3,031 research outputs found
Demodulation of Spatial Carrier Images: Performance Analysis of Several Algorithms Using a Single Image
http://link.springer.com/article/10.1007%2Fs11340-013-9741-6#Optical full-field techniques have a great importance in modern experimental mechanics. Even if they are reasonably spread among the university laboratories, their diffusion in industrial companies remains very narrow for several reasons, especially a lack of metrological performance assessment. A full-field measurement can be characterized by its resolution, bias, measuring range, and by a specific quantity, the spatial resolution. The present paper proposes an original procedure to estimate in one single step the resolution, bias and spatial resolution for a given operator (decoding algorithms such as image correlation, low-pass filters, derivation tools ...). This procedure is based on the construction of a particular multi-frequential field, and a Bode diagram representation of the results. This analysis is applied to various phase demodulating algorithms suited to estimate in-plane displacements.GDR CNRS 2519 “Mesures de Champs et Identification en Mécanique des Solide
Event-based Vision: A Survey
Event cameras are bio-inspired sensors that differ from conventional frame
cameras: Instead of capturing images at a fixed rate, they asynchronously
measure per-pixel brightness changes, and output a stream of events that encode
the time, location and sign of the brightness changes. Event cameras offer
attractive properties compared to traditional cameras: high temporal resolution
(in the order of microseconds), very high dynamic range (140 dB vs. 60 dB), low
power consumption, and high pixel bandwidth (on the order of kHz) resulting in
reduced motion blur. Hence, event cameras have a large potential for robotics
and computer vision in challenging scenarios for traditional cameras, such as
low-latency, high speed, and high dynamic range. However, novel methods are
required to process the unconventional output of these sensors in order to
unlock their potential. This paper provides a comprehensive overview of the
emerging field of event-based vision, with a focus on the applications and the
algorithms developed to unlock the outstanding properties of event cameras. We
present event cameras from their working principle, the actual sensors that are
available and the tasks that they have been used for, from low-level vision
(feature detection and tracking, optic flow, etc.) to high-level vision
(reconstruction, segmentation, recognition). We also discuss the techniques
developed to process events, including learning-based techniques, as well as
specialized processors for these novel sensors, such as spiking neural
networks. Additionally, we highlight the challenges that remain to be tackled
and the opportunities that lie ahead in the search for a more efficient,
bio-inspired way for machines to perceive and interact with the world
Automated tracking of colloidal clusters with sub-pixel accuracy and precision
Quantitative tracking of features from video images is a basic technique
employed in many areas of science. Here, we present a method for the tracking
of features that partially overlap, in order to be able to track so-called
colloidal molecules. Our approach implements two improvements into existing
particle tracking algorithms. Firstly, we use the history of previously
identified feature locations to successfully find their positions in
consecutive frames. Secondly, we present a framework for non-linear
least-squares fitting to summed radial model functions and analyze the accuracy
(bias) and precision (random error) of the method on artificial data. We find
that our tracking algorithm correctly identifies overlapping features with an
accuracy below 0.2% of the feature radius and a precision of 0.1 to 0.01 pixels
for a typical image of a colloidal cluster. Finally, we use our method to
extract the three-dimensional diffusion tensor from the Brownian motion of
colloidal dimers.Comment: 20 pages, 8 figures. Non-revised preprint version, please refer to
http://dx.doi.org/10.1088/1361-648X/29/4/04400
Review: Extending Visible Band Computer Vision Techniques to Infrared Band Images
Infared imaging process bears many similarities to the visible imaging process. If visible band computer vision techniques can be used on infrared images with no or small adjustments it would save us the trouble of redeveloping a whole new set of techniques. However, there are important differences in the practical environmental parameters between visible and infrared bands that invalidates many convenient background assumptions inherent to visible-band computer vision techniques. We review here the underlying reasons why some computer vision techniques can while some cannot be applied directly to infrared images. We also examine a few attempts to extend computer vision to infrared images and discuss their relative merits
Multispectral persistent surveillance
The goal of a successful surveillance system to achieve persistence is to track everything that moves, all of the time, over the entire area of interest. The thrust of this thesis is to identify and improve upon the motion detection and object association aspect of this challenge by adding spectral information to the equation. Traditional motion detection and tracking systems rely primarily on single-band grayscale video, while more current research has focused on sensor fusion, specifically combining visible and IR data sources. A further challenge in covering an entire area of responsibility (AOR) is a limited sensor field of view, which can be overcome by either adding more sensors or multi-tasking a single sensor over multiple areas at a reduced frame rate. As an essential tool for sensor design and mission development, a trade study was conducted to measure the potential advantages of adding spectral bands of information in a single sensor with the intention of reducing sensor frame rates. Thus, traditional motion detection and object association algorithms were modified to evaluate system performance using five spectral bands (visible through thermal IR), while adjusting frame rate as a second variable. The goal of this research was to produce an evaluation of system performance as a function of the number of bands and frame rate. As such, performance surfaces were generated to assess relative performance as a function of the number of bands and frame rate
Observing a Moving Agent
We address the problem of observing a moving agent. In particular, we propose a system for observing a manipulation process, where a robot hand manipulates an object. A discrete event dynamic system (DEDS) from work is developed for the hand/object interaction over time and a stabilizing observer is constructed. Low-level modules are developed for recognizing the events that causes state transitions within the dynamic manipulation system. The work examines closely the possibilities for errors, mistakes and uncertainties in the manipulation system, observer construction process and event identification mechanisms. The system utilizes different tracking techniques in order to observe the task in an active, adaptive and goal-directed manner
Dengue Virus Capsid Protein Dynamics Reveals Spatially Heterogeneous Motion in Live-Infected-Cells
Dengue is the single most important human viral infection transmitted by insects. The function of the viral proteins andtheir interactions with the host cell is under exhaustive investigation with the aim of identifying antiviral strategies. Here,using recombinant full-length dengue virus genomes, carrying a fluorescent mCherry fused to capsid, we studied biophysicalproperties of the viral protein during one infectious cycle in living cells. Dengue virus capsid protein associates to differentcellular compartments but its function in these locations is largely unknown. We evaluated the diffusion of capsid inside the celland determined a higher effective diffusion coefficient in the cytoplasm than in the nucleus. Using advanced fluorescencecorrelation methods, including the recently developed two-dimensional pair correlation analysis, we constructed for the first timehigh resolution maps of capsid mobility in an infected cell. We observed that the motion of capsid in the nucleoplasm-nucleolusinterface was highly organized, indicating an obstacle in this interface. Although nucleoli are membraneless structures, theydisplayed liquid-liquid phase separation. Once inside nucleoli, the protein showed isotropic mobility, indicating free diffusion orimmobilized capsid inside these structures. This is the first study presenting spatial and temporal dynamics of the dengue viruscapsid protein during infection.Fil: Gabriel, Manuela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; ArgentinaFil: Costa Navarro, Guadalupe Soledad. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Instituto de Investigaciones BioquĂmicas de Buenos Aires. FundaciĂłn Instituto Leloir. Instituto de Investigaciones BioquĂmicas de Buenos Aires; ArgentinaFil: de Borba, Luana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Instituto de Investigaciones BioquĂmicas de Buenos Aires. FundaciĂłn Instituto Leloir. Instituto de Investigaciones BioquĂmicas de Buenos Aires; ArgentinaFil: Rossi, AndrĂ©s Hugo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Instituto de Investigaciones BioquĂmicas de Buenos Aires. FundaciĂłn Instituto Leloir. Instituto de Investigaciones BioquĂmicas de Buenos Aires; ArgentinaFil: Gamarnik, Andrea Vanesa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Instituto de Investigaciones BioquĂmicas de Buenos Aires. FundaciĂłn Instituto Leloir. Instituto de Investigaciones BioquĂmicas de Buenos Aires; ArgentinaFil: Estrada, Laura Cecilia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; Argentin
Quantitative imaging of concentrated suspensions under flow
We review recent advances in imaging the flow of concentrated suspensions,
focussing on the use of confocal microscopy to obtain time-resolved information
on the single-particle level in these systems. After motivating the need for
quantitative (confocal) imaging in suspension rheology, we briefly describe the
particles, sample environments, microscopy tools and analysis algorithms needed
to perform this kind of experiments. The second part of the review focusses on
microscopic aspects of the flow of concentrated model hard-sphere-like
suspensions, and the relation to non-linear rheological phenomena such as
yielding, shear localization, wall slip and shear-induced ordering. Both
Brownian and non-Brownian systems will be described. We show how quantitative
imaging can improve our understanding of the connection between microscopic
dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of
methodology. Submitted for special volume 'High Solid Dispersions' ed. M.
Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009);
22 pages, 16 fig
An Architecture for High-throughput and Improved-quality Stereo Vision Processor
This paper presents the VLSI architecture to achieve high-throughput and
improved-quality stereo vision for real applications. The stereo vision processor
generates gray-scale output images with depth information from input images taken by
two CMOS Image Sensors (CIS). The depth estimator using the sum of absolute
differences (SAD) algorithm as stereo matching technique is implemented on hardware
by exploiting pipelining and parallelism. To produce depth maps with improved-quality
at real-time, pre- and post-processing units are adopted, and to enhance the adaptability
of the system to real environments, special function registers (SFRs) are assigned to
vision parameters. The design using 0.18um standard CMOS technology can operate at
120MHz clock, achieving over 140 frames/sec depth maps with 320 by 240 image size
and 64 disparity levels. Experimental results based on images taken in real world and
the Middlebury data set will be presented. Comparison data with existing hardware
systems and hardware specifications of the proposed processor will be given
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