ISO/IEC 19794-10:2007

INTERNATIONAL ISO/IEC
STANDARD 19794-10
First edition
2007-06-01

Information technology — Biometric data
interchange formats —
Part 10:
Hand geometry silhouette data
Technologies de l'information — Formats d'échange de données
biométriques —
Partie 10: Données de la silhouette de la géométrie de la main




Reference number
ISO/IEC 19794-10:2007(E)
©
ISO/IEC 2007

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ISO/IEC 19794-10:2007(E)
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ISO/IEC 19794-10:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Conformance. 1
3 Normative references . 1
4 Terms and definitions. 1
5 General. 3
5.1 Byte order . 3
5.2 Use of FCCs for data compression. 3
5.3 CBEFF Format owner and format type. 4
6 Silhouette acquisition requirements. 4
6.1 Overview . 4
6.2 Hand orientation . 4
6.3 Aspect ratio . 5
6.4 Presentation . 6
6.5 Coordinate system. 6
7 Hand geometry interchange format (BDB format) . 7
7.1 General record header. 8
7.2 Hand geometry view record (HGVR). 9
Annex A (informative) Sample hand geometry data packet. 17
Annex B (informative) Best practices. 19

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ISO/IEC 19794-10:2007(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 19794-10 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 37, Biometrics.
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
The following part is under preparation:
⎯ Part 11: Signature/sign processed dynamic data
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ISO/IEC 19794-10:2007(E)
Introduction
In the Access Control and Time Management communities, hand geometry has been an option to add
biometrics to traditional security systems. While several hand geometry systems have been developed into
products, each vendor has traditionally relied on a proprietary algorithm and has stored a proprietary template.
This has made it impossible to transfer data from one vendor’s system to another’s, forcing end users to sole-
source their hand geometry solution. To allow integration of hand geometry systems from multiple vendors, a
nonproprietary interchange format must be adopted.
This part of ISO/IEC 19794 is intended to provide a data interchange format (a CBEFF biometric data block –
BDB) for applications requiring an interoperable hand geometry record. The information consists of a variety
of mandatory and optional items including data capture parameters, standardized hand position 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 hand geometry.
While this part of ISO/IEC 19794 mandates a particular data format, it does not mandate a particular algorithm.
For example, a user may be enrolled on a system from one vendor and verified on a system from another.
Because hand geometry products have historically relied on measurements taken from a hand silhouette, this
format stores hand silhouette data rather than color or grayscale image data. To increase the flexibility of the
data format, provisions have been made to store views of the left and right hands, in addition to multiple views
of each hand. Specific implementations of this part of ISO/IEC 19794 that are constrained by storage space
(such as smart card applications) may wish to limit the number of views stored for each hand. Such limitations
are outside the scope of this part of ISO/IEC 19794, but reduced choices can prejudice interoperability.
It is well known that the presentation of a biometric sample affects algorithm performance. While image
acquisition and hand placement requirements are outside the scope of this part of ISO/IEC 19794, Annex B is
provided as guidance for those wishing to adhere to industry “best practices”.

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INTERNATIONAL STANDARD ISO/IEC 19794-10:2007(E)

Information technology — Biometric data interchange
formats —
Part 10:
Hand geometry silhouette data
1 Scope
This part of ISO/IEC 19794 specifies a data interchange format (a CBEFF biometric data block – BDB) that
can be used for storing, recording and transmitting the information obtained from a hand silhouette.
This part of ISO/IEC 19794 defines the content, format and units of measurement for the exchange of hand
silhouette data in a BDB.
Information formatted in accordance with this part of ISO/IEC 19794 can be recorded on machine-readable
media or transmitted by data communication between systems.
2 Conformance
A biometric data block conforms to this part of ISO/IEC 19794 if it satisfies the format requirements specified
within the normative clauses of this part of ISO/IEC 19794 and has internal consistency based on capture
from an actual hand.
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 19785-1, Information technology — Common Biometric Exchange Formats Framework — Part 1:
Data element specification
ISO/IEC 19784-1, Information technology — Biometric application programming interface — BioAPI
specification
4 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
4.1
biometric data block
BDB
block of data with a defined format that contains one or more biometric samples or biometric templates
NOTE In the case of this part of ISO/IEC 19794, the BDB contains the hand silhouette of one or both hands, perhaps
with multiple views.
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ISO/IEC 19794-10:2007(E)
4.2
biometric sample
information obtained from a biometric device, either directly or after further processing
NOTE The silhouette of a hand is an example of a biometric sample.
4.3
camera point of view
effective location and orientation of a camera that would result in the observed hand silhouette
NOTE The effective location is specified rather than the actual location due to the possibility of algorithmic
transformations and various hand-scanning technologies such as movable linear arrays, etc.
4.4
capture
process of taking a biometric sample from an end user
4.5
Freeman Chain Code
FCC
compact method for representing the contours of an object
NOTE First made popular by Herbert Freeman.
4.6
image resolution
number of pixels per unit distance in the interchanged image
NOTE This may be the result of processing a captured image. The original captured image may have been
subsampled, scaled, interpolated or otherwise processed to produce a silhouette suitable for automated hand recognition.
4.7
live capture
process of capturing a biometric sample through an interaction between an end user and a biometric system
4.8
hand geometry view record
HGVR
block of data that contains a hand silhouette captured from one camera point of view during one hand
placement
NOTE The block contains metadata, silhouette data and optional extended data.
4.9
pixel
picture element located on an n by m matrix of picture elements, where n is the horizontal component and m
is the vertical component
4.10
platen
reference surface on which a hand is placed during imaging
NOTE The platen will often contain alignment pins to promote repeatable finger placement.
4.11
side-view
data taken from the thumb side or the little-finger side of the hand
cf. top-view
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ISO/IEC 19794-10:2007(E)
4.12
side-view reference plane
physical or imaginary plane on which the side-view silhouette is projected
4.13
tip
〈finger〉 end of the fingernail or the end of the flesh at the end of the finger, whichever produces the longer
silhouette
NOTE See Figure 3 a).
4.14
top-view
data taken from the palm side of the hand or the back side of the hand
cf. side-view
4.15
web
area connecting two adjacent fingers at their connection point to the palm
NOTE See Figure 3 a).
5 General
5.1 Byte order
For the purposes of transfer and storage of the BDB, the more significant bytes of any multi-byte quantity are
present before less significant bytes.
NOTE This is commonly referred to as a “big-endian” encoding, or “network byte” order.
Within a byte, the bits are numbered from 0 to 7, where 7 is the “most significant bit” (MSB) and bit 0 the “least
significant bit” (LSB).
5.2 Use of FCCs for data compression
To conserve space, the hand silhouette shall be recorded using a Freeman Chain Code (FCC).
NOTE This representation requires only 2-3 bits per pixel along the perimeter of the silhouette. The FCC has long
been used to represent black-and-white contours.
Each element of the FCC shall be stored immediately following its predecessor, without regard to byte
boundaries. If necessary, the silhouette shall be padded with trailing zeros to ensure that the BDB is an
integral number of octets.
Two forms of FCC are supported by this part of ISO/IEC 19794. The 8-way FCC uses three bits per pixel to
represent the direction from one pixel to an adjacent pixel. The 4-way FCC uses two bits per pixel by
eliminating the diagonal directions allowed in the 8-way FCC.
Silhouette data contained in BDBs conforming to this part of ISO/IEC 19794 (see clause 2) shall be body-
centric and not grid centric FCCs as shown in Figure 1 (starting/ending points are shown as squares,
intermediate points as circles).
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ISO/IEC 19794-10:2007(E)




a) Body-centric 8-way FCC = 4,4,4,7,7,0,2,2 b) Grid-centric 8-way FCC = 4,4,4,5,7,7,7,0,1,2,2,3
Figure 1 — Body-centric and grid-centric Freeman Chain Code

5.3 CBEFF Format owner and format type
The BDB format specified in this part of ISO/IEC 19794 shall be embedded in a CBEFF-compliant Biometric
Information Record (BIR) according to ISO/IEC 19785-1. The structure of a hand geometry silhouette BIR is
depicted in Figure 2, where the CBEFF Standard Biometric Header (SBH) is mandatory, and the CBEFF
Security Block (SB) is optional.

CBEFF Hand Geometry CBEFF

SBH Silhouette BDB SB
Figure 2 — Overview of a hand geometry silhouette biometric information record
NOTE The CBEFF signature holds data that enables the integrity and/or the originator of the hand geometry
silhouette BIR to be verified [electronic signature or message authentication code (MAC)].
The CBEFF Format Owner identifier assigned by the CBEFF Registration Authority to ISO/IEC JTC 1/SC 37
shall be used in the CBEFF SBH associated with the BDB. This is the sixteen-bit value 0x0101 (hexadecimal
101 or decimal 257).
There is one CBEFF Format Type code assigned to the data record specified in this part of 19794. This code
shall be included in the CBEFF SBH. The sixteen-bit value 0x0018 (hexadecimal 18 or decimal 24) shall be
used for data records specified in this part of 19794.
6 Silhouette acquisition requirements
6.1 Overview
It is not the purpose of this part of ISO/IEC 19794 to specify the method of data capture or the order of
process steps used to capture the silhouette. However, after data acquisition and processing, each silhouette
shall have the orientation shown in Figure 3 a) for top-view images, or Figure 3 b) for side-view images.
6.2 Hand orientation
The silhouette shall represent either the left or right hand and shall be presented in one of the orientations
depicted in Figures 3 a) and 3 b).
NOTE Silhouettes taken from a left hand pinned platen shall be flipped (mirror image) to match the form of Figure 3a).
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ISO/IEC 19794-10:2007(E)

Tip
3 2 1

4 0
Tip

Web
5 6 7
8-way FCC Directions
Web
Tip
1 Web

Tip
2 0
Web

3
4-way FCC Directions

a)  Top-view images

3 2 1



4 0

5 6 7
8-way FCC Directions
1


2 0



3

4-way FCC Directions
b)  Side-view images
Figure 3 — Standard hand orientation for images
6.3 Aspect ratio
The aspect ratio shall be 1:1, within a tolerance of ± 2%.
NOTE 1 The following example may be useful in calculating the aspect ratio: Assume a grid with 25 mm spacing is
placed at the camera centerline, with the grid normal to the centerline axis. The aspect ratio of a captured image may be
calculated by counting the number of pixels between the grid lines ± 25 mm from the origin. A system that counts
100 pixels in the x direction and 108 pixels in the y direction has an 8% error compared to the ideal 1:1 aspect ratio.
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ISO/IEC 19794-10:2007(E)
NOTE 2 “Aspect ratio” relates to the digital characteristics of the stored data, not to physical characteristics of the
scanning device.
6.4 Presentation
In order to obtain the best hand recognition performance and interoperability, certain mandatory requirements
regarding presentation of the hand must be observed. Optional “best practices” for hand placement, platen
design, and optical system design are addressed in Annex B.
Mandatory requirements are as follows.
⎯ The starting point shall be in the rightmost column of the silhouette in Figure 1, at the uppermost row
occupied by the silhouette in that column. Successive points shall trace the outline in a counterclockwise
direction.
⎯ The silhouette shall be a closed shape (i.e., it shall have no gaps in the outline, and the final outline point
shall be collocated with the starting point).
⎯ The starting point shall occur exactly twice in the silhouette, as the first and last points only (the silhouette
will not cross through the starting point at any other time).
⎯ The right column shall be vertical (i.e., the penultimate point shall occur directly below the starting point,
and no points occur to the right of the starting point).
6.5 Coordinate system
For imaging systems utilizing optical cameras, interoperability is influenced by the location of the camera
relative to the hand. As such, this part of ISO/IEC 19794 includes fields for recording the camera point of view
of the imaging device used to capture the hand silhouette. This section defines the coordinate system used in
recording camera point of view.
Figure 4 shows the relationship between the camera points of view, the platen, and the side-view reference
plane. The global origin (0,0,0 in 3D space) is defined as the point at which the top-view optical axis intersects
the platen. The side-view origin, which is defined relative to the global origin, is the point at which the side-
view optical axis intersects the side-view reference plane. The platen shall form a right angle with the side-
view reference plane.
For imaging systems utilizing optical cameras, the optical axis for top-view images shall be orthogonal to the
platen. Likewise, the optical axis for side-view images shall be orthogonal to the side-view reference plane.
NOTE The reason for the orthogonality requirements is that interoperability decreases as the optical axes diverge
from the normal orthogonal positions.

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ISO/IEC 19794-10:2007(E)




Implicit in data format:
Global origin = (0,0,0)


Explicit in data format (relative to Origin):

Top-view position (x,y,z)
Top-view
Side-view position (x,y,z)
Side-view origin  (x,y,z)

Silhouette starting point (x,y)


O = Top-view (Global) Origin
t
O = Side-view Origin

s

1
2
 Z
O

s
0

3
2
Side-view


3 1
Y
   O 0
t


      X 90°

NOTE 4-way FCC directions shown for top and side views.
Figure 4 — Coordinate system linking top and side view images
7 Hand geometry interchange format (BDB format)
Silhouette data shall be represented in a common format, containing both basic and extended data. With the
exception of the Format Identifier and the Version number, which are null-terminated ASCII character strings,
all data is represented in binary format. There are no record separators or field tags; fields are parsed by byte
count.
The BDB format specified in this part of ISO/IEC 19794 shall be embedded in a CBEFF-compliant Biometric
Information Record (BIR) as described in 5.3.
The organization of the BDB is as follows:
⎯ a fixed-length (15-byte) general record header containing information about the overall record;
⎯ one or more variable-length hand geometry view records (HGVRs), each containing a single hand
silhouette.
Figure 5 depicts the hierarchy of BDB elements within a CBEFF BIR, where the CBEFF SBH is mandatory,
and the CBEFF SB is optional.



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ISO/IEC 19794-10:2007(E)




CBEFF Hand Geometry CBEFF

SBH Silhouette BDB SB(optional)


Hand Geometry HGVR #1 HGVR #2 . . . HGVR #N

General Header (mandatory) (optional) (optional)

15 bytes


metadata silhouette extended
(mandatory) (mandatory) (optional)

25 bytes variable variable
Figure 5 — Hierarchy of BDB elements

7.1 General record header
The general record header is specified in Table 1.
Table 1 — Hand geometry general record header
Field Size Valid values Notes
Format identifier 4 bytes 0x484E4400 “HND” – Hand Geometry Record
(‘H’ ‘N’ ‘D’ 0x00)
Version number 4 bytes 0x30313000 The current version is 1, and the revision
level is 0
('0' '1' '0' 0x00)
Record length 4 bytes Size of the entire BDB, including this header
and multiple HGVRs
Number of HGVRs 1 byte Number of HGVRs in the record
Reserved for future use 2 bytes Bytes shall be set to zero by producers of a
BDB, and should be ignored by users of the
BDB.

7.1.1 Format identifier
The BDB shall begin with the three ASCII characters “HND” to identify the record, followed by a zero byte as a
null string terminator.

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ISO/IEC 19794-10:2007(E)
7.1.2 Version number
The number for the version of this part of ISO/IEC 19794 used for constructing the BDB shall be placed in four
bytes. This version number shall consist of three ASCII numerals followed by a zero byte as a NULL string
terminator. The first and second characters will represent the major version number and the third character
will represent the minor revision number. Upon approval of this specification, the version number shall be
“010” – Version 1 revision 0.
7.1.3 Record length
This four-byte field indicates the total size of the BDB, including the general header and one or more HGVR
(see 7.2).
7.1.4 Number of HGVRs
The number of hand silhouettes included in the BDB shall be recorded in one byte. Multiple silhouettes of the
same hand shall be counted separately. Top-view and side-view silhouettes that are linked by the same
HGVR index (see 7.2.2) shall be counted separately.
7.1.5 Reserved for future use
These bytes are not used, and are only a placeholder for future use. Bytes shall be set to zero by producers of
a BDB, and should be ignored by users of the BDB.
7.2 Hand geometry view record (HGVR)
The HGVR provides metadata, silhouette data, and possibly extended data for one view of a single hand
placement. Table 2 defines the location and description of the 25-byte metadata, variable-length silhouette
data, and optional variable-length extended data.

Table 2 — Hand geometry view record
Field Size Valid values Notes
Length of HGVR 2 bytes Includes metadata, silhouette, and
extended data
HGVR index 1 byte Used for linking groups of images to the
same capture sequence
Hand identifier 1 byte Bitmapped field. See 7.2.3.
Hand integrity 1 byte Bit-mapped field. See 7.2.4.
Data resolution 1 byte 0, 1-255 Pixels per centimeter
0 = unknown
Distortion 1 byte signed value, increments of 0,1%
0x80 = unknown
Silhouette quality 3 bytes 0x0000XX The two high bytes are zero, the low byte
has a valid range of
0-100
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Camera X position 1 byte Signed distance in FCC Direction 4 and 2,
for a 8-way and 4-way FCC, respectively.
127 = more positive than 126
128 = unknown
129 = more negative than 130
else XPOS = millimeters / 4
Camera Y position 1 byte Signed distance in FCC Direction 2 and 1,
for a 8-way and 4-way FCC, respectively.
127 = more positive than 126
128 = unknown
129 = more negative than 130
else YPOS = millimeters / 4
Camera Z position 1 byte Distance normal to the platen
255 = unknown
254 = greater than max value
else ZPOS = millimeters / 4
Target X position 1 byte Signed distance in FCC Direction 4 and 2,
for a 8-way and 4-way FCC, respectively.
127 = more positive than 126
128 = unknown
129 = more negative than 130
else XPOS = millimeters / 4
Target Y position 1 byte Signed distance in FCC Direction 2 and 1,
for a 8-way and 4-way FCC, respectively.
127 = more positive than 126
128 = unknown
129 = more negative than 130
else YPOS = millimeters / 4
Target Z position 1 byte Signed distance above the platen
127 = more positive than 126
128 = unknown
129 = more negative than 130
else ZPOS = millimeters / 4

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ISO/IEC 19794-10:2007(E)
X Position of silhouette starting 1 bytes Distance in FCC Direction 4 and 2, for a 8-
point way and 4-way FCC, respectively.
127 = more positive than 126
128 = unknown
129 = more negative than 130
else XPOS = millimeters / 4
Y Position of silhouette starting 1 bytes Distance in FCC Direction 2 and 1, for a 8-
point way and 4-way FCC, respectively.
127 = more positive than 126
128 = unknown
129 = more negative than 130
else YPOS = millimeters / 4
Data compression algorithm 1 byte 0-1 0 = 8-way FCC
1 = 4-way FCC
Hand Scanning Technology 1 byte 0-2 0 = unspecified
1 = optical camera
2 = linear scanning array
3-255 = reserved for future use
Extended data length 2 bytes Length, in bytes, of extended data
associated with this HGVR
Reserved for future use 3 bytes Bytes shall be set to zero by producers of
a BDB in this version of this part of
ISO/IEC 19794, and should be ignored by
users of the BDB.
Silhouette data variable This is the silhouette data block
Extended data variable Associated with CBEFF format owner

7.2.1 Length of HGVR
This two-byte field contains the length in bytes of a particular HGVR. It shall specify the total number of bytes
including the length of the metadata, the silhouette data and the extended data for that view.
7.2.2 HGVR index
This one-byte field is assigned to an HGVR when it is captured.
NOTE Where several HGVRs are captured at the same time, it is normal (but not required) to assign the same
HGVR index to all the HGVRs. When HGVRs are captured separately, distinct HGVR indices are normally assigned.
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ISO/IEC 19794-10:2007(E)
7.2.3 Hand identifier
This bitmapped one-byte field shall identify the hand and camera orientation used to capture the associated
hand (or subset thereof) silhouette. Bits 0-4 indicate which fingers the system attempts to image, where bit-
values of one indicate that the system attempts to image the indicated finger. The mapping is as follows:

View indicator Hand Thumb Index Middle Ring L
...