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Adaptive optics speeds up airport immigration

15 Jan 2009

An iris-recognition system that uses adaptive optics to compensate for subject motion could move this biometric technique into mainstream security applications. Marie Freebody speaks to Phil Tusa of AOptix to discuss the development in more detail.

Any traveller who has used iris recognition as part of airport immigration will probably agree that it is a tedious process involving a complex alignment procedure. Now, thanks to adaptive optics technology origin-ally developed for deep-space astronomy, a remarkably straightforward iris recognition system has been developed with a significantly larger capture zone.

"All other systems require the subject to position their eyes within a very small capture zone in order to allow for proper centring and focusing of the imager," Phil Tusa, vice-president of biometrics at AOptix, told OLE. "This is the first iris-recognition scheme to employ adaptive optics within an intelligent system design, which can automatically find and track the subject's eyes with no effort required by the subject."

Why iris recognition?
Iris recognition is particularly attractive for security applications since the iris is an extremely reliable identifier of an individual. However, the biggest technical hurdle standing in the way of the widespread deployment of these systems is obtaining accurate images in a simple manner that is "user friendly" to the widest range of people. Current systems only operate at short ranges and often users have great difficulty in positioning themselves properly, which leads to either poor images or no image at all being captured.

"The biometrics market and customer base have voiced great interest in biometrics products that advance 'subject human factors' or usability, especially for large-scale deployments such as the UK national ID programme or immigration control facilities at Heathrow and other UK airports," explained Tusa. "The goal of our design employing adaptive optics is to greatly improve subject usability, which is recognized by experts in the UK as the chief obstacle to adoption."

AOptix was founded in 2000 by a group of scientists from the University of Hawaii's Center for Adaptive Optics. Realizing the potential of adaptive optics to extend beyond the correction of distortions from the atmosphere to the compensation of subject motion, the scientists applied the technology to solve challenging problems in biometrics. The company now employs around 75 full-time staff, the vast majority of whom are in R&D and engineering and who have pioneered this new technology.

"This is the first iris-recognition system to employ adaptive optics, and so the R&D and engineering teams have had to invent the system architecture, while meeting stringent targets for commercialization, such as manufacturability, reliability, serviceability and cost," explained Tusa. "The engineering team has designed its own cameras and the company makes its own wavefront sensors and deformable mirrors."

The result is InSight, an iris-recognition system with an operational distance of 2 m and a large capture zone of around 75 cm3 (1 m deep, 1 m tall and 0.75 m wide). This means that at a 2 m stand-off distance, the system can handle heights ranging from about 1 m (3 ft 4 inch, or 40 inch) to about 2 m (6 ft 7 inch, or 80 inch), or even accommodate subjects who are in wheelchairs.

"The subject merely needs to step into this extraordinarily large capture zone, look at the camera and open their eyes," explained Tusa. "The system automatically finds the subject, locates their eyes and then locks on with the adaptive optics subsystem while the iris-capture camera automatically acquires a set of very high-quality images."

Adaptive optics tracks movement
Adaptive optics is crucial to the AOptix design and lends itself particularly well to iris recognition applications. It enables very long stand-off distances and fully automates subject tracking ensuring that images are always centred and in focus.

"Our approach to iris recognition is a two-stage process in which the system employs a wide-field visible-light camera to automatically find the subject's face and eyes through a face detection algorithm derived from face-recognition technology," explained Tusa. "The first stage hands over the location of the subject's eyes to a closed-loop control subsystem in the second stage, which uses adaptive optics for fine tracking and focus while a high-resolution infrared camera captures iris images of excellent quality."

In more detail, a deformable mirror in the optical path changes shape at very high speeds to apply a cancelling distortion to the light. A wavefront sensor locks in on a reference, and the closed-loop control system sends appropriate commands to the deformable mirror for image compensation.

The wavefront sensor and closed-loop control system operate in real time relative to the motion of the subject. This means that the system can acquire the subject's iris and capture multiple images of a single eye in 2 s or less. Throughput rates can be up to 15 subjects per minute in queuing applications.

Since the adaptive optics constantly corrects for subject motion in real time, it eliminates motion blur – a common cause of image degradation. Real-time tracking and steering enables the system to use narrow-field, high-magnification objective lenses that deliver very high spatial resolution.

"We have designed the system to handle normal head motion, but not walking," said Tusa. "In addition, InSight substantially exceeds the ISO standard requirement resolution of two line pairs per millimetre at 60% contrast."

As well as the crucial adaptive optics elements, InSight also contains on-board infrared LEDs for illumination that operate in the range of about 800–850 nm. On-board face-detection software automatically determines if there is a person in the capture zone, which enables the system to operate autonomously.

Iris recognition deployment
According to Tusa, AOptix has identified six different market and application areas that could benefit from its InSight system. These include border crossing and immigration control, national and regional ID card programmes, aviation security, governmental access control, commercial access control and law enforcement.

"These applications fall into two general categories, one of which is enrolment, in which biometrics are used to ensure that each person is granted only one credential. The second category is authentication, in which the subject's identification is verified at a checkpoint station through biometric capture," commented Tusa.

Although the company has no functional deployments at present, it does have two systems in beta test programmes, one of which is in a border crossing application and the other is in aviation security. Commercial shipments of InSight are expected to begin in the second quarter of 2009.

In the meantime, AOptix continues to work on extending the range of situations in which its system can operate. "There will always be a need to improve subject capture robustness, including subjects with head coverings and veils," concluded Tusa. "We are investigating improvements in subject acquisition algorithms in order to achieve this."

• This article originally appeared in the January 2009 issue of Optics & Laser Europe magazine.

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