Opaque Objects Research Articles

3D Surface reconstruction of transparent objects using laser scanning with LTFtF method

Three-dimensional (3D) vision plays an important role in robotics and industrial automation, wherein the reconstruction of transparent objects poses a great challenge. In this paper, we present a scheme for reconstructing the 3D surfaces of transparent objects based on a combination of stereo matching and laser scanning. The traditional laser scanning method can achieve good results in the 3D reconstruction of opaque objects. However, this method will fail for transparent and semitransparent objects because both the front and back surfaces of these objects will reflect the feature laser line. It is difficult to determine the reflection surface of the feature lines captured by the camera. To distinguish the laser reflected by the front surface from the distracting laser reflections by the other surfaces, a laser tracking frame to frame (LTFtF) method is proposed. The laser lines reflected from the front surface of the target are then reconstructed using stereo vision. The entire 3D surface is obtained through laser scanning. In addition, we improve the matching accuracy and point cloud density through an internal pixel matching method. Various experiments were conducted to verify the capability of the proposed method, which includes the reconstruction of transparent and semitransparent objects of various shapes. The proposed method was compared with traditional laser scanning algorithms.

High-speed laser speckle imaging to unravel picoliter drop-on-demand to substrate interaction.

Understanding phenomena such as evaporation and imbibition of picoliter droplets into porous substrates is crucial in printing industry to achieve a higher printing quality and print speed. After printing, the residual pigment must remain fixed at the desired location on a substrate and be of a desired volume to yield a high resolution and vibrantly printed page that has become the expectation of modern printing technology. Current research entails not only chemical composition of the ink but also how this links to the dynamics and interactions that occur between the ink and the substrate at every stage of the printed spot formation, including evaporation, wetting, and imbibition. In this paper, we present an instrument that can print on-demand picoliter volume droplets of ink onto substrates and then immediately record on evolution of the resulting dynamics when these two materials interact. This high-speed laser speckle imaging (HS-LSI) technique has been developed to monitor nanometer displacement of the drying and imbibing ink droplet at a high frame rate, up to 20000Hz, given the short timescales of these interactions. We present the design of the instrument, discuss the related challenges and the theory underlying the LSI technique, specifically how photons non-evasively probe opaque objects in a multiple scattering regime, and show how this technique can unravel the dynamics of drying and imbibition. We will finish giving a validation on the instrument and an example of its usage.

Versatile non-luminescent color palette based on guest exchange dynamics in paramagnetic cavitands

Multicolor luminescent portrayal of complexed arrays is indispensable for many aspects of science and technology. Nevertheless, challenges such as inaccessible readouts from opaque objects, a limited visible-light spectrum and restricted spectral resolution call for alternative approaches for multicolor representation. Here, we present a strategy for spatial COlor Display by Exploiting Host-guest Dynamics (CODE-HD), comprising a paramagnetic cavitand library and various guests. First, a set of lanthanide-cradled α-cyclodextrins (Ln-CDs) is designed to induce pseudo-contact shifts in the 19F-NMR spectrum of Ln-CD-bound guest. Then, capitalizing on reversible host-guest binding dynamics and using magnetization-transfer 19F-MRI, pseudo-colored maps of complexed arrays are acquired and applied in molecular-steganography scenarios, showing CODE-HD’s ability to generate versatile outputs for information encoding. By exploiting the widely shifted resonances induced by Ln-CDs, the guest versatility and supramolecular systems' reversibility, CODE-HD provides a switchable, polychromatic palette, as an advanced strategy for light-free, multicolor-mapping.

Do We Visually Experience Objects’ Occluded Parts?

AbstractA number of philosophers have held that we visually experience objects’ occluded parts, such as the out-of-view exterior of a voluminous, opaque object. That idea is supposed to be what best explains the fact that we see objects as whole or complete despite having only a part of them in view at any given moment. Yet, the claim doesn’t express a phenomenological datum and the reasons for thinking we do experience objects’ occluded parts, I argue, aren’t compelling. Additionally, I anticipate and reply to attempts to salvage the idea by appeal to perceptual expectation and amodal completion. Lastly, I address potential concerns that the only way to capture the phenomenal character of perceiving voluminous objects is to say experience outstrips what’s in view, providing a description of such experience without any implication of that idea.

Arrangement optimization of a novel three dimensional multiphase flow imaging device employing modified harmony search algorithm

Gas–liquid two-phase flow is a typical flow. Its bubble characteristic measurement is of great importance on studying the flow mechanism and guiding the practical fluid mechanical engineering. In this paper, a novel three dimensional (3D) multiphase flow imaging device was designed and optimized to measure the transparent object that has an opaque object in the center of the 3D observed area. Its mathematical model was built and the constraints were defined based on the geometrical relationship and design requirements. Based on the original harmony search (HS) algorithm, a modified harmony search algorithm (MHS-MC) for improving both the performance on the global optima of the multi-modal problems and the convergence performance of the constrained optimization problems was integrated and applied to optimize the arrangement of the single-camera-multi-mirror device. As a case study, the 3D multiphase flow imaging method was applied in the 3D reconstruction of the cavitation bubble cluster inside a water hydraulic valve. The statistics of the Pareto data show the good performance of the MHS-MC algorithm. And the cavitation experimental results testify the effectiveness of the proposed MHS-MC algorithm. The cavitation bubble cluster can be reconstructed with quite high precision.

Mail Inspection Based on Terahertz Time-Domain Spectroscopy

One of the most prominent applications of terahertz time-domain spectroscopy is the spectral investigation of materials covered by visibly opaque objects. Therefore, terahertz waves are well suited to inspect the content of mail. We report on our work on mail inspection in this spectral range including machine design, optical layouts, data analysis, and implementations.

Performance Analysis of Optimization Algorithms for a Cross-Layer Shadowing Recover Scheme

Optical attocell networks based on visible light communication (VLC) are cost-efficient solutions which complement the spectrum shortage of radio-frequency(RF)-based indoor wireless networks. However, communication using visible light is vulnerable to shadowing effect caused by random pedestrians as visible light cannot penetrate opaque objects. A cross-layer resilience scheme RASP (routing, load assignment, subcarrier selection, power allocation) is proposed to address the shadowing effect. Network performance using different combinations of cross-layer control policies, i.e., algorithms and allocation methods, is evaluated and compared by RASP. An optimization algorithm is used to find the optimal/near-optimal combination of RASP control policies. In order to find the proper optimization algorithm for RASP, we investigate and compare the performance of different algorithms, including partial enumeration and neighbor-searching algorithms like hill-climbing and Tabu-search. An improved Tabu-search algorithm is proposed to reduce the time-complexity.

Large volume holographic imaging for biological sample analysis.

.Significance: Particle field holography is a versatile technique to determine the size and distribution of moving or stationary particles in air or in a liquid without significant disturbance of the sample volume. Although this technique is applied in biological sample analysis, it is limited to small sample volumes, thus increasing the number of measurements per sample. In this work, we characterize the maximum achievable volume limit based on the specification of a given sensor to realize the development of a potentially low-cost, single-shot, large-volume holographic microscope.Aim: We present mathematical formulas that will aid in the design and development and improve the focusing speed for the numerical reconstruction of registered holograms in particle field holographic microscopes. Our proposed methodology has potential application in the detection of Schistosoma haematobium eggs in human urine samples.Approach: Using the Fraunhofer holography theory for opaque objects, we derived an exact formula for the maximum diffraction-limited volume for an in-line holographic setup. The proof-of-concept device built based on the derived formulas was experimentally validated with urine spiked with cultured Schistosoma haematobium eggs.Results: Results obtained show that for urine spiked with Schistosoma haematobium eggs, the volume thickness is limited to several millimeters due to scattering properties of the sample. The distances of the target particles could be estimated directly from the hologram fringes.Conclusion: The methodology proposed will aid in the development of large-volume holographic microscopes.

An impacted coin in the esophagus: a cause of dysphagia in a child.

A 4-year-old female with no previous medical history presented to the Emergency Department complaining of difficulty in swallowing especially solid food for a duration of 4 days. This was accompanied by some painful swallowing whenever she attempted taking solid foods. She preferred taking liquids in all the four days. She had no cough, difficulty in breathing, chest pain, stridor, drooling or fever. Physical examination revealed relatively normal oral, neck, abdominal, respiratory and neurological examination. An anteroposterior chest X-rays (A) revealed a round opaque object and a lateral neck X-ray(B) showed a thin opaque object, presenting in a coronal plane, on the same level of the child’s esophagus. Our patient was taken to the emergency operating theatre for endoscopic removal of an esophageal foreign body under anesthesia. A coin was removed without any complications. Initial use of X-ray investigations is important for children with dysphagia before opting for invasive procedures. A coin in the esophagus lies in the coronal view, whereas when situated in the trachea it lies in the sagittal view.

Glossy probe reprojection for interactive global illumination

Recent rendering advances dramatically reduce the cost of global illumination. But even with hardware acceleration, complex light paths with multiple glossy interactions are still expensive; our new algorithm stores these paths in precomputed light probes and reprojects them at runtime to provide interactivity. Combined with traditional light maps for diffuse lighting our approach interactively renders all light paths in static scenes with opaque objects. Naively reprojecting probes with glossy lighting is memory-intensive, requires efficient access to the correctly reflected radiance, and exhibits problems at occlusion boundaries in glossy reflections. Our solution addresses all these issues. To minimize memory, we introduce an adaptive light probe parameterization that allocates increased resolution for shinier surfaces and regions of higher geometric complexity. To efficiently sample glossy paths, our novel gathering algorithm reprojects probe texels in a view-dependent manner using efficient reflection estimation and a fast rasterization-based search. Naive probe reprojection often sharpens glossy reflections at occlusion boundaries, due to changes in parallax. To avoid this, we split the convolution induced by the BRDF into two steps: we precompute probes using a lower material roughness and apply an adaptive bilateral filter at runtime to reproduce the original surface roughness. Combining these elements, our algorithm interactively renders complex scenes while fitting in the memory, bandwidth, and computation constraints of current hardware.

Décrire et analyser la production des inégalités scolaires: l'apport de la sociologie de Basil Bernstein

Dès les années 90 le sociologue britannique Basil Bernstein reprochait aux travaux de Bourdieu et aux théories de la Reproduction (mais la question vaut d’être également posée à bien d’autres sociologies de l’éducation qui se posent en alternative à ces théories) de demeurer trop générales, de ne pas se soucier suffisamment de l’analyse interne des structures et modes de fonctionnement du champ éducatif, et de ne pouvoir ainsi « fournir des principes puissants de description des instances pédagogiques, de leurs discours, de leurs pratiques » (Bernstein, 2007, p. 26). De fait, à de rares exceptions près, la fonction de transmission du savoir et ses modalités pratiques apparaissent comme le parent pauvre de la sociologie de l'éducation : objet opaque et objet suspect, « mauvais objet », mystification, leurre derrière lesquels se cacheraient les « véritables fonctions » (reproduction sociale, aliénation, domestication...) de l'institution scolaire dont la sociologie aurait pour objet de rechercher et dévoiler les modes opératoires. Cette réticence est devenue un obstacle pour décrire et analyser, et donc pour contribuer à transformer, les processus concrets par lesquels se produisent, entre contextes et situations, les inégalités scolaires, de classe et de genre. Il nous faut au contraire pour cela savoir nouer des rapports renouvelés entre sociologie, psychologie culturelle et didactique. Nous montrerons, à partir d’exemples tirés d’observations prolongées de classes ordinaires, combien la théorie de Bernstein constitue un outil précieux pour construire un cadre conceptuel et des méthodologies empiriques au service de cet objectif.

Information for perceiving blurry events: Optic flow and color are additive.

Information used in visual event perception includes both static image structure projected from opaque object surfaces and dynamic optic flow generated by motion. Events presented in static blurry grayscale displays have been shown to be recognized only when and after presented with optic flow. In this study, we investigate the effects of optic flow and color on identifying blurry events by studying the identification accuracy and eye-movement patterns. Three types of color displays were tested: grayscale, original colors, or rearranged colors (where the RGB values of the original colors were adjusted). In each color condition, participants identified 12 blurry events in five experimental phases. In the first two phases, static blurry images were presented alone or sequentially with a motion mask between consecutive frames, and identification was poor. In Phase 3, where optic flow was added, identification was comparably good. In Phases 4 and 5, motion was removed, but identification remained good. Thus, optic flow improved event identification during and after its presentation. Color also improved performance, where participants were consistently better at identifying color displays than grayscale or rearranged color displays. Importantly, the effects of optic flow and color were additive. Finally, in both motion and postmotion phases, a significant portion of eye fixations fell in strong optic flow areas, suggesting that participants continued to look where flow was available even after it stopped. We infer that optic flow specified depth structure in the blurry image structure and yielded an improvement in identification from static blurry images.

Spatial ultrasound modulation by digitally controlling microbubble arrays

Acoustic waves, capable of transmitting through optically opaque objects, have been widely used in biomedical imaging, industrial sensing and particle manipulation. High-fidelity wave front shaping is essential to further improve performance in these applications. An acoustic analog to the successful spatial light modulator (SLM) in optics would be highly desirable. To date there have been no techniques shown that provide effective and dynamic modulation of a sound wave and which also support scale-up to a high number of individually addressable pixels. In the present study, we introduce a dynamic spatial ultrasound modulator (SUM), which dynamically reshapes incident plane waves into complex acoustic images. Its transmission function is set with a digitally generated pattern of microbubbles controlled by a complementary metal–oxide–semiconductor (CMOS) chip, which results in a binary amplitude acoustic hologram. We employ this device to project sequentially changing acoustic images and demonstrate the first dynamic parallel assembly of microparticles using a SUM.

Full-view three-dimensional shape parameters measurement and visualization with logic optical projection tomography

We propose a logic optical projection tomography (LOPT) method to realize full-view, three-dimensional (3-D) shape parameters measurement and visualization for opaque objects. The main innovation of LOPT is use of a logic process to obtain high-contrast and homogeneous boundary projection signals. According to the reconstructed 2-D cross-section images, the structure characteristic points in each slice are independently extracted and combined to produce a full-view 3-D image. Further, the structural shape parameters of individual parts of object such as the inscribed cylinder, center line, and double threads are obtained and visualized simultaneously. Our experimental results demonstrate that LOPT can be potentially developed as an economical optical measurement and visualization tool for some industrial application.

Detecting Delaminations in Semitransparent Glass Fiber Composite by Using Pulsed Infrared Thermography

Thanks to its good strength/mass ratio, a glass fibre reinforced plastic (GFRP) composite is a common material widely used in aviation, power production, automotive and other industries. In its turn, active infrared (IR) nondestructive testing (NDT) is a common inspection technique for detecting and characterizing structural defects in GFRP. Materials to be tested are typically subjected to optical heating which is supposed to occur on the material surface. However, GFRP composite is semi-transparent for optical radiation of both visual and IR spectral bands. Correspondingly, the inspection process represents a certain combination of both optical and thermal phenomena. Therefore, the known characterization algorithms based on pure heat diffusion cannot be applied to semi-transparent materials. In this study, the phenomenon of GFRP semi-transparency has been investigated numerically and experimentally in application to thermal NDT. Both Xenon flash tubes and a laser have been used for thermal stimulation of opaque and semi-transparent test objects. It has been shown that the penetration of optical heating radiation into composite reduces detectability of shallower defects, and the signal-to-noise ratio can be enhanced by applying the technique of thermographic signal reconstruction (TSR). In the inspection of the semi-transparent GFRP composite, the most efficient has been the laser heating followed by the TSR data processing. The perspectives of defect characterization of semi-transparent materials by using laser heating are discussed. A neural network has been used as a candidate tool for evaluating defect depth in composite materials, but its training should be performed in identical with testing conditions.

Method of Multi-Angle Transmission Radiowave Tomography of Dielectric Objects

A method for solving the inverse problem for reconstructing the spatial distribution of dielectric permittivity from the results of multi-angle transmission broadband radiosounding is proposed. The method is based on inverse wave propagation. The average refractive index of the medium along the wave trajectory is calculated by comparing the results of the calculation of the time delay of the inverse signal in the entire sounding region and the forward propagation time in a homogeneous medium. This method takes into account diffraction effects in solving a direct problem, which allows one to obtain a resolution in the order of a wavelength. The combination of time delays obtained at different probing angles allows the restoration of the distribution of the refractive index in the medium. The paper presents the results of the numerical simulation of this method. The novelty of the proposed approach compared to the conventional back-projection algorithm is that ray approximation is not applied. Instead of the absorption coefficient (used in X-ray tomography), a time delay is considered, which is restored in the entire probed region. The developed method can be widely used in radiowave tomography or microwave tomography for remote non-destructive testing, diagnostics for the internal structures of inhomogeneous media and the restoration of the shapes of opaque objects based on multisensor sensing.

An Efficient Way to Detect and Remove Shadows Based on Multiple Light Sources

A shadow is shaped when a light is blocked by an opaque object. They are sometimes unwanted as they may cause failure of image analysis and can also cause poor eminence of information. This paper first describes some important techniques that are used for shadow detection such as segmentation, Histogram Matching and some techniques that are used for shadow removal such as Morphological operations. The proposed methodology is to design a system based on three basic aims-the first goal is shadow detection of single and multiple images, second goal is to remove the shadow from the single and multiple images and third is to calculate the different parameter for measuring the quality of shadow removal method. Once the shadows are detected it becomes simple to detect a non shadow area which is estimated using morphological operators but sometimes when the shadow of any image is merged with the foreground object then the detection process becomes more complex.

Research of orientation characteristics of visual intersection illusion

During visual perception of an inclined line, partially passing behind an opaque object, an error (Poggendorff illusion) arises assosiated with an inadequate extrapolation of the line extension after its passing behind the object. The quantitative relations of the illusion values of displacement from the geometric and orientational parameters of the Poggendorf configuration are determined.

A Vision-Based Path Planning and Object Tracking Framework for 6-DOF Robotic Manipulator

Industrial robots are widely used for repetitive, humanly unmanageable, and hazardous tasks. Hence, an improvement in the production efficiency of industrial robot manipulators is of prime concern. This can be achieved through machine vision and path planning techniques with a focus on localization and shortest path calculation. In particular, this is important for manufacturing and bottle filling industries which extensively use robotic manipulators to place/displace bottles during production and post refill placements. This is even more challenging when soft, fragile, or opaque objects have to be detected, since it is significantly difficult for robot vision to focus on their indistinguishable features. To this end, we present an ensemble robot framework with a stereo vision system for tracking colored objects which are sensed using blob analysis. An ensemble robotic framework with neural networks is proposed for predicting and thereby overcoming the inbuilt geometric error present in stereo vision systems. Moreover, we have simplified 2-D correspondence problem to 1-D by using a non-rectified stereo camera model and object tracking by applying the triangulation technique in 3D stereo vision coordinate system (SVCS). Subsequently, the SVCS is transformed into robot stereo vision coordinate system for tracking the object centroid by using an RGB marker placed on the object. Finally, in the learning model we have combined color region tracking with machine learning to achieve high accuracy. The outcomes are in accordance with the designed model and successfully achieve path prediction with up to 91.8% accuracy.

Performance Trade-Offs of an Optical Wireless Communication Network Deployed in an Aircraft Cockpit

In this article, we explore the performance of optical wireless technology for ensuring audio communications inside an aircraft cockpit. One advantage is that, unlike radio frequencies, opaque objects block optical signals and, therefore, signals cannot pass through walls. This can reduce security risks against eavesdropping and hacking of the physical layer, which is one of the main concerns in the aviation environment. However, optical wireless technology faces some issues, including range limitation and sensitivity to blockages. To study the achievable performances, we propose a modeling of the channels for the uplink and the downlink between the headsets of the four pilots of an Airbus A350 and the access point at the cockpit ceiling. A ray-tracing approach associated with a Monte-Carlo method takes into account the 3D geometric model of the cockpit, the presence of the pilots and their movements. We show that using spatial diversity for headset transceivers can improve performance. Using IEEE 802.11 medium access control mechanism to ensure multi-user communication, the approach highlights the trade-offs between power and delay for a successful communication, linked to the maximum achievable data rate for a given performance level.