Gil Abramovich

Stand-off Iris Recognition System

The iris is a highly accurate biometric identifier. However widespread adoption is hindered by the difficulty of capturing high-quality iris images with minimal user co-operation. This paper describes a first-generation prototype iris identification system designed for stand-off cooperative access control. This system identifies individuals who stand in front of and face the system after 3.2 seconds on average. Subjects within a capture zone are imaged with a calibrated pair of wide-field-of-view surveillance cameras. A subject is located in three dimensions using face detection and triangulation. A zoomed near infrared iris camera on a pan-tilt platform is then targeted to the subject. The iris camera lens has its focal distance automatically adjusted based on the subject distance. Integrated with the iris camera on the pan-tilt platform is a near infrared illuminator that is composed of an array of directed LEDs. Video frames from the iris camera are processed to detect and segment the iris, generate a template and then identify the subject.

3D to 2D fingerprints: Unrolling and distortion correction

Touchless 3D fingerprint sensors can capture both 3D depth information and albedo images of the finger surface. Compared with 2D fingerprint images acquired by traditional contact-based fingerprint sensors, the 3D fingerprints are generally free from the distortion caused by non-uniform pressure and undesirable motion of the finger. Several unrolling algorithms have been proposed for virtual rolling of 3D fingerprints to obtain 2D equivalent fingerprints, so that they can be matched with the legacy 2D fingerprint databases. However, available unrolling algorithms do not consider the impact of distortion that is typically present in the legacy 2D fingerprint images. In this paper, we conduct a comparative study of representative unrolling algorithms and propose an effective approach to incorporate distortion into the unrolling process. The 3D fingerprint database was acquired by using a 3D fingerprint sensor being developed by the General Electric Global Research. By matching the 2D equivalent fingerprints with the corresponding 2D fingerprints collected with a commercial contact-based fingerprint sensor, we show that the compatibility between the 2D unrolled fingerprints and the traditional contact-based 2D fingerprints is improved after incorporating the distortion into the unrolling process.

Mobile, contactless, single-shot, fingerprint capture system

In some applications such as field stations, disaster situations or similar conditions, it is desirable to have a contactless, rugged means to collect fingerprint information. The approach described in this paper enables acceleration of the capture process by eliminating an otherwise system and finger cleanup procedure, minimizes the chance of the spread of disease or contaminations, and uses an innovative optical system able to provide rolled equivalent fingerprint information desirable for reliable 2D matching against existing databases. The approach described captures highresolution fingerprints and 3D information simultaneously using a single camera. Liquid crystal polarization rotators combined with birefringent elements provides the focus shift and a depth from focus algorithm extracts the 3D data. This imaging technique does not involve any moving parts, thus reducing cost and complexity of the system as well as increasing its robustness. Data collection is expected to take less than 100 milliseconds, capturing all four-finger images simultaneously to avoid sequencing errors. This paper describes the various options considered for contactless fingerprint capture, and why the particular approach was ultimately chosen.

Application issues in the use of depth from (de)focus analysis methods

Recovering 3D object information through analyzing image focus (or defocus) has been shown to be a potential tool in situations where only a single viewing point is possible. Precise modeling and manipulation of imaging system parameters, e.g. depth of field, modulation transfer function and sensor characteristics, as well as lighting condition and object surface characteristics are critical for effectiveness of such methods. Sub-optimal performance is achieved when one or more of these parameters are dictated by other factors. In this paper, we will discuss the implicit requirements imposed by most common depth from focus/defocus (DFF/DFD) analysis methods and offer related application considerations. We also describe how a priori information about the objects of interest can be used to improve performance in realistic applications of this technology.

3D imaging system for biometric applications

There is a growing interest in the use of 3D data for many new applications beyond traditional metrology areas. In particular, using 3D data to obtain shape information of both people and objects for applications ranging from identification to game inputs does not require high degrees of calibration or resolutions in the tens of micron range, but does require a means to quickly and robustly collect data in the millimeter range. Systems using methods such as structured light or stereo have seen wide use in measurements, but due to the use of a triangulation angle, and thus the need for a separated second viewpoint, may not be practical for looking at a subject 10 meters away. Even when working close to a subject, such as capturing hands or fingers, the triangulation angle causes occlusions, shadows, and a physically large system that may get in the way. This paper will describe methods to collect medium resolution 3D data, plus highresolution 2D images, using a line of sight approach. The methods use no moving parts and as such are robust to movement (for portability), reliable, and potentially very fast at capturing 3D data. This paper will describe the optical methods considered, variations on these methods, and present experimental data obtained with the approach.

Three-dimensional embedded defect detection and localization in a semi-transparent medium

The fabrication of new optical materials has many challenges that suggest the need for new metrology tools. To this purpose, the authors designed a system for localizing 10 micron embedded defects in a 10-millimeter thick semitransparent medium. The system, comprising a single camera and a motion system, uses a combination of brightfield and darkfield illumination. This paper describes the optical design and algorithm tradeoffs used to reach the desired detection and measurement characteristics using stereo photogrammetry and parallel-camera stereoscopic matching. Initial experiment results concerning defect detection and positioning, as well as analysis of computational complexity of a complete wafer inspection are presented. We concluded that parallel camera stereoscopic matching combined with darkfield illumination provides the most compatible solution to the 3D defect detection and positioning requirement, detecting 10 micron defects at a positioning accuracy of better than +/- 0.5 millimeters and at a speed of less than 3 minutes per part.

A hand-held triangulation sensor for small features measurement

This paper describes progressive generations of hand held triangulation sensors for measuring small features, from edge breaks to corrosion pits. We describe the design considerations, ergonomics, packaging and interface between the device and part, such as the sensor tip and optional fixtures. We then present a customized design to address different types of surface features and defects. Next, we present the calibration concept, and its execution. The paper closes by summarizing system performance evaluation experiments and their results. It was shown that the system is capable of measuring edges down to a radius of 250 microns at a repeatability of 50 microns.

Real-time 3D part metrology using polarization rotation

This paper describes a real time, low cost part metrology method for capturing and extracting 3D part data using a single camera and no moving elements. 3D capture in machine vision is typically done using stereo photogrammetry, phase shifting using structured light, or autofocus mechanism for depth capture. These methods rely on expensive and often slow components such as multiple cameras, specialized lighting, or motion components such as motors or piezoelectric actuators. We demonstrated a method for 3D capture using only a single camera, birefringent lenses and ultra-fast electronic polarization switches. Using multiple images acquired at different polarization states and thus different focal distances, a high-resolution 3D point cloud of a test part was extracted with a good match to the ground truth data. This paper will describe the operation of the method and discuss the practical limitations.

A single lens with no moving parts for rapid high-resolution 3D image capture

There are many visual inspection and sensing applications where both a high resolution image and a depth-map of the imaged object are desirable at high speed. Presently available methods to capture 3D data (stereo cameras and structured illumination), are limited in speed, complexity, and transverse resolution. Additionally these techniques rely on a separated baseline for triangulation, precluding use in confined spaces. Typically, off the shelf lenses are implemented where performance in resolution, field-of-view, and depth of field are sacrificed in order to achieve a useful balance. Here we present a novel lens system with high-resolution and wide field-of-view for rapid 3D image capture. The design achieves this using a single lens with no moving parts. A depth-from-defocus algorithm is implemented to reconstruct 3D object point clouds and matched with a fused image to create a 3D rendered view.

LED eye safety considerations in the design of iris capture systems

We have developed a standoff iris biometrics system for improved usability in access-control applications. The system employs an eye illuminator, which is composed of an array of encapsulated near-infrared light emitting diodes (NIRLEDs), which are triggered at the camera frame rate for reduced motion blur and ambient light effects. Neither the standards / recommendations for NIR laser and lamp safety, nor the LED-specific literature address all the specific aspects of LED eye-safety measurement. Therefore, we established exposure limit criteria based on a worst-case scenario combining the following: the CIE/ANSI standard/recommendations for exposure limits; concepts for maximum irradiance level and for strobing from the laser safety standards; and ad-hoc rules minimizing irradiance on the fovea, for handling LED arrays, and for LED mounting density. Although our system was determined as eye safe, future variants may require higher exposure levels and lower safety margins. We therefore discuss system configuration for accurate LED radiometric measurement that will ensure reliable eye-safety evaluation. The considerations and ad hoc rules described in this paper are not, and should not be treated as safety recommendations.