BiDi screen: a thin, depth-sensing LCD for 3D interaction using light fields

We transform an LCD into a display that supports both 2D multi-touch and unencumbered 3D gestures. Our BiDirectional (BiDi) screen, capable of both image capture and display, is inspired by emerging LCDs that use embedded optical sensors to detect multiple points of contact. Our key contribution is to exploit the spatial light modulation capability of LCDs to allow lensless imaging without interfering with display functionality. We switch between a display mode showing traditional graphics and a capture mode in which the backlight is disabled and the LCD displays a pinhole array or an equivalent tiled-broadband code. A large-format image sensor is placed slightly behind the liquid crystal layer. Together, the image sensor and LCD form a mask-based light field camera, capturing an array of images equivalent to that produced by a camera array spanning the display surface. The recovered multi-view orthographic imagery is used to passively estimate the depth of scene points. Two motivating applications are described: a hybrid touch plus gesture interaction and a light-gun mode for interacting with external light-emitting widgets. We show a working prototype that simulates the image sensor with a camera and diffuser, allowing interaction up to 50 cm in front of a modified 20.1 inch LCD.National Science Foundation (U.S.) (Grant CCF-0729126)Alfred P. Sloan Foundatio

Coded-aperture imaging systems:past, present and future development - a review

Scintillator based coded-aperture imaging has proven to be effective when applied for X- and gamma-ray detection. Adaptation of the same method for neutron imaging has resulted in a number of propitious systems, which could be potentially employed for neutron detection in security and nuclear decommissioning applications. Recently developed scintillator based coded-aperture imagers reveal that localisation of neutron sources using this technique may be feasible, since pulse shape discrimination algorithms implemented in the digital domain can reliably separate gamma-rays from fast neutron interactions occurring within an organic scintillator. Moreover, recent advancements in the development of solid organic scintillators make them a viable solution for nuclear decommissioning applications as they present less hazardous characteristics than currently dominating liquid scintillation detectors. In this paper existing applications of coded-apertures for radiation detection are critically reviewed, highlighting potential improvements for coded-aperture based neutron source localisation. Further, the suitability of coded-apertures for neutron imaging in nuclear decommissioning is also assessed using Monte-Carlo modelling

BiDi screen : depth and lighting aware interaction and display

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 75-79).In this thesis, I describe a new type of interactive display that supports both on-screen multi-touch interactions and off-screen hover-based gestures. This BiDirectional (BiDi) screen, capable of both image capture and display, is inspired by emerging LCDs that use embedded optical sensors to detect multiple points of direct contact. The key contribution of this thesis is to exploit the spatial light modulation capability of LCDs to allow dynamic mask-based scene capture without interfering with display functionality. A large-format image sensor is placed slightly behind the liquid crystal layer. By alternatly switching the liquid crystal between a display mode showing traditional graphics and a capture mode in which the backlight is disabled and a pinhole array or an equivalent tiled-broadband code is displayed, the BiDi Screen can recover multi-view orthographic imagery while functioning as a 2D display. The recovered imagery is used to passively estimate the depth of scene points from focus. I discuss the design and construction of a prototype to demonstrate these capabilities in two motivating applications: a hybrid touch plus gesture interaction and a light-gun mode for interacting with external light-emitting widgets. The working prototype simulates the large format light sensor with a camera and diffuser, supporting interaction up to 50 cm in front of a modified 20.1 inch LCD.by Matthew W. Hirsch.S.M

The development of x-ray backscatter imaging systema through simulation

X-ray backscatter has applications in defence and security, medical imaging, astrophysics and industry. The development and testing of X-ray backscatter imaging systems can be achieved not only by experiment, but also by using Monte-Carlo modelling. The PENELOPE simulation package was chosen for its versatility and transparency. However, PENELOPE is a radiation transport package that is not user-friendly, is not inherently compatible with parallel processing, and is not equipped with the facility to process output data in a way that replicates the output from imaging plates or energy dispersive detectors. Tools called PENMAT and PAXI were written in MATLAB to extend the capability of PENELOPE and so enable the efficient exploration of X-ray backscatter imaging which is the focus of this study. The enhanced PENELOPE suite was used to model a real thermionic source to validate the process by comparison with experiment, and model virtual sources suitable for exploring fundamental principles of backscatter. Virtual sources were conceived and designed to efficiently characterise various imaging system features. These include mono-directional and mono-energetic sources (to isolate energy dependant scattering cross sections), flat spectrum sources (to objectively characterise transmission through mask materials) and thin ‘wire form’ sources (to simultaneously characterise the spatial resolution and field of view of X-ray optics). A process of using virtual detectors to feed the input of virtual sources was used to shortcut the repeated computationally expensive modelling of a thermionic tube. With this efficient process and parallel computing, various combinations of pinhole and Coded Aperture optics could be efficiently tested and compared. To enable systematic comparisons the image quality metrics of signal, noise, contrast, resolution, field of view etc. are identified and procedures developed to extract them from images. ii For the experimental energy range of likely practical use, it was found that pure tungsten masks were superior to other alloys studied and that a 2mm pinhole gave the most generally suitable resolution/signal compromise. The results were consistent with physical experiment. A range of Coded Apertures were also modelled and compared favourably to experiment. The pinhole work on field of view informs the envelope within which coded apertures could avoid partial coding. The HEXITEC energy dispersive image plate was used to collect experimental images from a multi material quadrant. The image was simulated accurately using PAXI. Further, modelling with PAXI allowed the distinct interaction processes giving rise to image characteristics to be isolated. This concept was extended with a unique and innovative 2π hemispherical detector, which efficiently captured backscatter X-rays from carbon, copper, manganese dioxide, and lead when shielded and unshielded. This process allowed the brightness of materials to be studied, as governed by the complex combination of attenuation and cross section with angle. Further, the relative contributions from Compton, elastic and fluorescent processes to image brightness and spectral features could be isolated and compared with angle. This was conducted with/without shielding. This cannot be achieved by experiment, and pilots how modelling can inform the best beam energies and detector angles where the backscatter X-rays contain the right information to characterise materials and structures. This work includes significant use of simulation and also a strong supporting element of physical experimentation. The development of modelling techniques and their exploitation can give information that physical experiment cannot, whilst experimentation has been shown to validate the use of simulation and identify some limitation

A Compact Neutron Scatter Camera Using Optical Coded-Aperture Imaging

The detection and localization of fast neutron resources is an important capability for a number of nuclear security areas such as emergency response and arms control treaty verification. Neutron scatter cameras are one technology that can be used to accomplish this task, but current instruments tend to be large (meter scale) and not portable. Using optical coded-aperture imaging, fast plastic scintillator, and fast photodetectors that were sensitive to single photons, a portable neutron scatter camera was designed and simulated. The design was optimized, an experimental prototype was constructed, and neutron imaging was demonstrated with a tagged 252Cf source in the lab

Development of scintillator based coded-aperture neutron imager for nuclear decommissioning

This thesis documents a proof-of-concept study of a novel, scintillator based, coded-aperture approach to neutron detection. Developments presented in this document suggest that coded-aperture approach, previously mainly associated with photon detectors, can be adapted for a small scale neutron detector. This work represents an innovative, scintillator based approach for small scale radiation detector aimed at nuclear decommissioning applications. A novel pixelated plastic scintillator was designed and built in this work. Scintillator cells 2.8 x 2.8 x 15 mm each), build of EJ-299-34 plastic were manufactured and arranged into a 13 x 13 array. The plastic scintillator which was used in this research was sensitive to both gamma and neutron fields. Experimental data were obtained for various solid scintillator samples and a comparison of a number of pulse shape discrimination techniques was performed. Prior to the experimental work, a simulation based study identified potential candidates for the scintillation material, as well as characterised the mixed-field environment, provided by 252Cf at Lancaster University, UK. Suitable coded-aperture materials were also computationally identified, and were subsequently used to manufacture a tungsten coded aperture, based on modified uniformly redundant array design technique. Pixelated nature of the coded-aperture based approach to radiation imaging allows the lateral resolution of the image to be improved, without affecting the signal-to-noise ratio. The focal point of this technique is located in the coded-aperture design and the scintillator. Modulation properties of the rank-7 coded aperture, made of tungsten using additive manufacturing techniques, were investigated. The experiment was performed using 137Cs gamma-ray calibration source at Lancaster University. Data obtained were subsequently used to perform the localisation of the point source used in this study. The idea of using tungsten coded aperture for dual-particle imaging was also simulated using Monte Carlo techniques (MCNPX) prior to the experimental work. The pulse shape discrimination performance of the pixelated organic plastic scintillator was investigated. The scintillator was exposed to a mixed-field environment provided by 252Cf and its performance was compared to that of a cylindrical plastic sample. Tests were also carried out in moderated neutron and gamma-ray fields of 252Cf. Suitable pixelated photodetectors, together with associated readout electronics circuitry, were also identified

Study of the tracking performance of a liquid Argon detector based on a novel optical imaging concept

The Deep Underground Neutrino Experiment (DUNE) is a long-baseline accelerator experiment designed to make a significant contribution to the study of neutrino oscillations with unprecedented sensitivity. The main goal of DUNE is the determination of the neutrino mass ordering and the leptonic CP violation phase, key parameters of the three-neutrino flavor mixing that have yet to be determined. An important component of the DUNE Near Detector complex is the System for on-Axis Neutrino Detection (SAND) apparatus, which will include GRAIN (GRanular Argon for Interactions of Neutrinos), a novel liquid Argon detector aimed at imaging neutrino interactions using only scintillation light. For this purpose, an innovative optical readout system based on Coded Aperture Masks is investigated. This dissertation aims to demonstrate the feasibility of reconstructing particle tracks and the topology of CCQE (Charged Current Quasi Elastic) neutrino events in GRAIN with such a technique. To this end, the development and implementation of a reconstruction algorithm based on Maximum Likelihood Expectation Maximization was carried out to directly obtain a three-dimensional distribution proportional to the energy deposited by charged particles crossing the LAr volume. This study includes the evaluation of the design of several camera configurations and the simulation of a multi-camera optical system in GRAIN

Microoptical multi aperture imaging systems

Die Verkleinerung digitaler Einzelapertur-Abbildungssysteme erreicht aktuell physikalische sowie technische Limits. Die Miniaturisierung führt zu einer Verringerung sowohl des Auflösungsvermögens als auch des Signal-Rausch-Verhältnisses. Einen Ausweg zeigen die Prinzipien der kleinsten in der Natur bekannten Sehsysteme - die Facettenaugen. Die parallelisierte Anordnung einer großen Anzahl von Optiken ermöglicht, trotz der geringen Baugröße, eine große Informationsmenge aus einem ausgedehnten Gesichtsfeld zu übertragen. Ziel ist es, die Vorteile natürlicher Facettenaugen zu analysieren und diese zur Überwindung aktueller Grenzen der Miniaturisierung von digitalen Kameras zu adaptieren. Durch die Synergie von Optik, Opto-Elektronik und Bildverarbeitung wird die Miniaturisierung unter Erreichung praxisrelevanter Parameter angestrebt. Dafür wurde eine systematische Einteilung bereits bekannter und neuartiger Prinzipien von Multiapertur-Abbildungssystemen vorgenommen. Das grundlegende Verständnis der Vor- und Nachteile sowie des Skalierungsverhaltens der verschiedenen Ansätze ermöglichte die detaillierte Untersuchung der zwei erfolgversprechendsten Systemklassen. Für die Auslegung der Multiapertur-Optiken wurde eine Kombination aus Ansätzen des klassischen Optikdesigns und neuen semi-automatisierten Simulations- und Optimierungsmethoden mittels Ray-Tracing angewandt. Die mit natürlichen Facettenaugen vergleichbare Größe der Optiken ermöglichte die Verwendung mikrooptischer Herstellungsverfahren im Wafermaßstab. Es wurden Prototypen experimentell untersucht und die simulierten Systemparameter mit Hilfe der für die Multiapertur Anordnungen angepassten Messmethoden bestätigt. Die dargestellten Lösungen demonstrieren grundsätzlich neue Ansätze für den Bereich der hochauflösenden, miniaturisierten Abbildungsoptik, die kleinste Baulängen bei gegebenem Auflösungsvermögen erzielen. Somit sind sie im Stande die Skalierungslimits der Einzelapertur-Abbildungsoptik zu überwinden

Microoptical multi aperture imaging systems

Die Verkleinerung digitaler Einzelapertur-Abbildungssysteme erreicht aktuell physikalische sowie technische Limits. Die Miniaturisierung führt zu einer Verringerung sowohl des Auflösungsvermögens als auch des Signal-Rausch-Verhältnisses. Einen Ausweg zeigen die Prinzipien der kleinsten in der Natur bekannten Sehsysteme - die Facettenaugen. Die parallelisierte Anordnung einer großen Anzahl von Optiken ermöglicht, trotz der geringen Baugröße, eine große Informationsmenge aus einem ausgedehnten Gesichtsfeld zu übertragen. Ziel ist es, die Vorteile natürlicher Facettenaugen zu analysieren und diese zur Überwindung aktueller Grenzen der Miniaturisierung von digitalen Kameras zu adaptieren. Durch die Synergie von Optik, Opto-Elektronik und Bildverarbeitung wird die Miniaturisierung unter Erreichung praxisrelevanter Parameter angestrebt. Dafür wurde eine systematische Einteilung bereits bekannter und neuartiger Prinzipien von Multiapertur-Abbildungssystemen vorgenommen. Das grundlegende Verständnis der Vor- und Nachteile sowie des Skalierungsverhaltens der verschiedenen Ansätze ermöglichte die detaillierte Untersuchung der zwei erfolgversprechendsten Systemklassen. Für die Auslegung der Multiapertur-Optiken wurde eine Kombination aus Ansätzen des klassischen Optikdesigns und neuen semi-automatisierten Simulations- und Optimierungsmethoden mittels Ray-Tracing angewandt. Die mit natürlichen Facettenaugen vergleichbare Größe der Optiken ermöglichte die Verwendung mikrooptischer Herstellungsverfahren im Wafermaßstab. Es wurden Prototypen experimentell untersucht und die simulierten Systemparameter mit Hilfe der für die Multiapertur Anordnungen angepassten Messmethoden bestätigt. Die dargestellten Lösungen demonstrieren grundsätzlich neue Ansätze für den Bereich der hochauflösenden, miniaturisierten Abbildungsoptik, die kleinste Baulängen bei gegebenem Auflösungsvermögen erzielen. Somit sind sie im Stande die Skalierungslimits der Einzelapertur-Abbildungsoptik zu überwinden