Page 63 - Automated Fingerprint Identification Systems (AFIS)

48 AUTOMATED FINGERPRINT IDENTIFICATION SYSTEMS

By the next year, Interpol held another meeting and agreed to develop an
Interpol implementation of the ANSI-NIST standard. Mr. Chris Coombs of the
Metropolitan Police, London, agreed to lead the effort. He was quickly able to
modify the UK implementation so that it was an Interpol Implementation. After
it was approved, the UK dropped its document and adopted the Interpol Imple-
mentation. The current version is the Interpol Implementation (ANSI/NIST ITL
1-2000) Version No. 4—19 November 2002.
In the 2000 workshops at NIST, the issue of how to represent rich alphabets
(e.g., Japanese) that required more characters than those supported by the
ASCII character set had been raised. The decision made was clever—the Type
1 record would always be in ASCII, but it would have an optional data field to
show if the Type 2 record was in Unicode. This permitted countries to exchange
names in their native alphabet set.

2.7.3 IMAGE QUALITY SPECIFICATIONS
After the EFTS was published, the FBI issued Appendix F: Image Quality Specifi-
cations (IQS). Image quality is perhaps the most significant driver of AFIS
performance. By selecting ANSI/NIST Type 4 records, the FBI had already
ensured that images would be captured at 500ppi or higher, with 8 bits of gray-
scale and transmitted at 500ppi (with a small tolerance for variation). But they
had not provided any standards for the quality of the optics, the signal pro-
cessing, the printers, or the displays. The importance of all elements of the
“image chain” can be seen by envisioning a scanner connected to a PC. If a
color picture is scanned in color at 2,000ppi (24 bits per pixel or more) and is
displayed on a 72ppi black and white monitor at a 1:1 resolution, there is far
more information going into the digital image than coming out. There is a
need to specify all aspects of the process to minimize data loss at any point in
the chain.
There were no issues with the IQS specifications for printers or monitors; all
the interest was and still is focused on capture devices. The IQS standard lists
six data capture attributes that specify an image chain in engineering terms
(e.g., modulation transfer function), since it is very difficult and often subjec-
tive to describe image quality in any other way. Industry pushed back against
the Appendix F IQS and asked for relief on two of the elements for data acqui-
sition. The FBI responded with Appendix G: Interim Image Quality Specifications
for Scanners for use until IAFIS went operational.
The IQS image acquisition specifications were designed for optical systems
such as flat bed scanners. Using it on livescan devices and single finger solid-
state devices is much more difficult. Eventually, the FBI, working with MITRE,
established a self-certification process for industry. After the certification tests