Test Methods to Rigorously, Reproducibly, and Accurately Measure the Detection Performance of Walk-through Metal Detectors.

Walk-through metal detectors (WTMDs) are the primary tool for the detection of concealed metal contraband and threat items on a person. They are found at almost all security checkpoint stations worldwide. It is important for security that assessing the detection performance of WTMDs is done rigorously, accurately, and reproducibly. Current standardized test methods do not provide this capability. Moreover, exhaustive testing would be prohibitively expensive and slow. Test methods, test objects, and their rationale are described here that can be used to accurately and reproducibly measure the detection performance of a WTMD while rigorously exercising its detection capability. Focused selection of the most informative test parameters reduces the time required for testing by about two orders of magnitude.

Predicting Detection Performance on Security X-Ray Images as a Function of Image Quality.

Developing methods to predict how image quality affects the task performance is a topic of great interest in many applications. While such studies have been performed in the medical imaging community, little work has been reported in the security X-ray imaging literature. In this paper, we develop models that predict the effect of image quality on the detection of the improvised explosive device components by bomb technicians in images taken using portable X-ray systems. Using a newly developed NIST-LIVE X-Ray Task Performance Database, we created a set of objective algorithms that predict bomb technician detection performance based on the measures of image quality. Our basic measures are traditional image quality indicators (IQIs) and perceptually relevant natural scene statistics (NSS)-based measures that have been extensively used in visible light image quality prediction algorithms. We show that these measures are able to quantify the perceptual severity of degradations and can predict the performance of expert bomb technicians in identifying threats. Combining NSS- and IQI-based measures yields even better task performance prediction than either of these methods independently. We also developed a new suite of statistical task prediction models that we refer to as quality inspectors of X-ray images (QUIX); we believe this is the first NSS-based model for security X-ray images. We also show that QUIX can be used to reliably predict conventional IQI metric values on the distorted X-ray images.

The IEEE TC-10 Standards: Update 2019.

There is a global need to standardize the terms and the test and computational methods that are used to describe and/or measure the parameters that characterize and define the performance of devices that generate signals and subsequently measure and analyze the waveforms acquired of those signals. This standardization is essential for accurate, reproducible, reliable, and communicable characterization of the performance of these devices, which supports technology and product advancement, product comparison and performance tracking, and device calibration and traceability. Users of the devices need to unambiguously specify the device performance required for particular applications. Manufacturers need to unambiguously state the performance of their devices (e.g., instruments, components, etc.). Metrology facilities need to perform calibrations with well-defined methods to produce reliable data expressed in clear terms. Measurement instruments need to acquire data with well-defined methods and present their results clearly. Technical Committee 10 (TC-10), the Waveform Generation, Measurement, and Analysis Committee of the IEEE Instrumentation and Measurement (I&M) Society, develops documentary standards to address these needs. The TC-10 comprises an international group of electronics engineers, mathematicians, professors and physicists with representatives from national metrology laboratories, national science laboratories, component manufacturers, the test instrumentation industry, academia, and end users. The published standards developed and maintained by the TC10 include: IEEE Std 181-2011, "Standard on Transitions, Pulses, and Related Waveforms;" IEEE Std 1057-2017, "Standard for Digitizing Waveform Recorders;" IEEE Std 1241-2010, "Standard for Terminology and Test Methods for Analog-to-Digital Converters;" IEEE Std 1658-2011, "Standard for Terminology and Test Methods for Digital-to-Analog Converters;" and the IEEE Std 1696-2013, "Standard for Terminology and Test Methods for Circuit Probes." In development is the IEEE Draft Std. P2414 "Draft Standard for Jitter and Phase Noise." The status of these standards are described herein.

Multivariate Statistical Approach to Image Quality Tasks.

Many existing Natural Scene Statistics-based no reference image quality assessment (NR IQA) algorithms employ univariate parametric distributions to capture the statistical inconsistencies of bandpass distorted image coefficients. Here we propose a multivariate model of natural image coefficients expressed in the bandpass spatial domain that has the potential to capture higher-order correlations that may be induced by the presence of distortions. We analyze how the parameters of the multivariate model are affected by different distortion types, and we show their ability to capture distortion-sensitive image quality information. We also demonstrate the violation of Gaussianity assumptions that occur when locally estimating the energies of distorted image coefficients. Thus we propose a generalized Gaussian-based local contrast estimator as a way to implement non-linear local gain control, that facilitates the accurate modeling of both pristine and distorted images. We integrate the novel approach of generalized contrast normalization with multivariate modeling of bandpass image coefficients into a holistic NR IQA model, which we refer to as multivariate generalized contrast normalization (MVGCN). We demonstrate the improved performance of MVGCN on quality relevant tasks on multiple imaging modalities, including visible light image quality prediction and task success prediction on distorted X-ray images.

Improved Threat Identification Using Tonemapping of High-Dynamic-Range X-ray Images.

Transmission X-ray systems are used to image the contents of suspicious packages, luggage, and cargo. The images can have a dynamic range of 1,000:1 or greater, but are typically displayed on consumer-grade displays with a low-dynamic range of less than 255:1. We show that modern tonemapping algorithms can greatly improve the process of displaying X-ray images on low-dynamic-range displays and compare the performance of some popular algorithms for this purpose.

Testing the Image Quality of Cabinet X-ray Systems for Security Screening: The Revised ASTM F792 Standard.

ASTM F792, Standard Practice for Evaluating the Imaging Performance of Security X-ray Systems, provides test objects and methods for measuring the imaging performance of cabinet X-ray systems used at security checkpoints. The standard is widely used, with many thousands of ASTM F792 test objects utilized throughout the world. The last major revision of the standard was more than 15 years ago (2001), and since that time, several deficiencies have been noted when using the standard for testing modern systems employing multiple-view and multiple-energy configurations. Accordingly, the present work describes a new revision of the ASTM F792 standard realized as a trifurcation into three parts, each with its own separate test object and associated test method. The three parts of the standard are intended for routine testing, human-perception testing, and objective technical testing, and represent a major update to this venerable standard.

Method for Measuring the Phase Spectrum of the Output of a Frequency Source Used in the Calibration of an Electroshock Weapon Characterization System.

Electroshock weapons (ESWs) output a transient burst of impulse-like high-voltage electrical signals that can incapacitate a human target. To ensure safe and effective operation of ESW, their outputs must be accurately measured. Accordingly, the systems used to measure the output of an ESW must be accurately characterized, and their response functions must be known for subsequent processing of the ESW output waveforms (current and high voltage). The long epochs (> 5 s) and high-bandwidth frequency content (> 200 MHz) of the ESW output require unique measurement instrumentation and calibration tools. A frequency-domain swept-frequency method is proposed here for the calibration of the phase response of an ESW measurement system. This method, although motivated by the ESW measurement application, is also applicable to other systems.

Tasking on Natural Statistics of Infrared Images.

Natural scene statistics (NSSs) provide powerful, perceptually relevant tools that have been successfully used for image quality analysis of visible light images. Since NSS capture statistical regularities that arise from the physical world, they are relevant to long wave infrared (LWIR) images, which differ from visible light images mainly by the wavelengths captured at the imaging sensors. We show that NSS models of bandpass LWIR images are similar to those of visible light images, but with different parameterizations. Using this difference, we exploit the power of NSS to successfully distinguish between LWIR images and visible light images. In addition, we study distortions unique to LWIR and find directional models useful for detecting the halo effect, simple bandpass models useful for detecting hotspots, and combinations of these models useful for measuring the degree of non-uniformity present in many LWIR images. For local distortion identification and measurement, we also describe a method for generating distortion maps using NSS features. To facilitate our evaluation, we analyze the NSS of LWIR images under pristine and distorted conditions, using four databases, each captured with a different IR camera. Predicting human performance for assessing distortion and quality in LWIR images is critical for task efficacy. We find that NSS features improve human targeting task performance prediction. Furthermore, we conducted a human study on the perceptual quality of noise-and blur-distorted LWIR images and create a new blind image quality predictor for IR images.

Test Object for Accurate and Reproducible Measurement of the Detection Response of Hand-worn and Hand-held Metal Detectors.

The assessment of the detection performance of metal detectors (hand-worn, hand-held, and walk-through models) is based on the ability of the detectors to sound an alarm when presented with a test object. These test objects are typically actual threat items or simulated threat items. The orientation of these test objects with the magnetic field generated by the metal detectors may affect the detectability of the test objects. More importantly, small misorientations of a threat object or simulated threat object may cause the operator to incorrectly attribute to the metal detector a higher performance than it is capable of providing. Consequently, to support accurate and reproducible characterization of the performance of a metal detector, orientation effects should be minimized or eliminated. We discuss the use of spherical test objects to eliminate this potentially serious error in the assessment of the detection performance of a metal detector. In this study, we consider only hand-worn and hand-held metal detectors because of their similarity in size and operation.

Calibration of Speed Enforcement Down-The-Road Radars.

We examine the measurement uncertainty associated with different methods of calibrating the ubiquitous down-the-road (DTR) radar used in speed enforcement. These calibration methods include the use of audio frequency sources, tuning forks, a fifth wheel attached to the rear of the vehicle with the radar unit, and the speedometer of the vehicle. We also provide an analysis showing the effect of calibration uncertainty on DTR-radar speed measurement uncertainty.

Nanosecond delay with subpicosecond uncertainty.

We have combined a commercially available, variable-length coaxial delay line (trombone line) with a high-resolution linear translation system. The result is better resolution and lower uncertainty in the achievable delays than previously available. The range of delay is 0 ps to approximately 1250 ps, the bidirectional resolution is 2.0 ps, the unidirectional resolution is 0.2 ps, and the uncertainty (95% confidence interval) in the measured delay is +/-0.09 ps. Drift, temperature dependence, repeatability, linearity, and hysteresis were also examined.