a value of 10 in the exponent
Hex Hex
field E.
–16 15
The scaling value has a range from 2 to (1 + 2047/2048)·2 , i.e. from 0,000 015 258 789 062 5 to
65 520.
The channel values in the representation body as well as the minimum, maximum, and average channel
values and the standard deviation in the representation header are to be divided by the corresponding
scaling value to obtain their actual values.
If the scaling value is absent, the calibration of the corresponding channel is unknown.
8.3.2.8.4 Minimum and maximum possible channel values
If present, the minimum and maximum possible channel values shall indicate the scaled range of values
that the deployed capture device may deliver for the corresponding channel.
For the minimum and maximum possible channel values of the Z, T, DT, F, A, E, and R channels, integer
values in the range from 0 to 65 535 are allowed. These values shall be encoded in two bytes as unsigned
integers.
For the minimum and maximum possible channel values of the X, Y, VX, VY, AX, AY, TX, and TY channels,
integer values in the range from –32768 to 32767 are allowed. These values shall be encoded in two
bytes as unsigned integers after adding 32768 to each value. Hence, for non-negative numbers, bit 8 of
the most significant byte has the value 1; for negative numbers, bit 8 of the most significant byte has the
value 0. For decoding these values, 32768 is to be subtracted from each recorded value.
14 © ISO/IEC 2014 – All rights reserved

8.3.2.8.5 Average and standard deviation of the channel values
If present, the average of the channel values shall be the arithmetic mean c , rounded to the nearest
integer, of all values c (1≤≤iN where N is the number of sample points) for the corresponding channel
i
within a signature/sign time series data record:
N
c = c .
∑ i
N
i=1
If present, the standard deviation of the channel values shall be the empirical standard deviation σ ,
c
rounded to the nearest integer, of all values c (1≤≤iN ) for the corresponding channel within a
i
signature/sign time series data record:
N
1 2
σ =−cc .
()
ci∑
N
i=1
For the averages of the Z, T, DT, F, A, E, and R channels as well as for the standard deviations of all
channels, integer values in the range from 0 to 65 535 are allowed. These values shall be encoded in two
bytes as unsigned integers.
For the averages of the X, Y, VX, VY, AX, AY, TX, and TY channels, integer values in the range from 32768
to 32767 are allowed. These values shall be encoded in two bytes as
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