
format, as a vector of individual features that were
extracted from the captured biometric sample. This
process is quite transparent as for example in the finger-
print analysis: The essential features of a fingerprint are
minutia locations (ridge endings and ridge bifurcations)
and directions and potentially extended data such as
ridge count information between minutia points. This
data is relevant information for almost every fingerprint
comparison subsystem and standardizing a minutia for-
mat was a straightforward process [8].
These feature-based format standards encode only
the structured information – none of the various con-
cepts and algorithms that extract minutia points has
been included in the standardization work. Many
approaches for these tasks have been published in the
academic literature; nevertheless, solutions in products
are considered as intellectual property of the suppliers
and therefore usually not disclosed.
Furthermore, it became necessary to cope with
different cultures in identifying minutia points. Thus
minutia definitions based on ridge ending versus defi-
nitions based on valley skeleton bifurcations became
sub-types of the standard. While these ambiguities
cover the variety of approaches of indu strial imple-
mentations, an impressive interoperability can still
be achieved, a s it was proven in two independent
studies [9, 10].
Requirements from biometric recognition applica-
tions are quite diverse: Some applications are tuned on
high biometric performance (low error rates) in an
identification scenario. Other applications are tuned
to operate with a low capacity token in a verification
scenario. Where database systems are designed, the
record format sub-type is the appropriate encoding.
In other applications the token capacity may be ex-
tremely limited and thus the card format sub-type that
exists in ISO/IEC IS 19794 for the fingerprint data
formats in Part 2, 3 and 8 is the adequate encoding.
Other parts such as 19794-10, which specifies the
encoding of the hand silhouette, have been designed
to serve implementations that are constrained by stor-
age space. In general the concept of compact encoding
with the card format is to reduce the data size of a BDB
down to its limits. This can be achieved when necessary
parameters in the metadata are fixed to standard
values, which makes it obsolete to store the header
information along with each individual record.
For all data interchange formats it is essential to
store along with the representation of the biometric
characteristic essential information (metadata) on the
capturing processing and the generation of the sample.
Note that in the case of the card format sub-type fixed
values may be required as discussed above. Metadata
that is stored along with the biometric data (the bio-
metric sample at any stage of processing) includes
information such as size and resolution of the image
and (e.g., fingerprint image, face image) but also rele-
vant data that impacted the data capturing process:
Examples for such metadata are the Capture Device
Type ID, that identifies uniquely the device that was
used for the acquisition of the biometric sample and
also the impression type of a fingerprint sample, which
could be a plain live scan, a rolled live scan, non-live
scan or stemming from a swipe sensor. Furthermore,
the quality of the biometric sample is an essential
information that must be encoded in the metadata.
In general, an overall assessment of the sample quality
is stored on a scale from 0 to 100, while some formats
allow additional local quality assessment such as the
fingerprint zonal quality data or minutia quality in
various fingerprint encoding standards [8, 11]. The
rationale behind this quality recording is to provide
information that might weigh into a recapture deci-
sion, or to drive a failure to acquire decision . A bio-
metric system may need to exercise quality control on
biometric samples, especially enrollment, to assure
strong performance, especially for identification sys-
tems. Furthermore, multimodal comparison solutions
should utilize quality to weigh the decisions from the
various comparison subsystem to improve biometric per-
formance. Details on how to combine and fuse different
information channels can be found in the ISO technical
report on multibiometric fusion [12]. A local qualit y
assessment may also be very meaningful as environ-
mental factors (such as different pressure, moisture, or
sweat may locally degrade the image quality of a fin-
gerprint) and thus degrade biometric performance.
In general the metadata in an ISO data interchange
format is subdivided into information related to the
entire record which is stored in the general header and
specific information related to one individual view,
which is stored in the view header. The existence of
multiple views is of course dependent on the applica-
tion and the respective modality used. In the case of a
fingerprint recognition system it is a common ap-
proach, in order to achieve a higher recognition per-
formance, to store multiple views such as right and left
index finger together as separate views in one BDB.
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