Structured Light

The tools and standards of best practice adopted by natural science (NS) and cultural heritage (CH) professionals will determine the digital future of NS and CH digital imaging work. This tutorial discusses emerging digital technologies and explores issues influencing widespread adoption of digital practices for NS and CH. The tutorial explores a possible digital future for NS and CH through key concepts; adoption of digital surrogates, empirical (scientific) provenance, perpetual digital conservation, and 'born archival' semantic knowledge management. The tutorial discusses multiple image based technologies along with current research including; Reflectance Transformation Imaging (RTI), Photometric Stereo, and new research in the next generation of multi-view RTI. This research involves extending stereo correspondence methods. These technologies permit generation of digital surrogates that can serve as trusted representations of 'real world' content. The tutorial explores how empirical provenance contributes to the reliability of digital surrogates, and how perpetual digital conservation can ensure that digital surrogates will be archived and available for future generations. The tutorial investigates the role of semantically based knowledge management strategies and their use in simplifying ease of use by natural science and CH professionals as well as long term preservation activities. The tutorial also investigates these emerging technologies' potential to democratize digital technology, making digital tools and methods easy to adopt and make NS and CH materials widely available to diverse audiences. The tutorial concludes with handson demonstrations of image-based capture and processing methods and a practical problem solving Q&A with the audience.

Structured-light systems are simple and effective tools to acquire 3D models. Built with off-the-shelf components, a data projector and a camera, they are easy to deploy and compare in precision with expensive laser scanners. But such a high precision is only possible if camera and projector are both accurately calibrated. Robust calibration methods are well established for cameras but, while cameras and projectors can both be described with the same mathematical model, it is not clear how to adapt these methods to projectors. In consequence, many of the proposed projector calibration techniques make use of a simplified model, neglecting lens distortion, resulting in loss of precision. In this paper, we present a novel method to estimate the image coordinates of 3D points in the projector image plane. The method relies on an uncalibrated camera and makes use of local homographies to reach sub-pixel precision. As a result, any camera model can be used to describe the projector, including the extended pinhole model with radial and tangential distortion coefficients, or even those with more complex lens distortion models.

We present a new endoscopic 3D scanning system based on Single Shot Structured Light. The proposed design makes it possible to build an extremely small scanner. The sensor head contains a catadioptric camera and a pattern projection unit. The paper describes the working principle and calibration procedure of the sensor. The prototype sensor head has a diameter of only 3.6 mm and a length of 14 mm. It is mounted on a flexible shaft. The scanner is designed for tubular cavities and has a cylindrical working volume of about 30 mm length and 30 mm diameter. It acquires 3D video at 30 frames per second and typically generates approximately 5000 3D points per frame. By design, the resolution varies over the working volume, but is generally better than 200 lm. A prototype scanner has been built and is evaluated in experiments with phantoms and biological samples. The recorded average error on a known test object was 92 lm.

Automatic 3D acquisition devices (often called 3D scanners) allow to build highly accurate models of real 3D objects in a cost-and time-effective manner. We have experimented this technology in a particular application context: the acquisition of Cultural Heritage artefacts. Specific needs of this domain are: medium-high accuracy, easy of use, affordable cost of the scanning device, self-registered acquisition of shape and color data, and finally operational safety for both the operator and the scanned artefacts. According to these requirements, we designed a low-cost 3D scanner based on structured light which adopts a new, versatile colored stripe pattern approach. We present the scanner architecture, the software technologies adopted, and the first results of its use in a project regarding the 3D acquisition of an archeological statue.

In computer vision, two major active range imaging methods have been frequently employed for rapid and efficient shape recovery: (a) conventional active stereo vision and (b) conventional structured-light vision. This paper presents a comparative analysis and an integration of the two active approaches, namely, a structured-light stereo approach for the acquisition of dynamic shape. We first investigate the strengths and weaknesses of the two approaches in terms of accuracy, computational cost, field of view, depth of field, and color sensitivity. Based on this analysis, we propose a novel integrated method, the structured-light stereo, to recover dynamic shapes from a wider view with less occlusion by taking most of the benefits of the two approaches. The main idea is as follows. We first build a system composed of two cameras and a single projector (just a basic setup for conventional active stereo), and the projector projects a single “one-shot” color-stripe pattern. The next step is to estimate reliable correspondences between each camera and the projector via an accurate and efficient pattern decoding technique, and some remaining unresolved regions are explored by a stereo matching technique, which is less sensitive to object surface colors and defocus due to the projector's short depth of field, to estimate additional correspondences. We demonstrate the efficacy of the integrated method through experimental results.

The on-going decipherment and study of Classic Maya writing and iconography relies on timely publication of accurate line drawings and photographs of monuments and artifacts. Far from mere mechanical reproductions, such photographs and drawings reflect one's expert judgment and aesthetic preferences. Given that most monuments have suffered from intentional damage or erosion, line drawings constitute a key step between the epigrapher's initial interpretation of an inscription and/or imagery and its wider dissemination among scholars and wider academic and non -academic audiences. The digital photogrammetry offers a new level of precision and verifiability in the production of epigraphic illustrations, as it enables sharing of primary 3D data alongside its interpretation as renderings and drawings, potentially signaling a new era in the study of Classic Maya heritage. This presentation explores the emerging practice of digital epigraphy and it contribution to advancing our understanding of ancient monuments through a series of examples and case studies.

Linear perspective projection has served as the dominant imaging model in computer vision. Recent developments in image sensing make the perspective model highly restrictive. This paper presents a general imaging model that can be used to represent an arbitrary imaging system. It is observed that all imaging systems perform a mapping from incoming scene rays to photo-sensitive elements on the image detector. This mapping can be conveniently described using a set of virtual sensing elements called raxels. Raxels include geometric, radiometric and optical properties. We present a novel calibration method that uses structured light patterns to extract the raxel parameters of an arbitrary imaging system. Experimental results for perspective as well as non-perspective imaging systems are included.

Coded structured light is considered one of the most reliable techniques for recovering the surface of objects. This technique is based on projecting a light pattern and viewing the illuminated scene from one or more points of view. Since the pattern is coded, correspondences between image points and points of the projected pattern can be easily found. The decoded points can be triangulated and 3D information is obtained. We present an overview of the existing techniques, as well as a new and deÿnitive classiÿcation of patterns for structured light sensors. We have implemented a set of representative techniques in this ÿeld and present some comparative results. The advantages and constraints of the di erent patterns are also discussed.

Appropriate comparative animal skeletons are not always available to faunal analysts for use in identifying archaeofaunal remains. This is especially pertinent when working in locations where no comparative collections are available locally, and the archaeological assemblage cannot be transported to another facility. In order to fill this gap, we are building a virtual comparative faunal collection using a structured light scanner to scan modern skeletal material in 3D. The resulting high resolution 3D color models are a valuable resource for identifying fossil specimens. Scan data can be converted into a variety of formats for viewing and can be transported on a portable digital device for use at field or laboratory localities. In addition, scans can be printed three dimensionally to produce a replica of the scanned skeletal part. A particular advantage of this digital technology is that we can eventually create a complete 3D representation of a taxon's skeleton from scans of several components of what are incomplete skeletons of one animal taxon in a museum collection. The results of our project thus far are available to other researchers and educators by means of the internet. A variety of interested parties could benefit from such a collection, including zooarchaeologists, paleontologists, biologists, teachers and museum curators.

In recent years, various methodologies of shape reconstruction have been proposed with the aim at creating Computer-Aided Design models by digitising physical objects using optical sensors. Generally, the acquisition of 3D geometrical data includes crucial tasks, such as planning scanning strategies and aligning different point clouds by multiple view approaches, which differ for user’s interaction and hardware cost. This paper describes a methodology to automatically measure three-dimensional coordinates of fiducial markers to be used as references to align point clouds obtained by an active stereo vision system based on structured light projection. Intensity-based algorithms and stereo vision principles are combined to detect passive fiducial markers localised in a scene. 3D markers are uniquely recognised on the basis of geometrical similarities. The correlation between fiducial markers and point clouds allows the digital creation of complete object surfaces. The technology has been validated by experimental tests based on nominal benchmarks and reconstructions of target objects with complex shapes.

Fringe pattern analysis in coded structured light constitutes an active field of research. Techniques based on first projecting a sinusoidal pattern and then recovering the phase deviation permit the computation of the phase map and its corresponding depth map, leading to a dense acquisition of the measuring object. Among these techniques, the ones based on time-frequency analysis permit to extract the depth map from a single image, thus having potential applications measuring moving objects. The main techniques are Fourier Transform (FT), Windowed Fourier Transform (WFT) and Wavelet Transform (WT). This paper first analyzes the pros and cons of these three techniques, then a new algorithm for the automatic selection of the window size in WFT is proposed. This algorithm is compared to the traditional WT using adapted mother wavelet signals both with simulated and real objects, showing the performance results for quantitative and qualitative evaluations of the new method.

The following contribution focuses on the low-cost Shining 3D EinScan-Pro scanner, above all the analysis of its precision and accuracy. The need to prove the functioning of this instrumentation in practical cases (the sculptures by Eduardo Chillida preserved in the Chillida-Leku Museum and along with some artefacts collected in the Archaeological Museum of Sarno), has led to the comparison and validation of the instrument through a methodology necessarily diversified from the guideline VDI/VDE 2634, part 2 and part 3, characteristics to the test the optical 3D measuring systems with planar measurement, which works according to the triangulation principle. In particular, two types of comparisons were made: geometric-formal and metric-dimensional. The first type of analysis was carried out analysing the geometric parameters of the models, suitable for validating the information: dimensional (difference between some main measurements); superficial (total mesh extension) and of the form (that is, the discrepancies returned through a DEM analysis). The second type of analysis, instead, of the metric type, was carried out. The complete results of the various analyses will be presented and critically discussed within this contribution in order to prove the stability and the metric quality of this hand-held EinScan-Pro, following the comparison with medium-high end systems now well established in the field of cultural heritage survey.

We present a survey of the most significant techniques, used in the last few years, concerning the coded structured light methods employed to get 3D information. In fact, depth perception is one of the most important subjects in computer vision. Stereovision is an attractive and widely used method, but, it is rather limited to make 3D surface maps, due to the correspondence problem. The correspondence problem can be improved using a method based on structured light concept, projecting a given pattern on the measuring surfaces. However, some relations between the projected pattern and the reflected one must be solved. This relationship can be directly found codifying the projected light, so that, each imaged region of the projected pattern carries the needed information to solve the correspondence problem.

Shape reconstruction using coded structured light is considered one of the most reliable techniques to recover object surfaces. Having a calibrated projector-camera pair, a light pattern is projected onto the scene and imaged by the camera. Correspondences between projected and recovered patterns are found and used to extract 3D surface information. This paper presents an up-to-date review and a new classification of the existing techniques. Some of these techniques have been implemented and compared, obtaining both qualitative and quantitative results. The advantages and drawbacks of the different patterns and their potentials are discussed.

Three different methods for measuring dynamic dough density during proofing were investigated. The three methods included: monitoring the change in apparent mass of a dough piece suspended in silicone oil at 35°C; monitoring the change in dough volume during actual proofing conditions with a novel imaging technique using structured lighting; and finally monitoring the dough volume changes in a rheofermentometer at 35°C. All the methods resulted in similar dough density profiles. However, dough density appeared to level off sooner when the oil displacement method was used. This was not the case with the other two methods where density continued to decrease up to the end of proofing. Dough density at the end of fermentation process was related to the loaf volume after baking. The novel structured lighting method had the advantage of being low cost and measuring dough density in actual proofing conditions as used in breadmaking.

The ongoing project of 3D documentation of Copan sculptures by the Corpus of Maya Hieroglyphic Inscriptions of the Peabody Museum of Archaeology and Ethnology created additional opportunities to explore the application of the technology to a wider set of artifacts and materials. One of these sideline projects centered on chert artifacts known as " eccentrics " or often referred to as " eccentric flints. " The principal goal of 3D scanning of the nine eccentric cherts and three bifaces from the Rosalila cache was to facilitate measurement and study of these elaborate stone artifacts without endangering fragile textile fragments adhering to their surface.

In this paper, the procedure developed to calibrate a whole-field optical profilometer and the evaluation of the measurement performance of the system are presented. The sensor is based on the projection of structured light and on active triangulation. The dependence of the measurements on the geometric parameters of the system is shown, as well as the criterion to calibrate the system. From the extensive set of experiments carried out to evaluate the measurement performance, good linearity has been observed, and an overall mean value of the measurement error equal to 40 m, with a variability of about 35 m has been estimated.

This work is motivated by two important trends in consumer computing: (i) the growing pervasiveness of mobile computing devices, and (ii) the users' desire for increasingly complex but readily acquired and manipulated information content. Specifically, we develop and describe a system for 3D model creation of an object, using only a standard mobile device such as a smart phone. Our approach applies the structured light projection methodology and exploits multiple image input such as frames from a video sequence. In comparison with previous work, a significant further challenge addressed here is that of lower quality input data and limited hardware (processing power and memory, camera and projector quality). Novelties include: (i) a comparison of projection pattern detection approaches in the context of a mobile environment - a robust method combining colour detection and a phase congruency descriptor is proposed, (ii) a model for single view reconstruction which exploits epipolar, coplanarity and topological constraints, (iii) the use of mobile device sensor data in the iterative closest point algorithm used to register multiple partial 3D reconstructions, and (iv) two heuristics for determining the order in which buffered single view based reconstructions are merged. Our experiments demonstrate that visually appealing results are obtained in a speedy manner which does not require specialist knowledge or expertise from the user.

In this paper, a fast and accurate rail wear measurement method based on simple equipments is presented. The inner rail profile is measured by a line structured light vision sensor. Using the centers of the big and small circle from the rail waist profile as control points, the measured rail profile is registered to the reference profile. The rail wear, including the vertical and horizontal rail wear, is computed by comparing the registered measured profile with the reference profile. The method has three key contributions: (1) the rail waist light stripe center points in the images are located fast and accurately by first tracking the region containing the rail waist light stripe using the Kalman filter and then computing the sub-pixel precision image coordinates by Hessian matrix at pixels. The rail waist profile is segmented automatically into arcs of big and small circles by thresholding the normal angle curve of the measured rail waist profile. The centers of the two circles are used as control points for registering the measured rail profile to the reference profile. (3) The fast location of rail wear points in the images is realized by projecting the rail wear constraint points to the image, which simplifies the problem of computing rail wear from 2d image processing to 1d searching along the line segment connecting two rail wear constraint points. Experiments show that the proposed method can achieve 500 fps measurement frequency. At a train speed of 350 km/h, the interval between two consecutive measurements is about 190 mm. The system is tested on a real running train, and the measurement results are compared with those rail wear measured manually by special gage. The RMS errors of vertical and horizontal rail wears are 0.34 and 0.30 mm, respectively.

Every year, maritime archaeologists around the globe are faced with the daunting task of recording hundreds, if not thousands, of individual ship timbers. The in-depth recording of ship timbers is a process which is both challenging and laborious, but it is an indispensable step in order to fully understand the construction of the ship the timbers formed a part of, and as archaeologists it is our duty to document all the information these complex artefacts hold to the best of our abilities. In this article, the authors first provide an overview of the methods currently in use for ship timber recording, namely 2D scaled drawing, 2D tracing, 3D contact digitising and 3D scanning. The respective advantages and limitations of these methods are then discussed in light of the various scientific and practical considerations that go into choosing a recording method for a project. Next, a new approach to ship timber recording, termed the “3D annotated scans method”, is introduced and discussed using a recent case study in northern Germany. At its core the method consists of two phases; a 3D scanning phase in which the timber is scanned in 3D, followed by a 3D annotation phase in which the recorder interprets the timber by tracing diagnostic features such as fasteners and toolmarks directly onto the timber’s digital model. The authors conclude that this new approach represents an improvement over current methods—both in terms of the quality of the scientific outputs and in terms of recording efficiency—and that, besides being implemented for the recording of ship timbers, the same method can also be used for a wide range of other heritage applications.

Reverse engineering and in particular threedimensional digitization have become an essential part of the documentation of archaeological findings. 3D scanning produces a high-precision digital reference document. The factors that influence the quality of the 3D scanned data are the scanned object's surface colour, its glossiness and geometry, and the ambient light during the scanning process. However, the actual equipment and scanning technologies are of primary importance. The current paper presents a qualitative and quantitative comparison between two 3D scanning devices of different technologies; structured light 3D scanning and laser 3D scanning. The benchmark for this comparison is an ancient Roman vase from the city of Thessaloniki, Greece. The object was scanned with every possible setting on each scanner, but only one configuration of settings on each device was selected for the final comparison. The main criterion for the final selection of the two 3D models acquired with the use of the two technologies was the proximity in the number of points and polygons produced for digitally restoring the ancient vase in the best possible way. The results indicate important differences regarding the accuracy of the final digital model. The laser technology produced better accuracy but with a significant cost in scanning time and model data size. On the other hand, the structured light technology achieved the optimal combination of scanning quality and accuracy, along with reduced acquisition time of scan data.

An imaging model provides a mathematical description of correspondence between points in a scene and in an image. The dominant imaging model, perspective projection, has long been used to describe traditional cameras as well as the human eye. We propose an imaging model which is flexible enough to represent an arbitrary imaging system. For example using this model we can describe systems using fisheye lenses or compound insect eyes, which violate the assumptions of perspective projection. By relaxing the requirements of perspective projection, we give imaging system designers greater freedom to explore systems which meet other requirements such as compact size and wide field of view. We formulate our model by noting that all imaging systems perform a mapping from incoming scene rays to photosensitive elements on the image detector. This mapping can be conveniently described using a set of virtual sensing elements called raxels. Raxels include geometric, radiometric and optical properties. We present a novel ray based calibration method that uses structured light patterns to extract the raxel parameters of an arbitrary imaging system. Experimental results for perspective as well as non-perspective imaging systems are included.

We report the first experimental realization of all-optical trapping and manipulation of plasmonic nanowires in three dimensions. The optical beam used for trapping is the Fourier transform of a linearly polarized Bessel beam (termed FT-Bessel). The extended depth of focus of this beam enables the use of a retroreflection geometry to cancel radiation pressure in the beam propagation direction, making it possible to trap highly scattering and absorbing silver nanowires. Individual silver nanowires with lengths of several micrometers can be positioned by the trapping beam with a precision better than 100 nm and are oriented by the polarization of the trapping light with a precision of approximately 1°. Multiple nanowires can be trapped simultaneously in spatially separated maxima of the trapping field. Since trapping in the interferometric FT-Bessel potential is robust in bulk solution and near surfaces, it will enable the controlled assembly of metal nanowires into plasmonic nanostructures.

This work presents a new technique for automatically generating the 3D scanning surface for acoustic imaging using microphone arrays. Acoustic images, or maps, of sound coming from spatially distributed sources, may be generated from microphone array data using algorithms such as beamforming. Traditional 2D acoustic maps can contain errors in the near-field if the object being imaged has a 3D shape. It has been shown that using the 3D surface geometry of an object as a scanning surface for beamforming can provide more accurate results. The methods used previously to generate this 3D scanning surface have either required existing CAD (Computer-Aided Design) models of the object being acoustically imaged or have required separate equipment which is generally bulky and expensive. The new method uses one or more cameras in the array, a data projector, and structured light code to automatically generate the 3D scanning surface. This has the advantage that it is inexpensive, can be incorporated as an add-onto existing microphone arrays, has short scan time, and is capable of being extended to imaging dynamic scenes. This technique is tested using beamforming and CLEAN-SC (CLEAN based on spatial Source Coherence) algorithms for a spherical array and an Underbrink multi-arm spiral array. For sound sources located about 1.2 m from the array, the mean position errors obtained are 6 mm. This is a quarter of the diameter of the mini-speakers being used as a sound sources.

We present a new method for improving the measurement of three-dimensional ͑3-D͒ shapes by using color information of the measured scene as an additional parameter. The widest used algorithms for 3-D surface measurement by use of structured fringe patterns are phase stepping and Fourier fringe analysis. There are a number of problems and limitations inherent in these algorithms that include: that the phase maps produced are wrapped modulo 2, that in some cases the acquired fringe pattern does not fill the field of view, that there may be spatially isolated areas, and that there is often invalid and͞or noisy data. The new method presented to our knowledge for the first time here uses multiple colored fringe patterns, which are projected at different angles onto the measured scene. These patterns are analyzed with a specially adapted multicolor version of the standard Fourier fringe analysis method. In this way a number of the standard difficulties outlined above are addressed.

Motivated by the requirements of the present archaeology, we have been developing an automated archivation system for archaeological classification and reconstruction of ceramics. Our system works with the profile of an archaeological fragment, which is the cross-section of the fragment in the direction of the rotational axis of symmetry. Ceramic fragments are recorded automatically by a 3D-measurement system based on structured light. The input data for the estimation of the profile is a set of points produced by the acquisition system. The profile is used to reconstruct the original pot. Our approach consists of several steps, starting by calculating the proper orientation, which describes the exact positioning of the fragment on the original vessel. Next the profile line is computed and several measurements, like the diameter and height of the vessel. After evaluating the profile line a virtual pot is reconstructed. The performance of the proposed algorithm was tested on real data and the results are presented in this paper.

Three-dimensional (3D) image acquisition systems are rapidly becoming more affordable, especially systems based on commodity electronic cameras. At the same time, personal computers with graphics hardware capable of displaying complex 3D models are also becoming inexpensive enough to be available to a large population. As a result, there is potentially an opportunity to consider new virtual reality applications as diverse as cultural heritage and retail sales that will allow people to view realistic 3D objects on home computers.Although there are many physical techniques for acquiring 3D data—including laser scanners, structured light and time-of-flight—there is a basic pipeline of operations for taking the acquired data and producing a usable numerical model. We look at the fundamental problems of range image registration, line-of-sight errors, mesh integration, surface detail and color, and texture mapping. In the area of registration we consider both the problems of finding an initial global alignment using manual and automatic means, and refining this alignment with variations of the Iterative Closest Point methods. To account for scanner line-of-sight errors we compare several averaging approaches. In the area of mesh integration, that is finding a single mesh joining the data from all scans, we compare various methods for computing interpolating and approximating surfaces. We then look at various ways in which surface properties such as color (more properly, spectral reflectance) can be extracted from acquired imagery. Finally, we examine techniques for producing a final model representation that can be efficiently rendered using graphics hardware.

Understanding the effect of canopy structure on the understory light environment is useful in the design of silvicultural strategies that facilitate sustainable tree recruitment. To address this need, a study was designed to quantify the relationship between forest structure and light along a gradient of 50-100% canopy cover. The gradient was created by applying 1 of 4 midstory removal treatments to each of fifty 0.05 ha plots located within a mixed-hardwood riparian forest corridor. The light environment was directly quantified with a linear ceptometer and regression analysis was used to examine the relationship between photosynthetically active radiation (PAR) and various metrics of vertical and horizontal structure. Vertical sighting tube estimates of canopy cover (R 2 = 0.73), light estimates derived from hemispherical photography (R 2 = 0.70), and spherical densiometer estimates of canopy closure (R 2 = 0.68) were the best single predictors of understory light transmittance. Including top height and tree density improved the fit of canopy cover based models (R 2 = 0.80). Canopy closure estimates derived from hemispherical photography generally showed a weaker relationship with PAR than other measures of stand structure. Further, the strength of this relationship depended upon photo analysis angle. In general, the vertical component of stand structure seems to influence light transmittance through the forest canopy. This vertical complexity must be addressed when evaluating structure-light relations. #

For structured-light range imaging, colour stripes can be used for increasing the number of distinguishable light patterns compared to binary black-and-white stripes. Therefore, an appropriate use of colour patterns can reduce the number of required light projections for imaging an object scene, and range imaging can be achievable in a single video frame or in “one-shot”. On the other hand, the reliability and range resolution attainable from colour stripes are generally lower than those from temporally encoded binary black-and-white patterns since colour contrast is affected by object colour reflectance and ambient light. This paper presents new methods for selecting stripe colours and designing multiple-stripe patterns for “one-shot” and “two-shot” imaging. We show that maximizing colour contrast between the stripes in one-shot imaging reduces the ambiguities resulting from coloured object surfaces and limitations in sensor/projector resolution. Moreover, a cross-stripe gradient method is presented to improve estimation of illumination patterns in one-shot imaging. Two-shot imaging adds an extra video frame and maximizes the colour contrast between the first and second video frames to diminish the ambiguities even further. Experimental results and discussion demonstrate the effectiveness and robustness of the presented one-shot and two-shot colour-stripe imaging schemes.

This article introduces the annotated scans method as a new approach to ship timber recording. The proposed method consists of several phases: timbers are first scanned in 3D, these scans are then annotated in Rhino, and finally the timber catalogue is generated using a semi-automated workflow. We compare this approach to the current best practice method for timber recording, namely contact digitising. Based on our experience recording the timbers of the Wismar 'Big Ship', we conclude that the proposed method matches, and in some regards surpasses the current best practice method, most notably in terms of cost and time efficiency.

3D acquisition techniques to measure dynamic scenes and deformable objects with little texture are extensively researched for applications like the motion capturing of human facial expression. To allow such measurement, several techniques using structured light have been proposed. These techniques can be largely categorized into two types. The first involves techniques to temporally encode positional information of a projector's pixels using multiple projected patterns, and the second involves techniques to spatially encode positional information into areas or color spaces. Although the former allows dense reconstruction with a sufficient number of patterns, it has difficulty in scanning objects in rapid motion. The latter technique uses only a single pattern, so this problem can be resolved, however, it often uses complex patterns or color intensities, which are weak to noise, shape distortions, or textures. Thus, it remains an open problem to achieve dense and stable 3D acquisition in real cases. In this paper, we propose a technique to achieve dense shape reconstruction that requires only a single-frame image of a grid pattern. The proposed technique also has the advantage of being robust in terms of image processing.

This paper presents a new personal authentication system that simultaneously exploits 2D and 3D palmprint features. The objective of our work is to improve accuracy and robustness of existing palmprint authentication systems using 3D palmprint features.

Full field optical techniques can be reliably used for 3D measurements of complex shapes by multiview processes, which require the computation of transformation parameters relating different views into a common reference system. Although, several multi-view approaches have been proposed, the alignment process is still the crucial step of a shape reconstruction.

This paper presents the experimental results of 3D underwater reconstructions based on a combination of structured light and stereo-photogrammetry. Structured lighting patterns are projected by a video projector and acquired by a stereo vision system for a whole-field 3D reconstruction. We describe the experimental setup used for the underwater tests in water tank, with different turbidity conditions. The quality of 3D reconstruction comes up to be acceptable even with high turbidity values, despite the heavy presence of scattering and absorption effects. In this work we have tested and analysed the results of a well-known optical technique -frequently used in air for industrial and Cultural Heritage applications -in underwater environment. We also tested the performance of this acquisition method for underwater applications with small field of view.

Active range sensing using structured-light is the most accurate and reliable method for obtaining 3D information. However, most of the work has been limited to range sensing of static objects, and range sensing of dynamic (moving or deforming) objects has been investigated recently only by a few researchers. Sinusoidal structured-light is one of the well-known optical methods for 3D measurement. In this paper, we present a novel method for rapid high-resolution range imaging using color sinusoidal pattern. We consider the real-world problem of nonlinearity and color-band crosstalk in the color light projector and color camera, and present methods for accurate recovery of color-phase. For high-resolution ranging, we use high-frequency patterns and describe new unwrapping algorithms for reliable range recovery. The experimental results demonstrate the effectiveness of our methods.

In this paper we present a theoretical method, together with its experimental confirmation, to obtain structures of light by connecting diffraction-resistant cylindrical beams of finite lengths and different radii. The resulting ``Lego-beams'' can assume, on demand, various
interesting spatial configurations. We experimentally generate
some of them by using a computational holographic technique and a
Spatial Light Modulator. Our results can find applications in all
fields where structured light beams are needed, such as optical
tweezers, optical guiding of atoms, light orbital angular momentum
control and others. [OCIS codes: (999.9999) Non-diffracting waves; (260.1960) Diffraction theory; (070.7545) Wave propagation; (050.1120)
Apertures; (050.1755) Computational electromagnetic methods].

CITATIONS 0 READS 74 12 authors, including: Some of the authors of this publication are also working on these related projects: Epithermal suite of metals in modern seafloor massive sulfides at the unique shallow-submarine arcvolcano, Kolumbo (Santorini), Greece View project Ancient coastlines of the Black Sea and conditions for human presence/ДО 02-337 "Древни брегови линии на Черно море и условия за човешко присъствие" View project

This paper deals with 3D shape reconstruction using a structured light system (SLS) which projects a matrix of laser rays onto the scene to be analyzed. The intrinsic problem of such a system is the correspondence problem solving, which in this particular case amounts to matching up the imaged spots and the originating laser rays. In this paper, we propose a method for automatically obtaining configurations of the system (COS) (i.e. the relative positions of the camera, laser projector, and measuring scene) that permit to achieve a direct and unambiguous correspondence. After, we propose a splitting cell algorithm, which efficiently performs a real-time correspondence procedure. Experimental results obtained from both simulated and real data demonstrate that our method provides our SLS with possibilities for real-time applications.

Poor visibility conditions due to murky water, bad weather, dust and smoke severely impede the performance of vision systems. Passive methods have been used to restore scene contrast under moderate visibility by digital postprocessing. However, these methods are ineffective when the quality of acquired images is poor to begin with. In this work, we design active lighting and sensing systems for controlling light transport before image formation, and hence obtain higher quality data. First, we present a technique of polarized light striping based on combining polarization imaging and structured light striping. We show that this technique out-performs different existing illumination and sensing methodologies. Second, we present a numerical approach for computing the optimal relative sensor-source position, which results in the best quality image. Our analysis accounts for the limits imposed by sensor noise.

Since 1984, Graphical User Interfaces have typically relied on visual icons that mimic physical objects like the folder, button, and trash can, or canonical geometric elements like menus, and spreadsheet cells. GUIs leverage our intuition about the physical environment. But the world we inhabit can be regarded as made of stuff as well as things. In order to make interfaces from this point of view requires a way to simulate the physics of stuff in realtime response to continuous gesture, driven by behavior logic that can be understood by the user and the designer. We argue for leveraging the corporeal intuition that we learn from birth about heat flow, water, smoke, to develop interfaces at the density of matter that leverage in turn the state of the art in computational physics.

A novel method for noncontact visual measurement of the profile of surfaces is described. Sinusoidal color fringe patterns are projected onto the surface to be measured, which is then viewed with a color camera. From examination of the red, green, and blue components of a single color image the depth at each point on the surface is determined from the calculation of relative phase shifts.

Nowadays, the high speed (e.g., kilo-Hertz) refreshing rate of the digital micro-mirror device (DMD) has
enabled superfast 3D shape measurement using the binary defocusing technique. This research finds that
when the system reaches its extreme binary pattern refreshing rate, the transient response of the DMD
induces a coupling effect (i.e., two neighboring patterns blend together) that may cause substantial
measurement error. Since this transient response repeats itself, this systematic measurement error is
substantially reduced to a negligible level when the timing between the projector and the camera is
properly adjusted. Experimental results are presented to demonstrate the observed phenomena, and the
success of utilizing the proposed method to overcome the problems associated with the transient
response of the DMD.

Interaction with 3D information is one of the fundamental and most familiar tasks in virtually all areas of engineering and science. Several recent technological advances pave the way for developing hand gesture recognition capabilities available to all, which will lead to more intuitive and e cient 3D user interfaces (3DUI). These developments can unlock new levels of expression and productivity in all activities concerned with the creation and manipulation of virtual 3D shapes and, specifically, in engineering design.

This article presents a concise short overview of the development of the steel industry in Brazil, with the emphasis on civil construction. The relatively rapid increase in the application of steel structures for both low and tall buildings and the modern bridges in Brazil are the results of an extensive effort of the steel producers and the improvement of steel courses and research programmes in several universities and institutions during the last two decades. The steel industry in collaboration with the universities, which have provided the results of their recent studies, contributed to the improved steel technologies and composite construction. Data, supplied by the Brazilian Institute of Metallurgy, IBS, is presented on the actual steel production and fabrication with regard to application in civil engineering. Case studies of steel structures, such as multi-storey buildings, space structures, light gauge steel construction and bridges, are presented and commented on. Further, steel structures subjected to corrosion or to fire, as well as steel and composite semi-rigid joints, are mentioned and finally the Brazilian experience with steel architecture is introduced.

In this study, structural light-weight concretes produced by Pumice (LWC) and concretes with normal-weight aggregate (NWC) were investigated. Compressive strength and weight loss of the concretes were determined after being exposed to high temperatures (20, 100, 400, 800, 1000 °C). To achieve these objectives, 12 different types of concrete mixtures were produced. In producing the mixtures, silica fume (SF) was used to replace the Portland cement in the ratios of 0%, 5% and 10% by weight. Half of the mixtures were obtained by adding superplasticizers (SP) to the above mixtures in the ratio of 2% by weight. In conclusion; unit weight of LWC was 23% lower than that of NWC. The LWC containing 2% SP could retain 38% of the initial compressive strength. Rate of deterioration was higher in NWC when compared to LWC. The loss of compressive strengths increased depending on the ratio of using SF at about 800 °C and over.

Although phase shifts (PS) are frequently used to acquire colored surfaces of static objects, especially when acquisition time is not critical, the periodic nature of relative (wrapped) PS maps makes it necessary to deal with the issue of phase unwrapping. Consequently, multiple phase shifts (MPS) have been widely used as an alternative, but this usually involves a large number of

This paper presents a hybrid contact-optical coordinate measuring system which was designed to measure and analyze the geometry of objects. It combines the accuracy of contact measurement regarding the identification of measurement points and the speed of full-field structured light optical scanning methods. The measurement process starts from fast optical acquisition by structured light system(s), positioned around the working space, then numerical analysis is performed to calculate a set of surface points that should be finally re-measured by the CMM. Both set-ups work in a common coordinate system created according to existing metrological strategies. Final metrological analysis is performed using classic, certified metrological software. In this paper we also describe the maximum permissible error of length measurement of the hybrid system.

We present a 3D vision system based on the projection of a single fringe pattern of incoherent light and on robust phase coding. A novel projection scheme is exploited: two sinusoidal gratings at different frequencies are combined into a single pattern, and phase demodulated in the natural domain of the signal. The method yields the determination of two phase maps, whose sensitivity to height variations is proportional to the frequencies of the two grating components. Robust phase unwrapping is implemented, where the phase ambiguity of the fine grating component is naturally compensated for by the phase values evaluated by using the coarse one. As a result, both a high measurement resolution and an extended height range are obtained. The method requires the projection of a static pattern. Hence, even a low-cost slide projector can be used as the projection device. Moreover, the system turns out to be suitable for dynamic and real-time measurement applications. In addition, it may be fruitfully used as the acquisition sensor in full-optical reverse engineering applications. In this paper, the measurement principle and the design issues of the instrument are presented. The measurement performances are discussed, in relation to both the input-output characteristic of the instrument and the acquisition of free-form shapes.